Studies on the metabolism of dimethylarginines in rats

点击翻译按钮获取中文摘要

N^G,N^G - and N^G,N'^G -Dimethylarginine (DMA and DM'A) occur in natural proteins methylated post-translationally. Some investigators proposed to use these amino acids as an index of protein turnover in a similar manner to N^<<tau>> methylhistidine, without detailed metabolic studies. By our experiments, however, it was proved that these dimethylarginines were definitely metabolized in rats. Both DMA and DM'A were converted to N^<alpha> -acetyl conjugates and to -keto acids by unique aminotransferase catalyzing the transamination between DMA (DM'A) and pyruvate. In addition, the oxidatively decarboxylated products of the -keto acids were also found as the metabolites. Moreover, it was shown that DMA was catabolized to L-citrulline and other amino acids metabolically related to urea cycle. We found a novel enzyme responsible for the metabolic process of DMA, which catalizes the direct conversion of DMA to L-citrulline with hydrolytic liberation of dimethylamine from the methylated guanidino moiety of DMA. These enzymes were purified from rat kidney and were fully characterized as new enzymes.These findings shows that the attempt to use the above-mentioned dimethyl-arginines as an index of in vivo protein breakdown is inadeqate at least in rats.