In this article we will discuss about:- 1. Features of Protein Metabolism 2. Role of Endocrines in Protein Metabolism 3. Role of Vitamins.
Features of Protein Metabolism:
Proteins are essential constituents of all living cells. Metabolism of protein shows a number of special features.
i. The power of protein synthesis of the human body is very limited.
ii. Storage of protein can only occur under certain specific conditions.
iii. Distribution of protein in the body is also characteristic.
iv. The method of utilisation of amino acids is also peculiar.
v. The end products of protein metabolism are also characteristic. Two other peculiarities are also noticed in connection with protein metabolism.
vi. Nitrogen equilibrium.
vii. Specific dynamic action (S.D.A.). Each one of these characteristics has been described in proper places.
viii. Each animal species and type of tissue is made up of characteristic protein and variations in the animal species and tissue type are mainly due to variation of the protein types in them.
Role of Endocrines in Protein Metabolism:
i. Anterior Pituitary:
Growth or somatotrophic hormone (STH) is found to be protein anabolic, provided the insulin level is high. There is marked increase in the plasma glutamine as well as increased uptake of N2 by the tissues when growth hormone is introduced.
Insulin prevents neoglucogenesis. It stimulates protein synthesis and growth. Insulin and growth hormone of the anterior pituitary operate in close co-ordination since in the absence of either of the two, protein synthesis is retarded.
iii. Adrenal Cortex:
Adrenal glucocorticoids are protein catabolic. Excess of this hormone causes retardation of growth, negative nitrogen balance, etc., due to increased neoglucogenesis.
Thyroxine stimulates protein synthesis. Excessive secretion of thyroxine promotes protein catabolism, wasting of the muscles etc.
Role of Vitamins in Protein Metabolism:
i. Thiamine (Vitamin B1):
Thiamine helps the enzyme system which is responsible for the synthesis of fats from proteins.
ii. Pyridoxine (Vitamin B6):
This vitamin takes part in the normal tryptophan metabolism, being a constituent of the enzyme kynureninase, responsible for conversion of kynurenine to anthranilic acid and 3-hydroxy-kynurenine to 3-hydroxyanthranilic acid. Pyridoxine acts as a prosthetic group for the enzyme transaminase and as a coenzyme for those enzymes which decarboxylate tyrosine, arginine, glutamic acid and 3, 4-dihydroxy phenylalanine (DOPA).
iii. Cyanocobalamin (Vitamin B12):
This plays an important role in the synthesis of nucleic acid. Deficiency of it causes a disturbance of the DNA metabolism. This vitamin helps in connection with the formation of methyl groups and in the reactions of transmethylation as in the biosynthesis of methionine. It acts as coenzyme and has been found to catalise the enzymatic conversion of glutamate to p-methyl aspartate in bacterial system and to catalise the isomerase reaction in animal tissues where methylmalonyl CoA is converted to succinyl CoA.
iv. Biotin (Vitamin H):
Biotin is linked up with riboflavin. It acts as a coenzyme and helps in decarboxylation. It also helps in the deamination of threonine, serine and aspartic acid.
v. Ascorbic Acid (Vitamin C):
This vitamin helps in the development of protein matrix in the bones. Ascorbic acid takes part in the oxidation of p-hydroxyphenyl pyruvic acid to homogentisic acid which is the intermediate metabolic end product of tyrosine metabolism.
vi. Folic Acid:
It is related with nucleoprotein metabolism. The reduced form of folic acid known as tetrahydrofolic acid acts as a coenzyme in the transfer of formyl and hydroxymethyl group in the biosynthesis of purines.
Riboflavin is a constituent of FMN and FAD which act as coenzymes in enzyme system, e.g., L-amino acid oxidase, xanthine oxidase, and thus related to protein metabolism.