Metabolism-of-Proteins in the body of eukaryotes.pptx

proteolysis

1. Metabolism of Proteins Roshan Ali Assistant Professor IBMS, KMU

2. Course Contents Metabolism of Protein Review the digestion and absorption of Proteins Nitrogen balance General pathway of Protein metabolism De-amination

3. Digestion and Absorption of Proteins 3 Biochemistry for Medics

4. Digestion is the disintegration of complex nutrients into simple, soluble and assimilable form. Most of the nitrogen in the diet is consumed in the form of proteins. Proteins are too large to be absorbed. The dietary proteins are hydrolyzed to amino acids by proteolytic enzymes, which can be easily absorbed. 4 Biochemistry for Medics Digestion of dietary proteins

5. Proteolytic enzymes responsible for degrading proteins are produced by three different organs; stomach , pancreas small intestine. Biochemistry for Medics 5

6. 1)The y are hydrolases. 2)Secreted in the zymogen (Inactive) form , converted to active form in the intestinal lumen. The active site of the enzyme is masked by a small region of the peptide chain that is removed by hydrolysis of a specific peptide bond. 3) They may be Exopeptidases or Endopeptidases. Exopeptidases catalyze the hydrolysis of peptide bonds , one at a time, from the ends of peptides. Endopeptidases hydrolyze peptide bonds between specific amino acids throughout the molecule. Characteristics of proteolytic enzymes 6 Biochemistry for Medics

7. There are no proteolytic enzymes present in the saliva . The function of the saliva is to lubricate the food, this helps in making food soluble for the action of proteolytic enzymes. After mastication and chewing, the bolus of food enters stomach where it is acted upon by gastric juice. Digestion in the oral cavity 7 Biochemistry for Medics

8. Gastric juice contains HCL and 4 proteolytic enzymes: Pepsin , Rennin , Gastriscin and Gelatinase . Digestion by gastric juice 8 Biochemistry for Medics

9. Functions of HCL Too dilute to hydrolyze but can cause denaturation of dietary proteins - Required for activation of inactive proteolytic enzymes secreted by the gastric mucosa. - Has a strong bacteriostatic action. Biochemistry for Medics 9

10. -Secreted in the form of pepsinogen, activated by HCL and pepsin itself (Autocatalysis) - Acid stable endopeptidase, optimum pH lies between 1.6-2.5 ; becomes inactive if the pH is > 5.0 - Active for a peptide bond where amino group is contributed by aromatic amino acids like Phenyl Alanine, Tyrosine and Tryptophan. Functions of Proteolytic enzymes Pepsin 10 Biochemistry for Medics

11. - Present in infants but absent in adult gastric juice. - Secreted as pro-rennin -Optimum p H 4.0 -Action is similar to pepsin -Acts on casein of milk and is involved in the curdling of milk -Commercially , ‘rennet’ tablets are used in the making of cheese. Functions of proteolytic enzymes Rennin 11 Biochemistry for Medics

12. -Both are secreted in zymogen form and are acid-stable. Activated in the presence of HCL. -Gelatinase acts on Gelatin to hydrolyze it to short peptides. Functions of proteolytic enzymes Gastriscin and Gelatinase 12 Biochemistry for Medics

13. The bolus of food after leaving stomach reaches duodenum and is acted upon by the pancreatic juice. All the enzymes are active only in the alkaline medium and alkalinity is provided by Bile juice and bicarbonates present in pancreatic juice. The proteolytic enzymes present in pancreatic juice are: -Trypsin -Chymotrypsin -Elastase -Collagenase - Carboxypeptidases Digestion by Pancreatic Juice 13 Biochemistry for Medics

14. Role of Trypsin 14 Biochemistry for Medics -Secreted in the zymogen form (Trypsinogen) and activation is brought about by Enterokinase (secreted by the intestinal mucosa ) and by Trypsin itself. Trypsin is specific for cleaving peptide bonds contributed by basic amino acids. Required for activation of Chymotrypsin Required for conversion of pro- elastase to elastase It is required for conversion of fibrinogen to fibrin It has weak action on casein

15. - Activated by Trypsin and Chymotrypsin itself (auto catalytically ) -Cleaves peptide bonds contributed by aromatic amino acids. - Can hydrolyze milk protein. Role of Chymotrypsin 15 Biochemistry for Medics

16. Two types of Carboxypeptidase are there Carboxypeptidase A :Metalloenzyme , contains Zinc, Activation brought about by Trypsin and auto catalytically by itself, Exopeptidase, Hydrolyzes the terminal peptide bond connected to an end amino acid (Aromatic) bearing free carboxyl group Carboxypeptidase B : Also an Exopeptidase, hydrolyzes terminal peptide bonds connected by basic amino acids Role of Carboxy-peptidases 16 Biochemistry for Medics

17. Elastase- Activated by Trypsin Has maximum activity on peptide bonds contributed by carbonyl groups of neutral aliphatic amino acids- Alanine, Glycine, Serine etc. Collagenase- Acts on Collagen Role of Elastase and Collagenase 17 Biochemistry for Medics

18. 18 Biochemistry for Medics

19. Enzymes present in intestinal juice are: - Enterokinase - Amino peptidases - Prolidase - Di and Tri peptidases Digestion by intestinal Juice 19 Biochemistry for Medics

20. Enterokinase - required for activation of Trypsin, also called Enteropeptidase, present in the epithelial cells of brush border of duodenal mucosa. Bile salts help in its liberation in to intestinal lumen. Amino peptidases – are exopeptidases , remove the amino acid one by one from amino terminal end of peptide chains. Prolidase - also an exopeptidase, removes proline residues from terminal end of peptide chains. Functions of the Intestinal enzymes 20 Biochemistry for Medics

21. Di and Tripeptidases - Digestion of di and tri peptides is brought about by di and tri peptidases present in brush border membrane of epithelial cells as well as present in the interior of the cell. Tripeptidases convert tripeptides into a dipeptide and a free amino acid, then dipeptidases convert dipeptides to free amino acids. Functions of Intestinal enzyme(Contd.) 21 Biochemistry for Medics

22. Absorption of amino acids Biochemistry for Medics 22

23. Proteins are completely digested to constituent amino acids. But some amounts of oligopeptides may remain undigested. The products of digestion are rapidly absorbed. Site of Absorption- Oligopeptides are absorbed from duodenum. and proximal Jejunum, while amino acids are absorbed from ileum and distal jejunum . Absorption of amino acids 23 Biochemistry for Medics

24. Mechanism of Absorption- The absorption takes place by active transport (same as that of glucose). Natural L-amino acids are actively transported. D- amino acids are absorbed by simple diffusion. Vitamin B6 is involved in the active transfer of amino acids. Energy requiring process, ATP is required as a source of energy A carrier protein is also required which may be Na+ dependent or independent. Different carrier proteins are there specific for different amino acids. Absorption of amino acids 24 Biochemistry for Medics

25. Absorbed by active transport Intracellular peptidases hydrolyze them to amino acids Hydrolysis is rapid to keep peptide concentration low in the cell Transport mechanism is independent of L- amino acids Absorption of Oligopeptides 25 Biochemistry for Medics

26. Glutathione participates in the Active group translocation of L- amino acids in to the cells of small intestine, kidneys, seminal vesicles, epididymis and brain . A cyclic pathway, operates in which Glutathione is regenerated again, it is named as Gamma Glutamyl Cycle or Meister cycle( Based on the name of Scientist). Role of glutathione 26 Biochemistry for Medics

27. Transamination & Deamination of Amino Acids and urea cycle

28. CONTENT TRANSDEAMINATION TRANSAMINATION DEAMINATION

29. TRANSDEAMINATION The amino group of amino acids is released by a coupled reaction called TRANSDEAMINATION Transamination followed by (Cytoplasm of all body cells) oxidative deamination (Mitochondria of liver cells)

30. Transamination Transamination   is a chemical reaction between two molecules. One is an amino acid, which contains an amine (NH 2 ) group. The other is a  keto acid, which contains a  keto  (=O) group. In transamination, the NH 2  group on one molecule is exchanged with the =O group on the other molecule. The amino acid becomes a keto acid, and the keto acid becomes an amino acid. Transamination in biochemistry is accomplished by enzymes called transaminases or aminotransferases.

31. Reaction

32. 32 General scheme of transamination amino acid 2-oxo acid 2-oxoglutarate glutamate aminotransferase pyridoxal phosphate

33. DEAMINATION Deamination  is the removal of an amine group from a molecule.  Enzymes  which  catalyze  this reaction are called  deaminases . In the human body, deamination takes place primarily in the liver, however glutamate is also deaminated in the kidneys. Deamination is the process by which amino acids are broken down if there is an excess of protein intake. The amino group is removed from the amino acid and converted to ammonia.

34. Deamination of amino acids Deamination - elimination of amino group from amino acid with ammonia formation. Four types of deamination: - oxidative (the most important for higher animals), - reduction, - hydrolytic, and - intramolecular

35. Reduction deamination: R-CH(NH 2 )-COOH + 2H +  R-CH 2 -COOH + NH 3 amino acid fatty acid Hydrolytic deamination: R- CH(NH 2 )-COOH + H 2 O  R- CH( OH )-COOH + NH 3 amino acid hydroxyacid Intramolecular deamination: R- CH(NH 2 )-COOH  R- CH -CH -COOH + NH 3 amino acid unsaturated fatty acid

36. Oxidative deamination During  oxidative deamination , an amino acid is converted into the corresponding keto acid by the removal of the amine functional group as ammonia. The amine functional group is replaced by the ketone group. The ammonia eventually goes into the urea cycle. Oxidative deamination occurs primarily on glutamic acid because glutamic acid was the end product of many transamination reactions. The glutamate dehydrogenase is controlled by ATP and ADP. ATP acts as an inhibitor whereas ADP is an activator.

37. 37 Proteins NH 3 glutam ate glutam ate + urea (ex c re tion by urine ) 2-oxoglutar ate + glutamin e proteol ysis dehydrogena tion + deamina tion detoxi cation in liver deami d a tion in kidney amino acids transamina tion detoxi cation in other tissues NH 4 + (ex c re tion by urine ) NH 4 + (ex c re tion by urine ) deamina tion in kidney Intake, catabolism, and excretion of nitrogen

38. Introduction of Urea Discovered in 1727 By Dutch scientist Herman Boerhaave In 1828, the German chemist Friedrich Wohler obtained urea artificial By treating silver cyanate with ammonium chloride. AgNCO + NH 4 Cl → (NH 2 ) 2 CO + AgCl

39. Introduction of Urea (cont.…) This was the first time an organic compound was artificially synthesized from inorganic starting materials, without the involvement of living organisms. Wohler said " I must tell you that I can make urea without the use of kidneys, either man or dog. Ammonium cyanate is urea."

40. Introduction of Urea (cont.…) For this discovery, Wohler is considered by many the father of organic chemistry.

41. Urea Cycle

42. Urea Cycle Also known as “ ornithine cycle ” cycle of biochemical reactions occurring in many animals Produces urea ((NH2)2CO) from ammonia (NH3 ). In mammals, the urea cycle takes place primarily in the liver, and to a lesser extent in the kidney.

43. Urea Cycle (cont.…) Urea is synthesized in the liver Than secreted into blood stream And taken up by the kidneys for excretion in the urine. Partly takes place in mitochondria and partly in cytoplasm. End product of protein metabolism.

44. Urea Cycle (cont.…) Ammonia is toxic to body Detoxified and converted into urea in urea cycle. The overall reaction of the urea cycle is as follow: NH 4 + + HCO 3 - + H 2 O + 3ATP + Aspartate Urea + 2ADP + AMP + 2Pi + PPi + Fumarate

45. Thank You