Creatine biosynthesis during embryonic development. False feedback suppression of liver amidinotransferase by N-acetimidoylsarcosine and 1-carboxymethyl-2-iminoimidazolidine (cyclocreatine)

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Abstract
The level of arginine:glycine amidinotransferase in liver of the developing chick embryo is partially suppressed following injection of arginine into the yolk. The level is completely suppressed following injection of guanidinoacetate or creatine. Structural requirements for the physiological suppressor were examined by testing certain analogs of creatine and its biosynthetic precursors for their ability to suppress liver amidinotransferase levels in developing chick embryos and growing chicks. The creatine analogs, N-acetimidoylsarcosine and 1-carboxymethyl-2-iminoimidazolidine (cyclocreatine), suppress liver amidinotransferase levels of both developing embryos and growing chicks. Compounds ineffective as suppressors included: the arginine analog, N5-acetimidoylornithine; the guanidinoacetate analog, N-acetimidoylglycine; and the creatine analog, 1-carboxymethyl-2-iminohexahydropyrimidine. Arginine and guanidinoacetate may need to be converted to creatine before serving as a suppressor. Creatine, not phosphocreatine, seems most closely related to the physiological suppressor of amidinotransferase.