The uptake in vitro of C14-labeled glycine, l-leucine, and l-lysine by different components of guinea pig liver homogenate.

We have reported (1) that n-lysine labeled with Cl4 can be incorporated into the proteins of guinea pig liver homogenate under two different conditions. In the one case the enzyme used was the whole homogenate, the optimum pH was near 6.2, there was an obligatory requirement of calcium, and the incorporation was independent of oxygen. This set of conditions is designated below as the “acid calcium” condition. In the other case the enzyme system was the precipitate obtained by centrifuging the homogenate diluted 15-fold with Ringer’s solution at 2500 X g, the optimum pH was near to 7.3, the reaction was accelerated a little by calcium but the presence of calcium was not obligatory, and the incorporation was a little less under nitrogen than under oxygen. This set of conditions is designated below as the “alkaline” condition. We have carried the study further. The homogenate was separated into four fractions by differential centrifugation, which are designated below as Sediments I, II, and III, and supernatant, and we investigated the ability of each of these fractions to incorporate lysine into the proteins under the two sets of conditions. It was found that all three sedimented fractions incorporated lysine into the proteins under the “alkaline” condition, and that the incorporation under the “acid calcium” condition was confined to the supernatant fraction. We have investigated also and report here the incorporation of C14labeled glycine and leucine into the proteins by the three sedimented fractions, the absence of interaction of amino acids on their individual uptake, and the effects of certain metal ions.