ABSTRACT
Maximum performance of any organism, by nearly all measures, depends on the efficient utilization of amino acids. Regardless of the final fate of an amino acid, an organism must have the ability to absorb and, in higher organisms, extract from plasma the amino acids essential for life. Knowledge concerning the utilization of lysine is of particular importance because it is the first limiting amino acid in diets of many species. Swine and poultry diets are routinely supplemented with synthetic lysine or are formulated to meet respective lysine requirements. Much of the research concerning tryptophan has centered around the utilization of the unnatural isomer of the amino acid. Arginine metabolism by the domestic cat and other strict carnivores is peculiar in that arginine is utilized for protein synthesis and is of utmost importance in the function of the urea cycle. Teleologically, the cat is rarely without a source of arginine from the high-protein diet it consumes.
