PROTEIN METABOLISM DEPT OF BIOCHEMISTRY ACS MEDICAL COLLEGE CHENNAI - 77

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1 PROTEIN METABOLISM DEPT OF BIOCHEMISTRY ACS MEDICAL COLLEGE CHENNAI - 77

2 DIGESTION & ABSORPTION

3 DIETARY PROTEINS SERVE 3 FUNCTIONS 1. THEIR CONSTITUTENT AMINOACIDS ARE USED FOR SYNTHESIS OF BODY PROTEINS 2. THE CARBON SKELETONS OF THE AMINO ACIDS ARE OXIDISED TO YIELD ENERGY 3. THEIR CARBON & NITROGEN ATOMS MAY BE USED TO SYNTHESISE OTHER N CONTAINING CELLULAR CONSTITUENTS AS WELL AS MANY NON- NITROGEN CONTAINING METABOLITES

4 DIGESTION TAKES PLACE WITH THE HELP OF ENZYMES SECRETED BY 1. STOMACH 2. PANCREAS 3. SMALL INTESTINE

5 1.DIGESTION IN STOMACH ENTERING PROTEINS (+) GASTRIN (+) GASTRIC JUICE (ph ) CONTAINING 1. HCL 2. PEPSINOGEN 3. RENNIN (IN INFANTS)

6 HYDROCHLORIC ACID SECRETED BY PARIETAL CELLS KILLS MICRO-ORGANISMS DENATURES PROTEIN MAKING INTERNAL PEPTIDE BONDS MORE SUSCEPTIBLE TO SUBSSEQUENT HYDROLYSIS BY PROTEOSES PROVIDES ACID ENVIRONMENT FOR PEPSIN ACTION

7 PEPSIN SECRETED BY CHIEF CELLS AS PEPSINOGEN INACTIVE PRECURSOR CONVERTED TO ACTIVE PEPSIN BY AUTOCATALYSIS WORKS AT ACIDIC ph CLEAVES PEPTIDE BONDS INVOLVING AROMATIC & ACIDIC AA

8 PEPSINOGEN PEPSIN PEPSIN H + (ph ) DIETARY PROTEIN SMALLER PEPTIDES + AA

9 RENNIN CHYMOSIN / RENNET IMPORTANT IN INFANTS DIGESTIVE PROCESS CLOTTING OF MILK R Ca ++ CASEIN PARACASEIN Ca ++ PARACASEINATE THE PURPOSE OF THIS REACTION IS TO CONVERT MILK INTO MORE SOLID FORM TO PREVENT THE RAPID PASSAGE OF MILK FROM STOMACH OF INFANTS

10 2.DIGESTION IN INTESTINE BY PANCREATIC ENZYMES ACIDIC CONTENTS (CHYME) PASSING INTO SMALL INTESTINE TRIGGERS THE SECRETION OF 1. SECRETIN 2. CHOLECYSTOKININ

11 SECRETIN STIMULATES PANCREAS TO SECRETE BICARBONATE & RELEASE OF PANCREATIC JUICE INTO THE SMALL INTESTINE. NEUTRALISES GASTRIC HCL CHANGING ph FROM

12 CHOLECYSTOKININ STIMULATES SECRETION OF PANCREATIC ENDOPEPTIDASE & EXOPEPTIDASE ENDOPEPTIDASE INCLUDES CHYMOTRYPSIN & ELASTASE, CLEAVING INTERNAL PEPTIDE BONDS EXOPEPTIDASE CLEAVES 1 AA AT A TIME FROM EITHER C OR N END. INCLUDES CARBOXYPEPTIDASE & AMINOPEPTIDASE

13 ACTIVATION OF PANCREATIC PRO-ENZYMES TRYPSINOGEN ENTEROPEPTIDASE TRYPSIN CHYMOTRYPSINOGEN CHYMOTRYPSIN PRO-ELASTASE ELASTASE PROCARBOXYPEPTIDASE CARBOXYPEPTIDASE

14 TRYPSIN HYDROLYSES PEPTIDE BONDS WHOSE CRBOXYL GROUPS ARE CONTRIBUTED NY LYS & ARG RESIDUES CHYMOTRYPSIN-CLEAVES PEPTIDE BONDS INVOLING CARBOXYL GROUP OF AROMATIC AA ELASTASE HYDROLYSES THOSE PEPTIDE BONDS FORMED BY SMALL NON- POLAR AA RESIDUES SUCH AS ALA, SER & GLY THUS 3 ENZYMES HYDROLYSE POLYPEPTIDES TO SMALLER PEPTIDES

15 Degradation of short peptides in the small intestine is continued by an EXOPEPETIDASE- CARBOXYPEPTIDASE which removes the successive carboxy terminal aa residues from peptide 1. CARBOXYPEPTIDASE A RELEASES HYDROPHOBIC AA 2. CARBOXYPEPTIDASE B RELEASES BASIC AA

16 3.DIGESTION IN INTESTINE BY INTESTINAL PROTEOSES The digestion is completed by the PEPTIDASES of the mucosa of the small intestine namely: 1. AMINOPEPTIDASES 2. GROUP OF DIPEPTIDASES

17 AMINO-PEPTIDASE - EXOPEPTIDASE - REQUIRE Mg/Mn - HYDROLYSE PEPTIDE BONDS NEXT TO N-TERMINAL AA OF SHORT PEPTIDES DIPEPTIDASES - COMPLETE THE DIGESTION OF DIPEPTIDES TO FREE AMINO ACIDS

18 ABSORPTION OF AMINOACIDS MOSTLY THRU ACTIVE TRANSPORT 5 SEPARATE SYSTEMS TRANSPORT L- AMINOACIDS FROM INTESTINAL LUMEN INTO INTESTINAL EPITHELIAL CELLS THUS AA RELEASED BY DIGESTION PASS FRM GUT THRU HEPATIC PORTAL VEIN TO THE LIVER TRANSPORT SYSTEM ALSO PRESENT IN RENAL SYSTEM

19 TRANSPORT SYSTEM Small neutral aminoacids Large neutral aminoacids Basic aa & Cysteine Acidic aminoacids Iminoacid, Glycine AMINOACID TRANSPORTD Ala Ser & Thr Isoleu, Leu, Val,Tyr,Trp,Ph e Arg, Lys, Ornithine, Cys Glutamic acid Aspartic acid Pro, Hydroxy pro, Gly DISORDER HARTNUP Disease CYSTINUTIA GLYCINURIA

20 MEISTER CYCLE GAMMA GLUTAMYL CYCLE AMINO ACID GLUTATHIONE GLUTAMYL AMINOACID CYSTEINYL GLYCINE AMINOACID GLYCINE CYSTEINE GLUTAMYL-CYSTEINE OXOPROLINE GLUTAMATE

Day Date Title Instructor 5 th Ed 6 th Ed. Protein digestion and AA absorption

Day Date Title Instructor 5 th Ed 6 th Ed 1 Tuesday 18 April 2017 Protein digestion and AA absorption D S Jairajpuri 250 256 250 256 2 Wednesday 19 April 2017 Removal of nitrogen and urea cycle D S Jairajpuri