DIGESTION AND ABSORPTION OF PROTEINS

V.S.RAVIKIRAN, MSc.

V.S.RAVIKIRAN, MSc., Department of Biochemistry,

ASRAM Medical college, Eluru-534005.AP, India.vsravikiran2013@gmail.c

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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