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 L-lysine labeled with C14 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