Effect of protein intake and cold exposure on selected liver enzymes associated with amino acid metabolism.

The activity of five liver enzymes involved in amino acid metabolism was found to be markedly increased in coldexposed rats. However, the activity of three of the enzymes, arginase, glutamic-oxalacetic and glutamic-pyruvic transaminase, was increased only as a result of a cold-induced higher protein intake. In contrast, the activity of tryptophan pyrrolase and tyrosine alpha ketoglutaric transminase was increased by cold per se. The data demonstrate that both substrate-induced and cold-induced enzymatic changes occur in cold-exposed animals.