Creatine represents approximately 40 per cent of the total urinary creatinine of young full term infants, but is either absent, or present in small amounts, in the urine of premature infants (l-3). Furthermore, the creotinine coefficients of both premature and full term infants are lower than those of children and adults (4). One possible explanation of these phenomena in the premature infant is a lower functional level of the enzyme systems necessary for the synthesis of creatine. As a step

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... ard the possible elucidation of this question, we have examined preparations of liver from adult and embryonic members of various species with respect to their ability to synthesize creatine from guanidoacetic acid and n-methionine. Borsook and Dubnoff (5, 6) reported that liver slices from the cat, dog, guinea pig, frog, pigeon, rabbit, and rat were able to form creatine from guanidoacetic acid and methionine. Homogenates of the liver of the guinea pig were also able to perform this synthesis in the presence of adenosinetriphosphate (ATP) (7). Rat liver homogenates were much less effective. Sourkes (8) reported that homogenates of beef liver were capable of synthesizing creatine from Dn-methionine and guanidoacetic acid at a rate considerably in excess of that noted by Borsook and Dubnoff in the guinea pig. EXPERIMENTAL Animals-Swine, sheep, and beef livers were obtained from a local slaughter-house. The rats were bred from the Wistar Institute strain; the hamsters and chickens were of the Syrian and Rhode Island red strains, respectively. The guinea pigs and rabbits were obtained commercially. The laboratory animals were fed commercial diets. Methods-The livers from swine, sheep, and beef were stored on ice and