Block Title: Blood & Lymph

Transcription

1 Block Title: Blood & Lymph Module Description: This is an integrated multidisciplinary module. Content is addressed under four main domains; RBCs & anemias, coagulation & coagulopathies, WBCs structure - function & disorders, and related infections & infestations. Learning Activities: Structured lectures, small group knowledge application, linked practical sessions, linked field visits, and multidisciplinary problem oriented team based sessions The sessions sequence and integration are provided in this learning guide. Hemoglobin Structure and Function (Biochemistry) By the end of this lecture, the student should be able to: 1. Understand the globin structure. 2. Understand the heme structure. 3. Justify the location of the heme as a prothetic group inside the globin molecule. 4. Correlate hemoglobin structure with its function. 5. Discuss the O 2 dissociation curve of Hb. Pre-requisite knowledge: Tertiary & quaternary levels of protein organization (Lippincott Chapter 2, pages 22 & 23). Mb and Hb subunits are structurally similar: We have to know that these two proteins are very similar in their basic structure; however, because one of them is a monomer and the other is a heterotetramer, the function differs in a crucial way. Eight -helices in Mb and Hb subunit Seven -helices in Hb subunit The subunits contain heme group 1

2 Heme group: Look at this harmony of O 2 loading and unloading, thanks to the structure of heme and its interaction with the structural changes in the hemoglobin molecule. We will address this in our lecture. Heme is a prothetic group present in a number of oxygen transporting proteins It is a complex organic ring structure called protoporphyrin with an iron atom in its center The iron is in the ferrous (Fe++) oxidation state so it can bind O2 reversibly Heme is positioned in a deep hydrophobic pocket to protect it from being oxidized to (Fe+++) which can not bind O 2 The fifth and sixth coordination positions are perpendicular to the porphyrin ring 2

3 Heme = Fe++ bound to tertapyrrole ring (protoporphyrin IX complex) Heme non-covalently bound to globin proteins through proximal His residue O2 binds non-covalently to heme Fe++ and stabilized through H-bonding with another His residue (distal) 1 N His C His 64 E7 Distal F8 Proximal Heme group is present in hydrophobic pocket of globin protein When O2 binds, the electronic properties of heme iron change. This accounts for the change of color from dark purple of the deoxy form to the bright red of the oxy form In our lecture, we are going to discuss the different Oxygenation states of Hemoglobin. What an intelligent wise molecule. Deoxy hemoglobin (T form) Oxy hemoglobin (R form)... 3

4 Heme synthesis (Biochemistry) ILOs: By the end of this lecture, the student will be able to: 1. Have an overview on heme synthesis 2. Study regulation of heme synthesis Pre-requisite knowledge: - Before attending the lecture, please revise the previous lecture: (Heme structure & function) of Prof. Samar Kamal. - Please refer to Lippincott s illustrated Reviews, chapter 21 (Conversion of Amino Acids to Specialized Products). Heme is the prosthetic group for hemoproteins. These hemoproteins include: hemoglobin, myoglobin, cytochromes, catalase and tryptophan pyrrolase. Hemoproteins are rapidly synthesized and degraded. Heme is synthesized to replace heme lost through the normal turnover of erythrocytes. Heme is composed of iron in the ferrous state attached to the center of porphyrin ring. Porphyrins are cyclic compounds formed by the linkage of four pyrrole rings through 4 -HC= methenyl bridges Heme is an asymmetric molecule synthesized from glycine and succinyl-coa. It is catalyzed by ALA (delta-aminolevulinic acid) synthase in the presence of Pyridoxal phosphate (coenzyme of Vit B6). ALA synthase is the rate-controlling enzyme of Heme synthesis The major sites of heme biosynthesis are: The liver, which synthesizes a number of heme proteins ( particularly cytochrome P450 ) The erythrocyte producing cells of bone marrow, which are active in hemoglobin synthesis. Heme biosynthesis begins and ends in mitochondria, but 3 intermediate reactions occur in cytoplasm. The reactions are irreversible 4

5 Regulation of heme synthesis: Hemin inhibits synthesis of ALA synthase at gene level The activity of ALA synthase in liver (not in Bone marrow) can be increased by certain drugs. Hypoxia increases ALA synthase activity in bone marrow Lead has an inhibitory effect on ALA dehydratase & Ferrochelatase enzymes causes Sideroblastic anemia. Porphyria are rare group of genetic disorders of heme synthesis that have unfairly branded many sufferers with the term vampire ILOs: Iron Metabolism By the end of this lecture, the student will be able to: 1- Identify requirements and sources of iron. 2- Understand the absorption, transport, storage and excretion of iron. 3- Understand the regulation of iron metabolism. Pre-requisite knowledge Please refer to power point presentation of (Iron Metabolism) lecture of Prof. Dr. Maha Sallam Refer to (Human Iron Metabolism) From Wikipedia, the free encyclopedia. Human iron metabolism is the set of chemical reactions maintaining human homeostasis of iron at both the systemic and cellular level. The control of this necessary but potentially toxic metal is an important part of many aspects of human health and disease. Hematologists have been especially interested in systemic iron metabolism because iron is essential for red blood cells, where most of the human body's iron is contained. Understanding iron metabolism is also important for understanding diseases of iron overload, such as hereditary hemochromatosis, and iron deficiency, such as iron deficiency anemia. 5

6 Iron Metabolism includes : 1- Absorption (regulatory mucosal block) Factors affecting iron absorption 1. Requirements of body: An increase rate of erythropoiesis (e.g. after hemorrhage) 2. Vitamin C helps reduction of ferric to ferrous and forming soluble complex 3. Gastric HCl helps absorption, so absorption decrease in achlorhydria and partial gastrectomy 4. Some molecules in diet as tannic acid, phytate, phosphate and oxalates forming insoluble complexes with iron. 2- Transport 3- Cellular absorption (transferrin cycle) 4- Storage ( ferritin and hemosiderin) 5- Excretion Normally the body guards its own iron content and there is no physiological excretory mechanism. Excretion of iron occurs only through the normal shedding of tissues. Pre-requisite knowledge -Please refer to power point presentation of (Iron Metabolism ) lecture of Prof. Dr. Maha Sallam -Refer to (Human Iron Metabolism) From Wikipedia, the free encyclopedia. Human iron metabolism is the set of chemical reactions maintaining human homeostasis of iron at both the systemic and cellular level. The control of this necessary but potentially toxic metal is an important part of many aspects of human health and disease.hematologists have been especially interested in systemic iron metabolismbecause iron is essential for red blood cells, where most of the human body's iron is contained. Understanding iron metabolism is also important for understanding diseases of iron overload, such as hereditary hemochromatosis, and iron deficiency, such as iron deficiency anemia.. 6

7 Molecular biology of globin synthesis (Biochemistry) ILOs: by the end of this lecture, you will be able to: 1. Understand what is meant evolution in molecular biology and apply it to the evolution of hemoglobin. 2. Define the process of protein assembly, and apply this definition on hemoglobin 3. Explain how & why different types of hemoglobin are present. 4. Apply the previous knowledge to explain how genetic defects can produce different types of anemia of genetic origin. The globins are a family of globular proteins, which are thought to share a common ancestor. These proteins all incorporate the globin fold, a series of eight alpha helical segments. Two prominent members of this family include myoglobin and hemoglobin, which both bind the heme prosthetic group. Both of these proteins are reversible oxygen binders. Globins are heme-containing proteins involved in binding and/or transporting oxygen. The following is the hypothesized story of globin evolution over lifetime: 7

8 Globins originated first as one gene in one chromosome. As many genes, different types of mutations occurred so that globin gene underwent some molecular events to produce the current diversity of the polypeptide chains present now. First, a duplication process occurred to this gene on the same chromosome to produce two identical copies of the gene. Mutations occurred to both genes so that some dis-similarity between them occurred, however because they are still has more than 95% similarity in their amino acid sequence, they are still expressing proteins that have the same molecular structure (alpha helices folded the same way). They are now called α globin gene, and β globin gene. A molecular event called transposition occurred so that these two copies of the gene became on two different chromosomes (chromosome 11 and chromosome 16). Overtime (again and again), further duplication and mutation events occurred so that many versions of these globin genes arose (γ, δ & ε). These genes -as all eukaryotic genes- are having the same expression steps of transcription, mrna processing, and translation Please look in our textbook, chapter 3 (globular proteins) pages 34, & 35 at organization of the globin genes. These genes functioned in oxygen transfer in different organisms after being conjugated with the iron binding non-globin structure heme. Different combinations of these gene varieties occurred (over lifetime) but only the combinations that were successful in maintaining the life of their harboring organisms stayed in nature. Furthermore, in many different stages of life, some combinations were more successful than others in performing the required function of hemoglobin, that is why we find different types of hemoglobin in different embryological stages of humans till we reached the type known as adult hemoglobin. Please refer to our first lecture for types of hemoglobin. Now, try to think how further mutations in these genes can result in anemia of genetic origin to be discussed in the lecture. 8

9 ================================================================ ILOs Hemoglobinopathies (Biochemistry) By the end of this lecture the student will be able to: 1. Describe the different types of genetic defects the produce anemia. 2. Make a valid comparison between point mutation in sickle cell anemia and gene under-expression or gene deletion in thalassemia. These topics will be covered in the lecture, you can read more details in our textbook Chapter 3, page Mutations in α- or β- globin genes can cause disease state as Sickle cell anemia and thalassemia. 1. Sickle cell anemia: Sickle cell anemia is an Autosomal Recessive disease in which a mutation occurs in b- chain: E6 (polar negatively charged Glutamic Acid) to V6 (hydrophobic Valine) Valine as a hydrophobic amino acid will bind to hydrophobic pocket in deoxy-hb This type of hemoglobin is called Hemoglobin S HbS Polymerizes to form long filaments It causes sickling of cells Sickle cell anemia offers advantage against malaria Fragile sickle cells can not support parasite Normal Trait Anemia - Hb S Hb A + Diagnosis of sickle cell anemia by electrophoresis 9

10 2. Thalassemias Decreased rate of synthesis of globin chains -Thalassemias: decrease rate of synthesis of -globin chains. -Thalassemias: decrease rate of synthesis of -globin chains. or chains will increase. We discussed in our last lecture that there are many copies of the globin gene are present. For the gene, for copies are present, that is why there are several levels of the disease state that originate from deletion mutation of these gene copies. Because the presence of at least one globin chain is essential for the hemoglobin to carry its function, the deletion of the 4 genes is incompatible with life. Deletion of three copies will result in only ¼ of the hemoglobin molecules are efficient in oxygen transport, the so called hemoglobin H disease. It is severe condition of hemolytic anemia demanding life-long blood transfusions. Deletion of two copies, this will be an thalassemia trait, in which the person may be asymptomatic, however his offspring may develop more severe disease if another affected gene came from the other parent. Deletion of only one copy of the four genes will result in a silent carrier state. Figure 3.23, page 39 will demonstrate this in more clearly. Other types of hemoglobinopathies Hb M: substitution of proximal histidine by tyrosine causing oxidation of Fe ++ to Fe +++ forming methemoglobin Hb C: substitution of two glutamate residues in the chain by lysine casing Mild hemolytic anemia ================================================================= ======== 10

11 RBCs Metabolism Glycolysis (Biochemistry) By the end of this lecture, you will be able to: 1. Know how glucose is transported to inside the cells. 2. Understand the importance of the glycolytic pathway. 3. Understand the glycolytic reactions in sequence. 4. Make a valid comparison between tissues that contain mitochondria and tissues that don t regarding energy production. 5. Retrieve how glycolysis is the sole source of energy to RBCs. 6. Understand how RBCs can get the hemoglobin negative allosteric effector 2,3, BPG from glycolysis. 7. Know that pyruvate kinase deficiency can cause hemolytic anemia. Prerequisite to these two lectures: Please refer to last year Biochemistry lecture 28 (glucose metabolism). In these two lecture, we will discuss the different glycolytic reactions and know the specific reactions that produce not only energy to RBCs but also important metabolites that are important in controlling oxygen delivery to tissues from hemoglobin. You can enjoy the demonstrations and figures in our textbook Chapter 8 page Glycolysis is a series of biochemical reactions by which glucose is converted to: Pyruvate (in aerobic conditions) or Lactate (in anaerobic conditions). Site: Cytosol of every cell. It is the sole source of energy to the cells missing the mitochondria as RBCs. Steps: it has two phases. Phase one: In this phase 1 molecule of glucose (C6) is converted to 2 molecules of glyceraldehydes 3-phosphate (C3) as follows: ATP ATP Glucose (C6) 2 Glyceraldehyde 3 P (C3). These steps actually require energy, in the form of two ATPs per glucose molecule. Phase two: 11

12 In this phase the 2 molecules of glyceraldehydes 3-p are converted to 2 molecules of lactate (anaerobic): Overall, glycolysis can thus be summarized as follows: Glucose: - 2 pyruvic Acid + 2 net ATP + 4 Hydrogen (2 NADH + + H + ) in cells that have mitochondria, and 2 Lactic Acid + 2 net ATP (anaerobic conditions) in cell that don t have mitochondria as RBCs. The detailed reactions of this pathway will be explained in two lectures. Figures 8.9. page 96, 8.22, page 104 and figure 8.23 page 105 in our text will make it more clear. Useful animation: nimation how_glycolysis_works.html Lecture 12 {Thursday 29/9/2016, 10:30 am} HMP pathway By the end of this lecture, you will be able to: 1. Know that there are other glucose oxidative pathways that have specific functions. 2. Understand the importance of NADPH production to RBCs. 3. Understand how glutathione can keep the integrity of RBCs membrane. 4. Retrieve how an enzyme deficiency can cause hemolytic anemia. The pentose phosphate pathway is a metabolic pathway parallel to glycolysis that generatesnadph and pentoses (5-carbon sugars). While it does involve oxidation of glucose, its primary role is anabolic rather than catabolic. There are two distinct phases in the pathway. The first is the oxidative phase, in which NADPH + is generated. The second is the non-oxidative synthesis of 5-carbon sugars. The pentose phosphate pathway takes place in the cytosol. 12

13 The primary results of the pathway are: The generation of reducing equivalents, in the form of NADPH +, One of the uses of NADPH + in the cell is to prevent oxidative stress. It reduces glutathione via glutathione reductase, which converts reactive H 2 O 2 into H 2 O by glutathione peroxidase. If absent, the H 2 O 2 would be converted to hydroxyl free radicals, which can disrupt the cell membrane. Erythrocytes generate a large amount of NADPH + through the pentose phosphate pathway to use in the reduction of glutathione. Hydrogen peroxide is also generated for phagocytes in a process often referred to as a respiratory burst. Our lecture will explain the cycle in details. Chapter 13 will be our reference for more understanding. 13

14 It is nice to read the summary of RBCs metabolism at this website: 14

15 Folic acid & B12 metabolism (Biochemistry) By the end of this lecture, you will be able to: 1. Understand that vitamins are important nutrients that are important to health. 2. Know that folic acid and vitamin B12 are the hematopoitic vitamins. 3. Understand how vitamin B12 is important in the activation of folic acid. 4. Understand why deficiencies of both of them produce the same type of anemia. 5. Understand why B12 deficiency results in neurological manifestations. This lecture will cover these items, however you can go back to your textbook chapter 28, pages for more understanding. Folic acid (folacin) Folic acid or folate consists of the base pteridine attached to one molecule of each p-aminobenzoic acid (PABA), and glutamic acid. 15

16 Animals are not capable of synthesizing PABA or attaching glutamic to pteridine. It must be supplied in diet. Liver, yeast and green leafy vegetables are the major sources. It is present as polyglutamate conjugate consisting of linked polypeptide chain of 2-7 glutamate residues. Metabolic role: The biologically active form is the tetrahydrofolate. It is the carrier of activated one carbon units that are essential for the synthesis of choline, serine, glycine, methionine and purines. Sulfa drugs inhibit synthesis of folic acid in bacteria (antibiotics). 16

17 Trimethoprim, and methotrexate are inhibitors of folate reductase (anticancer chemotherapeutic agents). Requirements: 400 g/day to be increased during pregnancy and lactation. Deficiency: It may occur due to increase demand, poor absorption, vitamin B12 deficiency, interference with metabolism of folic acid. Deficiency leads to Megaloblastic anemia. Folate trap 17

18 Vitamin B 12 Vitamin B12 has a complex tetrapyrrole ring structure (corrin ring) to which a cobalt ion is added to its center. Cobalt is essential for activity, it is the cause of the red color. Many groups can be attached to cobalt e.g. a methyl group (methylcobolamin), a hydroxyl group (hydroxycobolamin), CN (cyanocobolamin), or adenosyl group (adenosylcobolamin). Vitamin B12 Sources and absorption: Vitamin B12 is exclusively formed by microorganisms. It is absent from plant sources. In animals it is conserved in the liver as adenosylcobolamin, methylcobolamin or hydroxycobolamin. Liver and yeast are good sources. Intestinal absorption needs a highly specific glycoprotein receptor called intrinsic factor. After absorption it is transported bound to a plasma protein called transcobolamin. It is the only water soluble vitamin that is stored in the liver. Up to 6 years supply of B12 can be stored in the liver. Intracellularly, It is either converted in the cytosol to methylcobolamin, or it inters the mitochondria to be converted to 5 -deoxyadenosylcobolamin. 18

19 Metabolic functions: Deoxyadenosylcobolamin is the coenzyme for conversion of methylmalonyl CoA to succinyl CoA which is a member of the citric acid cycle. Methylcobolamin is the coenzyme in the combined conversion of (1) homocysteine to methionine, and (2) methyltetrahydrofolate to tetrahydrofolate. Deficiency: Vitamin B12 is rarely to be deficient. However some conditions are associated with its deficiency: Malabsorption (lack of the intrinsic factor) due to atrophy of gastric mucosa, achlorhydra, or after total gastrectomy. Debilitated patients. Vegetarian people. If plants are contaminated with microorganisms, supply of B 12 will be sufficient. 19

20 Deficiency Leads to a condition called pernicious anemia or megaloblastic anemia. This occurs due to Impaired DNA synthesis and prevention of cell division with the accumulation of immature erythrocytes in the circulation. Folate will be trapped as methyltetrahydrofolate (folate trap) will lead to impaired purine and pyrimidine synthesis. Neurological disorders are due to progressive demylination of nervous tissue. This may be secondary to deficiency of methionine leading to defective methylation. High levels of supplemental folate can overcome the megaloblastic anemia but not the neurological disorders. Hence caution must be utilized in using folate to treat megaloblastic anemia. ======================================================= 20

21 Role of vitamin K in blood coagulation (Biochemistry) By the end of this lecture, the student will be able to: 1. Identify the biochemical role of vit K in blood coagulation. Biochemical role of vit K: Vit K is necessary for blood coagulation. It regulates the hepatic synthesis of prothrombin and some other plasma clotting factors (II, VII, IX, and X). It helps the activation of pre-prothrombin into prothrombin through carboxylation of the carbon of glutamate residues in pre-prothrombin. Vitamin K Function 21

22 Glutamic acid Warfarin Ca ++ Ɣ-carboxyglutamic acid N.B. Gamma carboxylation reaction is competitively inhibited by warfarin and / or dicumarol. Warfarin and dicumarol are widely used as anticoagulants for therapeutic purposes as they inhibit carboxylation system. What are the Manifestations of vit K deficiency? =========================================================== 22

23 WBCs Metabolism By the end of this lecture, you will be able to: List the major metabolic pathways in neutrophils. Define the free radicals. List the reactive oxygen species (ROS). Define the oxygen burst Understand the function of different enzymes involved in production and scavenging of ROS. Understand the regulation of proteinase activity. Know how anti-proteinase deficiency cause disease. Neutrophils Have An Active Metabolism The major biochemical features of neutrophils are: Active aerobic glycolysis. Active pentose phosphate pathway. Moderately active oxidative phosphorylation (because mitochondria are relatively few). High content of lysosomal enzymes. Contain certain unique enzymes as myeloperoxidase and NADPH oxidase. Neutrophils Are Key Players in the Body s Defense Against Bacterial Infection Neutrophils are motile phagocytic cells of the innate immune system that play a key role in acute inflammation. When bacteria enter tissues, a number of phenomena result that are collectively known as the acute inflammatory response. They include: (1) Increase of vascular permeability. (2) Entry of activated neutrophils into the tissues. (3) Activation of platelets. (4) Spontaneous subsidence (resolution) if the invading microorganisms 23

24 have been dealt with. One of the mechanisms of dealing with microorganisms is production of reactive oxygen species. Free radicals OR Reactive oxygen species (ROS): Several powerful oxidants are produced during the course of metabolism, in both blood cells and most other cells of the body. These include superoxide (O2 ), hydrogen peroxide (H2O2), peroxyl radicals (ROO ), and hydroxyl radicals (OH ) are referred to as reactive oxygen species (ROS). Superoxide configuration Free radicals are atoms or groups of atoms that have an unpaired electron. They can react with proteins, nucleic acids, lipids, and other molecules to alter their structure and produce tissue damage. ROS are thought to play an important role in many types of cellular injury (eg, resulting from administration of various toxic chemicals or from ischemia), some of which can result in cell death. Several reactions play an important role in forming these oxidants and in disposing of them: (1) Reaction 1: Superoxide (O2 ) is formed in the red blood cell by the auto-oxidation of hemoglobin to methemoglobin (about 3% daily). In other tissues, it is formed by the action of enzymes such as cytochrome P450 reductase and xanthine oxidase. (2) Reaction 2: When stimulated by contact with bacteria, neutrophils 24

25 exhibit a respiratory burst and produce superoxide in a reaction catalyzed by NADPH oxidase. NADPH + 2O2 NADP + + 2O2 + H + The NADPH is generated mainly by the pentose phosphate cycle, whose activity increases markedly during phagocytosis. (3) Reaction 3: Superoxide spontaneously dismutates to form H2O2 and O2. However, the rate of this same reaction is speeded up tremendously by the action of the enzyme superoxide dismutase (SOD). (4) Reaction 4: Hydrogen peroxide H2O2 is subject to a number of fates. The enzyme catalase, present in many types of cells, converts it to H2O and O2. (5) Reaction 5: Neutrophils possess a unique enzyme, myeloperoxidase 25

26 that uses H2O2 and halides to produce hypohalous acids (HOCl). (6) Reaction 6: The selenium-containing enzyme glutathione peroxidase will also act on reduced glutathione (GSH) and H2O2 to produce oxidized glutathione (GSSG) and H2O; this enzyme can also use other peroxides as substrates. 26

27 (7) Reaction 7: OH, and OH can be formed from H2O2 in a non-enzymatic reaction catalyzed by Fe 2+ (the Fenton reaction) (READING ONLY). (8) Reaction 8: O2 and H2O2 are the substrates in the iron-catalyzed Haber-Weiss reaction, which also produces OH and OH. Superoxide can release iron ions from ferritin. Thus, production of OH may be one of the mechanisms involved in tissue injury due to iron overload in hemochromatosis (READING ONLY). 27

28 Oxidative stress: Chemical compounds and reactions capable of generating potential toxic oxygen species can be referred to as pro-oxidants. On the other hand, compounds and reactions disposing of these species, scavenging them, suppressing their formation, or opposing their actions are antioxidants and include compounds such as NADPH, GSH, ascorbic acid (vitamin C), and vitamin E. In a normal cell, there is an appropriate pro-oxidant: antioxidant balance. However, this balance can be shifted toward the pro-oxidants in the following conditions: Increased production of oxygen species (eg, following ingestion of certain chemicals or drugs. The state of diminished levels of antioxidants by inactivation of enzymes involved in disposal of oxygen species, and by conditions that cause low levels of them is called oxidative stress and can result in serious cell damage if the stress is massive or prolonged. When neutrophils and other phagocytic cells engulf bacteria, they exhibit a rapid increase in oxygen consumption known as the respiratory burst. This phenomenon reflects the rapid utilization of oxygen (following a lag of seconds) and production from it of large amounts of reactive derivatives, such as O2, H2O2, OH, and OCl (hypochlorite ion). Some of these products are potent microbicidal agents. 28

29 Phagocytosis and the oxygen-dependent pathway of microbial killing Neutrophils Contain Myeloperoxidase, Which Catalyzes the Production of Chlorinated Oxidants 29

30 The enzyme myeloperoxidase is present in large amounts in neutrophil granules. It is responsible for the green color of pus, can act on H2O2 to produce hypohalous acids (hypochlorite): Cl is the halide usually employed, since it is present in relatively high concentration in plasma and body fluids. HOCl, the active ingredient of household liquid bleach, is a powerful oxidant and is highly microbicidal. When applied to normal tissues, its potential for causing damage is diminished because it reacts with some amines present in neutrophils and tissues to produce chloramines, which are also oxidants, though less powerful than HOCl. Any superoxide that enters the cytosol of the phagocytic cell is converted to H2O2 by the action of superoxide dismutase, which catalyzes the same reaction as the spontaneous dismutation. In turn, H2O2 is used by myeloperoxidase or disposed of by the action of glutathione peroxidase or catalase. 30

31 Mutations in the Genes for Components of the NADPH Oxidase System Cause Chronic Granulomatous Disease The importance of the NADPH oxidase system was clearly shown when it was observed that the respiratory burst was defective in chronic granulomatous disease, a relatively uncommon condition characterized by recurrent infections and widespread granulomas (chronic inflammatory lesions) in the skin, lungs, and lymph nodes. The disorder is due to mutations in the genes encoding the NADPH oxidase system. Sequence of events involved in the causation of chronic granulomatous disease The Proteinases of Neutrophils Can Cause Serious Tissue Damage if Their Actions Are Not Checked Neutrophils contain a number of proteinases that can hydrolyze elastin, various types of collagens, and other proteins present in the extracellular matrix. 31

32 Such enzymatic action, if allowed to proceed unopposed, can result in serious damage to tissues. Most of these proteinases are lysosomal enzymes and exist mainly as inactive precursors in normal neutrophils. Small amounts of these enzymes are released into normal tissues, with the amounts increasing markedly during inflammation. The activities of elastase and other proteinases are normally kept in check by a number of antiproteinases present in plasma and the extracellular fluid. Each of them can combine usually forming a non-covalent complex with one or more specific proteinases and thus cause inhibition. Genetic deficiency of α1-antiproteinase inhibitor (α1-antitrypsin) permits elastase to act unopposed and digest pulmonary tissue, thereby participating in the causation of emphysema. Some Proteinases of Neutrophils and Anti-proteinases of Plasma and Tissues When increased amounts of chlorinated oxidants are formed during inflammation, they affect the proteinase: anti-proteinase equilibrium, tilting it in favor of the former. Assigned Task: Anti-proteinase deficiency can produce serious diseases. Give an illustrated example describing how this occurs. ============================================== Enjoy 32