On the Mechanism of the Alterations of Rat Kidney Transamidinase Activities by Diet and Hormones
The first reaction in the biosynthesis of creatine is the transfer of the amidine group of arginine to the amino group of glycine to form ornithine and guanidinoacetic acid. This reaction is catalyzed by the enzyme L-arginine: glycine amidinotransferase, EC 18.104.22.168, commonly called transamidinase. Transamidinase was discovered by Borsook and Dubnoff in 19411 and the only tissues from the rat that have significant transamidinase activities are kidney and pancreas 1–5. The second reaction in the biosynthesis of creatine is the methylation of guanidinoacetic acid in the liver by S-adenosylmethionine catalyzed by the enzyme S-adenosylmethionine: guanidinoacetate N-methyltransferase, EC 22.214.171.124. Hormonal induced alterations in this enzyme activity have not been found6. Livers from rats fed complete diets supplemented with creatine had similar guanidinoacetate methyltransferase activities as from rats fed the complete diet without creatine7. Rat kidney transamidinase activities have been found to be alteréd greatly in a variety of dietary and hormonal states. Thus transamidination is thought to be the control step in creatine biosynthesis. Since ornithine is a product of this enzyme reaction, an interrelationship may exist between the control of creatine and urea synthesis.
KeywordsGrowth Hormone Urea Synthesis Complete Diet Amidine Group Glycine Amidinotransferase
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