Why insulin is key for intracellular protein synthesis
When you’ve just eaten some protein, insulin, glucagon, growth hormone and glucocorticoids increase because of the presence of elevated amino acid concentration (1p232). The insulin promotes the protein synthesis and the other hormones have an opposite effect (1p232). Growth hormone is anabolic like insulin, although counterregulatory (1p232). Insulin to glucagon ratio favoring insulin stimulates protein synthesis enzymes and vice versa (1p232). The insulin is needed for uptake of amino acids across the cell membrane and antagonizing activation of amino acid oxidation by some enzymes (1p206-207).
Protein synthesis is also sensitive to multiple influences including stability of mRNA, amount of rRNA, activity of ribosomes, and (most important from diet), the presence of essential and nonessential amino acids in appropriate concentration to charge the tRNA and hormone environment (1p232). When amino acids are not present or not present in sufficient quantity, amino acid oxidation increases (1p232).
1. Gropper SS, Smith JL, Groff JL. Advanced Nutrition and Human Metabolism. Belmont, CA: Thomson Wadsworth, 2009.