Some factors affecting kidney transamidinase activity in rats.

Although it is well established that only two enzymes, transamidinase and guanidoacetate methylpherase, are directly involved in the formation of creatine (l-4), almost nothing is known about the regulation of creatine synthesis. Since various diseases alter creatine metabolism (5), it is possible that a study of transamidinase and guanidoacetate methylpherase activities in some of these diseases would furnish clues to the physiological control of creatine synthesis. One of the diseases that disturbs creatine metabolism is hyperthyroidism (6) and it will be shown in the present report that hyperthyroidism reduces kidney transamidinase activity. Since this could be due to the elevated blood creatine concentration of hyperthyroidism (B), creatine feeding experiments were conducted. The data obtained show that excess creatine also reduces the activity of kidney transamidinase in the rat and demonstrate a feedback mechanism (7) in a mammal.