The influence of cysteine and methionine supplements on polyamine biosynthesis in the rat.

Previous reports from this laboratory have shown that supplementation of diets containing the optimal level (0.02%) of dietary inorganic sulfate (SO4(2-] with cysteine instead of methionine can affect several metabolic pathways. It is possible that these results reflect alterations in the biosynthesis of potent physiological compounds, the polyamines. Adult male albino rats were fed diets containing 15% casein and a constant level of inorganic sulfate (0.02%) supplemented with cysteine (0.505%) or methionine (0.62%). The polyamines (putrescine, spermidine and spermine) and the controlling enzymes for their biosynthesis ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMD) were evaluated in liver, kidney and brain tissue homogenates following a 17-day dietary period. Rats fed the diet supplemented with cysteine had increased ODC activity and decreased SAMD activity when compared to rats fed diets supplemented with methionine. Polyamine concentrations varied in tissues with a trend toward increasing amounts in animals fed the cysteine-supplemented diet. Based on these data, it appears that dietary cysteine stimulates the biosynthesis and increased tissue concentration of polyamines.