Midterm 2 Results. Standard Deviation:

Transcription

1 Midterm 2 Results High: Low: Mean: Standard Deviation: 97.5% 16% 58% 16.3

2 Lecture 17 Amino Acid Metabolism Urea Cycle N and S assimilation Last cofactors: THF and SAM

3 Dietary (Exogenous) Proteins Hydrolyzed in digestive system (~100 g/day) Replenish endogenous amino acids (muscle protein) Replenish glycogen stores (glucogenic amino acids) Excess intake for ATP production and lipid synthesis Excess nitrogen is excreted (urea, ammonia) Nitrogen balance is typically zero

4 Dietary Protein Proteases, Peptidases (e.g., Trypsin,, Pepsin) Amino Acids Blood Liver Hepatocytes (Cytosol) Amino Acid x Aminotransferases (PLP-dependent) + -KGA -Keto Acid x + Glu From and To Mitochondria

5 From cytosol Hepatocytes Glu Dehydrogenase Glu + NAD + + H 2 -KGA + NADH + NH 3 Asp Aminotransferase Glu + AA -KGA + Asp Mitochondria To cytosol

6 Synthesis of Urea from Ammonia and Aspartate The Urea Cycle James Sumner (1926) Freiedrich Wöhler (1828) Urease Sir Hans Krebs Urea Cycle (1932) TCA Cycle (1937)

7 Detoxification of ammonia GLU + NAD H KGA + NADH + H NH 3 NH 3 + HC ATP ADP + HP P C NH 2 Carbamoyl-P p. 88

8 2-3 P C NH 2 3 The Urea Cycle NH 2 C HP 4 3- NH Citrulline rnithine H H 2 NH 2 C C - NH H 2 N UREA C NH 2 H C C - NH ATP Aspartate AMP + PPi Arginine H 2 N H C NH 2 + NH C C - NH 3 + C - HC CH C - 5 Fumarate HN C NH H C C - NH 3 + NH 2 + C - CH C - Argininosuccinate p. 88

9 Carbamoyl-P Synthetase NH 3 + HC ATP Carbamoyl amoyl-p + 2ADP + Pi Carbamoyl amoyl-p H 2 N-Asp rnithine Urea Cycle Fumarate Malate AA H 2 N C NHNH 2 Mitochondria and Cytosol

10 Amino Acids C-Skeletons NADH -KGA AA NADH Glu Dehydrogenase Asp Aminotransferase NAD + Glu NAD + NH + 4 Asp Malate Urea Cycle Fumarate H 2 N C NH 2 HC 3 - UCD: Urea Cycle Disorders

11 Urea Cycle Net Reaction ATP Requirement NH 3 + HC Asp + 3ATP Urea + Fumarate + 2ADP + AMP + 4Pi (4 P~bonds cleaved = 44 ATP ) But NADH Generation Glu + NAD + + H 2 -KGA + NADH + NH 3 Malate + NAD + AA + NADH 6 ATP (ETC) Net Gain of 2ATP/Urea

12 Endogenous Proteins A. Normal Protein Turnover ( g/day) Digestive enzymes (pancreas: >30 g/day) Plasma proteins Cell death (e.g., intestinal mucosa, immune system) Intracellular turnover (damaged proteins, enzyme regulation) B. Mobilization of Skeletal Muscle Protein Fasting, exercise, trauma, injury Gluconeogenesis Malnutrition (diets deficient in essential amino acids)

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14 Skeletal Muscle Intracellular Proteolysis Amino Acids Amino Acid x Aminotransferases + -KGA -Keto Acid x + Glu Ala Aminotransferase Glu + Pyr -KGA + Ala To Liver

15 Skeletal Muscle Intracellular Proteolysis Amino Acids Amino Acid x Aminotransferases + -KGA -Keto Acid x + Glu Glu Dehydrogenase Glu + NAD + + H 2 -KGA + NADH + NH 3 Glutamine Synthetase NH 3 + Glu + ATP ADP + Pi + Gln To Liver To Kidneys

16 Liver Ala Aminotransferase Ala + -KGA Glu + Pyr Glucose Glutaminase NH 3 or Asp Gln + H 2 Glu + NH 3 Urea Kidneys Glutaminase Gln + H 2 Glu + NH 3 Urine

17 Muscles (other extrahepatic organs) B L D Ala Gln In conditions of metabolic acidosis Liver Urea Kidneys NH 3 HC - 3 Urea

18 The Cori and Alanine Cycle Glycogen Glucose Pyruvate Proteins Muscle Lactate Alanine Blood Liver Lactate Alanine Glycogen Glucose Pyruvate Urea p. 89

19 Degradation of Amino Acids: Fate of C-Skeletons Glucogenic Amino Acids: C-skeletons are converted to Pyruvate -Ketoglutarate Succinyl-CoA Fumarate xaloacetate (AA) Ketogenic Amino Acids: C-skeletons are converted to Acetyl-CoA Acetoacetate p. 90

20 Glucose Pyruvate Glucogenic Acetyl-CoA Ketogenic Lipids Ketone Bodies xalaoacetate Citrate Malate TCA Cycle Isocitrate Fumarate -Ketoglutarate Succinyl-CoA

21 Amino Acids Common Degradation Product nly glucogenic Ala, Cys, Gly, Ser, Thr Asp, Asn Met, Thr (humans), Val Arg, Glu, Gln, His, Pro Pyruvate AA Succinyl-CoA -Ketoglutarate nly ketogenic Leu, Lys Acetoacetate Ketogenic and glucogenic Phe, Tyr Trp Ile Fumarate, Acetoacetate Pyruvate, Acetyl-CoA Succinyl-CoA CoA, Acetyl-CoA p. 90

22 Nitrogen and Sulfur Assimilation (Amino Acid Synthesis)

23 Nitrogen and Sulfur Assimilation (Amino( Acid Biosynthesis) LIGHT 2 ATP NADPH C 2 N 3-, N 2 S 43 - Photosynthesis NADP + ADP + Pi H 2 Carbohydrates Amino Acids Light Reactions C 2 Fixation p. 91

24 Bioenergetics of Macronutrient Assimilation Electronegativity Assimilation (3.4) N (3.0) S (2.6) C (2.6) - N 3 2- S 4 C 2 NAD(P)H NAD(P)H + ATP NAD(P)H + ATP NH 3 H 2 S CH Photosynthesis H (2.2) H 2 (H 2 ) P (2.1) P 4 3- PH 3

25 Nitrate Assimiliation and Nitrogen Fixation A. Most Microorganisms, Fungi, and Plants Nitrate Reductase N NADH + H + N NAD + + H 2 Nitrite Reductase N Fd red + 8 H + NH H Fd ox B. Biological Nitrogen Fixation (Microorganisms) Nitrogenase N 2 + 8e H ATP + 16 H 2 2 NH ADP + 16 Pi + H 2 p. 91

26 Assimilation of Ammonia Major Pathway for Ammonia Net Assimilation (M, Fungi, Plants) Glutamine Synthetase (GS) NH 3 + Glu + ATP Gln + ADP + Pi Glutamate Synthase Gln + -KGA + NAD(P)H + H + 2 Glu + NAD(P) + Glutamate Aminotransferase (also present in animals) Glu + -Keto Acid -KGA + L- -Amino Acid Glutamine Amidotransferase (also present in animals) Gln + R-H or R 1 -(C=)-R 2 Glu + R-NH 2 or R 1 -(C=NH)-R 2 p. 92

27 Sulfur Assimilation S 4 2- S P H H H H H H Adenosine monophosphate sulfate (APS) Adenine carrier AMP carrier-s-s 3-6 Reduced Ferredoxin 6 xidized Ferredoxin 2Fdox 2Fdred HS CH C H carrier-s-s - NH 2 Cysteine Acetate H 3 C C CH C H H NH 2 -acetyl serine p. 95

28 Sulfur Assimilation 2 Cysteine Acetate H 3 C C CH C H H NH 2 -acetyl serine Pi C C H 3-Phosphoglycerate (3PGA) H NAD + CoA NADH + H + Acetyl CoA Pi C C H Glu Pi KG CH NH 2 C H H 2 Pi H CH NH 2 C H Hydroxy-P-pyruvate -phospho-serine Serine p. 95