For Medical And Non medical students

1. Digestion & Absorption
of Protein
By
N.Santhosh Kumar
Asst.Professor
Department of Biochemistry
SIMS & RH

2. There is no digestion of
proteins in mouth
Digestion in mouth

3.  When protein enters the stomach, it
stimulates the secretion of the gastrin
hormone from gastric mucosal cells
 Gastrin stimulates the release of
 Gastric juice containing HCl
 proenzyme pepsinogens and rennin
(in infants).
Digestion in stomach

4. HCl
• Secreted by parietal cells
•Unfolds the proteins (denaturized protein)
•Activates the proteolytic enzymes (pepsin)
Pepsin
 Secreted as inactive pepsinogens by chief cells.
Later converted to pepsin by HCl
Pepsinogens
Pepsin
Peptide bonds of aromatic &
acidic a.a’s of proteins
HCl Pepsin
Smaller Peptides + free a.a’s

5. Rennin (Chymosin)
Present in infants (absent in adults)
Action: To clot milk
Required to convert milk into more
solid form
 To prevents rapid passage of milk
from the stomach of infants
Casein
Paracasein
Rennin
Ca- Paracaseinate curd
Ca2+
Further hydrolysis
Pepsin
Renin: secreted by kidney & involves water and electrolyte balance
Coagulates

6. Digestion In The
Intestine
By
Pancreatic Enzymes

7. • Low pH triggers the secretion of the hormones secretin
& cholecystokinin
• Secretin stimulates the release of HCO3 and pancreatic
juice from pancreas into the small intestine
• HCO3 neutralizes the contents from the stomach entered
• Cholecystokinin stimulates the secretion of pancreatic
(peptidase)enzymes

8. Peptidase enzyme secreted by Pancreas
Endopeptidase Exopeptidase
Cleave internal peptide
bonds
Results into smaller peptides
Eg: trypsin, chymotrypsin &
elastase
Hydrolyze the peptide bonds
of terminal a.a’s
Eg: Carboxypeptidase
Amino peptidase

9. Action of Pancreatic
proenzymes

10. (Secreted by duodenal
epithelial cells)
Hydrolyzes small
non polar a.a’s like
Ala, Ser & Gly
Carboxyl group
of aromatic a.a’s
& Splits peptide
linkages of Leu,
Met, Asn & His
Removes the
carboxyl terminal
a.a’s from
peptides
Enterokinase

11. Digestion In Intestine By Small Intestinal Proteases
Amino-peptidase Di-peptidase
Hydrolyze peptide bonds
next to N-terminal a.a’s of
short peptides
Complete digestion of
dipeptides to free amino
acids
Cobalt or Manganese

12. Secretin
Cholecystokinin
Enteropeptidase
Trypsinogen
Gastrin

13. Absorption of amino acids

14. • Involves an active transport
mechanism.
• Required ATP and specific
transport proteins in the
intestinal mucosal cells
• A.a’s released by digestion
pass from the gut through
hepatic portal vein (by
facilitated transporter) to
the liver
• A.a’s are utilized for the
synthesis of proteins

15. • Meister proposed γ-gluyamyl cycle, that glutathione participates
in absorption of a.a’s in intestine, kidneys & brain.
Gamma glutamyl cycle (Meisters cycle)

16. Thank You