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DIGESTION AND ABSORPTION OF PROTEINS
V.S.RAVIKIRAN, MSc.
V.S.RAVIKIRAN, MSc., Department of Biochemistry,
ASRAM Medical college, Eluru-534005.AP, [email protected]
om
Action of proteolytic enzymesEnzyme Hydrolysis of bonds formed by
carboxyl groups of
Pepsin Phe, Tyr, Trp, MetTrypsin Arg, LysChymotrypsin Phe, Tyr, Trp, Val, LeuElastase Ala, Gly, SerCarboxypeptidase A C-terminal aromatic amino acids
Caroboxypeptidase B C-terminal basic amino acids
PROTEASES (Peptide hydrolases)Exopeptidases or peptidases Endopeptidases or proteinases Aminopeptidases Dipeptidyl peptidases Serine proteinases (active center has
serine group), e.g. Trypsin Tripeptidyl peptidases Cysteine proteinases (active center
has Cysteine group), e.g. Papain Carboxypeptidases Aspartic proteinases (active center
has Aspartic group), e.g. Pepsin Peptidyl dipeptidases Dipeptidases Tripeptidases Metalloproteinase proteinases
(active center has metal group) Omega peptidases
(A,V,L I,M.F Y)
(K,R, C)
(D,E)
(P,G)
INTESTINE, BRAIN, KIDNEY TUBULES
NEUTRAL AMINO ACID
Clinical applications:
Abnormalities in protein and amino acids digestion and absorption:↓5-oxoprolinase Oxoprolinuria (pyroglutamic aciduria) Partial gastrectomy, pancreatitis, carcinoma of pancreas and cystic fibrosis (CF) Protein losing enteropathy
Defects in intestinal amino acid transport system:
Hartnup’s disease
Imino glycinuria
Cystinuria
Lysinuric protein intoletence
Oasthouse syndrome
Cystinuria:
Intracellular protein degradation:
Cathepsins:
is a Greek word, meaning ‘to digest’ present in phagolysosomes are 18 in numbers; designated as A-T most of them are active around pH 5 Cathepsin N – collagenolytic cathepsin Cathepsin R: degradation of ribosomes Cathepsin B: seen extracellularly in pathological conditions
Ubiquitin pathway:
a 76-residue monomeric protein seen in all cells abundantly is tag for protein degradation and needs ATP and three enzymes Ubiquitin attached proteins are immediately broken down in proteasomes.
Proteosomes:
proteasome assembly has a molecular weight of 2000 kD with 28 subunits and has a central cylindrical hollow core.
Ubiquitin tagged proteins are taken into this barrel, and surrounding proteolytic enzymes digest the protein into small oligopeptides (5-6 aa).
Proteosome degradation is also ATP dependent.
Inter-organ Transport of Amino Acids
• Post absorptive (fasting) • After food
Alanine
GlutamineValine
Alanine
Glutamine
Alanine
Valine
Brain
Kidney
Muscle Liver
Gut
THE END
THANKS FOR YOUR ATTENTION