During digestion, proteins are hydrolyzed into amino acids. Amino acids are absorbed by the capillaries of villi and enter the liver via the hepatic portal vein.

2. Protein and amino acids metabolism
Types of amino acids
Digestion of protein
Metabolism fates of amino acids
Hormonal regulataion of protein metabolism


3. Protein and amino acids metabolism
Metabolism of proteins is the metabolism of amino
acids.
Metabolism of amino acids is a part of the
nitrogen metabolism in body.
Nitrogen enters the body in dietary protein.
 Dietary proteins cannot be stored as such but used for
formation of tissue proteins due to there is a continuous
breakdown of endogenous tissue proteins.
Total chemical reactions taking place in side the body of
organism and it is divided into two types catabolism and
anabolism

4. During digestion, proteins are
hydrolyzed into amino acids. Amino acids
are absorbed by the capillaries of villi and
enter the liver via the hepatic portal vein.

5. Essential amino acids
Lysine, Leucine , Isoleucine, Valine, Methionine, Phenylalanine, Threonine,
Tryptophan
Nonessential amino acids
Alanine, glycine, , aspartate , glutamate, serine, tyrosine, cysteine , proline,
glutamine, aspargine
 For formation of new tissue protein : all essential amino acids
that can not be synthesized by organism & provided by dietary
protein must be present at the same time with nonessential
amino acids that can be synthesized by organism .
Types of amino acids

6. Digestion of protein
Proteins are broken down by hydrolyases
( peptidases or proteases ) :
• Endopeptidases : attack internal bonds and liberate large peptide
fragments ( pepsin trypsin Chmotrypsin & Elastase )
• Exopeptidases : remove one amino acid at a time from -
COOH or -NH2 terminus (amino peptidase &
carboxypeptidase).
 Endopeptidases are important for initial breakdown of long
polypeptides into smaller ones which then attacked by
exopeptidases.
 Digestion of protein can be divided into : a gastric ,
pancreatic and intestinal phases.

7. Pepsinogen Pepsin
HCL
ProteinAmino acid+Oligopeptides & polypeptides

8.  This phase ends with free amino acids and small peptides
of 2-8 amino acid residues which account for 60% of
protein digestion.
• Intestinal enzymes are: aminopeptidases (attack peptide
bond next to amino terminal of polypeptide) & dipeptidase
.
• The end product is free amino acids dipeptides &
tripeptides.

9. Amino acids Construction Synthetic proteins,
hemoglobin, enzymes
Removal amino
Ketone acids + [NH3] Ammonia Urea
Fats
Pyruvate acid
Acetyl - CoA
Glutaric acid
Krebs
cycle

10. Transport and fate of amino acids and protein in liver & muscle
muscle
Alanine plays a special role in transporting
amino groups to liver.
Ala is the carrier of ammonia and of the
carbon skeleton of pyruvate from muscle to
liver.
The ammonia is excreted and the pyruvate is
used to produce glucose, which is returned to
the muscle.
Glutaminase reaction
releases NH3 that
enters the urea cycle in
the liver (in the
kidney, it is excreted
into the urine)

11. Metabolism fates of amino acids
1- Body protein biosynthesis .
2- Small peptide biosynthesis .
3- Synthesis of non-protein nitrogenous (NPN))
compounds (creatine, Urea, ammonia and uric acid
4- Deamination & Transamination to synthesized a
new amino acid or glucose or ketone bodies or
produce energy in starvation.

12. Insulin is the primary anabolic hormone
Glucagon and cortisol are catabolic hormones
Trigger the breakdown of body protein for energy
Hormonal regulatation of protein
metabolism

13. • Alters phosphorylation of many key
intracellular metabolic enzymes (minutes)
• Alters protein synthesis and gene
transcription (hours)

14.  Promotes
• Transport of amino acids
• Protein synthesis
• Gene transcription
 Inhibits protein degradation
 Prevents glucose synthesis in liver
 Preserves amino acids
 Lack of insulin causes elimination of protein stores

15. Prevents hypoglycemia
Increases glucose synthesis from amino
acids
Increases with exercise independent of
blood glucose
Effects of Glucagon

16. Cortisol
Cortisol is produced by adrenal glands
cortisol affects metabolism by
stimulates protein degradation in
muscles while it activates proteins
synthesis in liver tissues

17. Growth hormone is increasing transport of
amino acids to muscle tissues to synthesis
protein
Growth hormone stimulates protein
anabolism in many tissues. This effect
reflects increased amino acid uptake,
increased protein synthesis and decreased
oxidation of proteins
Growth hormone

19. REFERENCES
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translation by insulin. Biochem J. 1997;328:329–41.
 Mendez R, Welsh G, Kleijn M, Myers MG, White MF, Proud CG, Rhoads
RE. Regulation of protein synthesis by insulin through IRS-1. Prog Mol
Subcell Biol. 2001;26:49–93. Medline
 Liu Z, Wu Y, Nicklas EW, Jahn LA, Price WJ, Barrett EJ. Unlike insulin,
amino acids stimulate p70S6K but not GSK-3 or glycogen synthase in
human skeletal muscle. Am J Physiol Endocrinol Metab. 2004;286:E523–
528. Abstract/FREE Full Text
 Fryburg DA, Jahn LA, Hill SA, Oliveras DM, Barrett EJ. Insulin and insulin-
like growth factor-I enhance human skeletal muscle protein anabolism
during hyperaminoacidemia by different mechanisms.