The influence of dietary sulfur upon polyamine biosynthesis in the rat

Thirty female and male Sprague-Dawley rats (175-200g) were randomly divided into six dietary groups of five animals per group and fed diets containing 15% of casein supplemented with cysteine (0.505%) or methionine (0.620%) and varying in the level of inorganic sulfate (0.0002, 0.02 and 0.42%) for a period of 17 days. The polyamines (putrescine, spermine and spermidine) and the enzymes con trolling their biosyntheses were determined in tissue homogenates from the animals in each dietary group.

Rats fed the optimal level of inorganic sulfate (0.02% and supplemented with cysteine had increased L-ornithine decarboxylase (00) activity in liver, kidney, and brain tissues and a decreased S-adenosyl-L-methionine decarboxylase (SAMD) activity in liver and brain tissues from male rats. Spermidine and spermine concentra tions increased in the liver tissues of male rats fed the diet supple mented with cysteine.

S-adenosyl-L-methionine concentrations in the livers of cysteine supplemented animals fed the diets containing 0.02% of sulfate increased. But a decreased incorporation of ¹⁴C-radioactivity from (methyr ^-14 C) methionine into liver tRNA from female animals was observed.

The effect of dietary inorganic sulfate on ODC activity was in conclusive with either cysteine or methionine supplementation. Decreased or increased dietary inorganic sulfate increased S-adenosyl-Lmethionine decarboxylase activity in liver, kidney, and brain tissue from male rats fed diets supplemented with methionine when compared to V vi those fed diets supplemented with methionine and containing the optimal (0.02%) level of inorganic sulfate. In a similar manner decreased or increased levels of inorganic sulfate increased spermine or spermidine concentrations in the liver of male animals fed diets supplemented with methionine. In male animals fed diets supplemented with cysteine, increasing inorganic sulfate levels increased incorporation of the methyl group from methyl ¹⁴ C-methionine into tRNA. Animals fed methionine supplemented diets had an increase in liver S-adenosyl methionine as dietary sulfate was increased.