Download PROTEIN METABOLISM

PROTEIN METABOLISM
DEPT OF BIOCHEMISTRY
ACS MEDICAL COLLEGE
CHENNAI - 77
DIGESTION & ABSORPTION
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 NONNITROGEN CONTAINING METABOLITES
DIGESTION TAKES PLACE WITH
THE HELP OF ENZYMES
SECRETED BY
1. STOMACH
2. PANCREAS
3. SMALL INTESTINE
1.DIGESTION IN STOMACH
ENTERING PROTEINS (+)
GASTRIN (+) GASTRIC JUICE
(pH 1.5 – 2.5) CONTAINING
1. HCL
2. PEPSINOGEN
3. RENNIN (IN INFANTS)
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
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
PEPSINOGEN
PEPSIN
H+(pH 1.5 – 2.5)
PEPSIN
DIETARY PROTEIN
SMALLER PEPTIDES + AA
RENNIN
• CHYMOSIN / RENNET
• IMPORTANT IN INFANTS DIGESTIVE
PROCESS
• CLOTTING OF MILK
CASEIN
R
PARACASEIN
Ca++
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
2.DIGESTION IN INTESTINE
BY PANCREATIC ENZYMES
ACIDIC CONTENTS (CHYME)
PASSING INTO SMALL
INTESTINE TRIGGERS THE
SECRETION OF
1. SECRETIN
2. CHOLECYSTOKININ
SECRETIN
• STIMULATES PANCREAS TO
SECRETE BICARBONATE &
RELEASE OF PANCREATIC
JUICE INTO THE SMALL
INTESTINE.
• NEUTRALISES GASTRIC HCL
CHANGING pH FROM 1.5 – 7.0
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
ACTIVATION OF PANCREATIC
PRO-ENZYMES
TRYPSINOGEN
ENTEROPEPTIDASE
TRYPSIN
CHYMOTRYPSINOGEN
PRO-ELASTASE
PROCARBOXYPEPTIDASE
CHYMOTRYPSIN
ELASTASE
CARBOXYPEPTIDASE
• 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 NONPOLAR AA RESIDUES SUCH AS ALA, SER &
GLY
• THUS 3 ENZYMES HYDROLYSE
POLYPEPTIDES TO SMALLER PEPTIDES
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
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
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
ABSORPTION OF AMINOACIDS
• MOSTLY THRU ACTIVE TRANSPORT
• 5 SEPARATE SYSTEMS – TRANSPORT LAMINOACIDS 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
TRANSPORT
SYSTEM
AMINOACID
TRANSPORTD
DISORDER
Small neutral
aminoacids
Ala Ser & Thr
Large neutral
aminoacids
Basic aa &
Cysteine
Isoleu, Leu,
Val,Tyr,Trp,Ph
e
Arg, Lys,
CYSTINUTIA
Ornithine, Cys
Acidic
aminoacids
Glutamic acid
Aspartic acid
Iminoacid,
Glycine
Pro, Hydroxy
pro, Gly
HARTNUP
Disease
GLYCINURIA
MEISTER CYCLE
GAMMA GLUTAMYL CYCLE
AMINO ACID
GLUTATHIONE
GLUTAMYL AMINOACID
CYSTEINYL GLYCINE
AMINOACID
GLYCINE CYSTEINE
OXOPROLINE
GLUTAMYL-CYSTEINE
GLUTAMATE