Protein metabolism and its regulation
Proteins are large macromolecules or biomolecules consisting of one or more long chains of amino acid. Protein metabolism is biochemical processes responsible for the production of proteins/amino acids by anabolism and breakdown of proteins/amino acids by catabolism. Generally Protein synthesis (anabolism) is a process in which protein are made from amino acids. Protein breakdown (catabolism) is a process in which proteins are broken down into amino acids, also called proteolysis. Mainly, this occurs by the hydrolysis of the peptide bond, and is commonly done by cellular enzymes which are called proteases, but also occur through intramolecular digestion, as well as by some non-enzymatic methods, like; bythe action of mineral acids and heat.
Proteolysis have many purposes in organism; e.g., digestive enzymes breakdown proteins in food particles to provide amino acids for the organism, proteolysis processing of polypeptide chains after their synthesis is required for the production of active proteins. It is also important for the regulation of somecellular processes; it also prevents the accumulation of undesired proteins in the cell. Sometime Abnormal proteolysis process is responsible for many diseases. Other diseases due to abnormal proteolysis are muscular dystrophy, respiratory diseases, skin degenerative disorders and malignancy.
The hormones necessary for the metabolism of protein are called growth hormone (STH), insulin, anabolic hormones, glucocorticoids and thyroid hormones.
Insulin stimulates AA uptake into cells, may also regulate translation, and may increase phosphorylation of ribosomal protein The absence of insulin reduces protein synthesis almost to zero because of the lack of the above effects and because the decreased availability of glucose leads to a greater use of AA for energy.
Glucocorticoids decrease the quantity of protein in most tissues, raising the levels of AA in the plasma. Absence of glucocorticoids leads to inadequate availability of AA for either significant gluconeogenesis or ketogenesis from proteins.
Thyroid hormones such as (T4) accelerate cell metabolism generally. If adequate supplies of carbohydrates and lipids are available, along with an excess of AA, thyroid hormones can increase the rate of protein synthesis. When sufficient carbohydrates and lipids are unavailable, T4 leads to rapid degradation of proteins and to the use of the liberated AA for energy.
By M. Wasif Mehmood, Center of Agricultural Biochemistry and Biotechnology (CABB), University of Agriculture Faisalabad.