Protein metabolism refers to all enzymatically catalyzed chemical reacting taking place within an organism or its individual cells involved in growth reproduction, tissue repair and energy production. Metabolic reactions are either synthetic or anabolism or degradation called catabolism. The modes of protein metabolism are as follows.

(1) Deamination:

It takes place in liver and kidney cells. During this process amino group is removed from the a-amino acids to form a a-keto acid. The amino group is converted to urea.

(2) Oxidative deamination:


In this reaction amino group is simply removed from donor amino acids. Through oxidative deamination 50% of common amino acids reduced to these carbon residues and from Acetyl-COA which enters into TCA cycle for yielding energy.

(3) Trans amination:

Transamination is the process which brings about the transfer of aminogroup from donor amino acid to a recipient keto-acid under the influence of transaminase. Thus the donor amino acid becomes keto-acid and keto-acid becomes the amino acid.

(4) Decarboxylation:


It is a process by which COOH group leaves a primary amine as CO and is probably not an important pathway of amino acid metabolism.

(5) Transmethylation:

In this process the methyl group is transferred from one compound to other. These methyl groups may be used in the formation of choline, creatine and other important compounds.

Protein synthesis: This is the formation of polypeptides and protein by addition of amino acids in Ribosome under genetic controls by the coding of nucleic acids.