Influence of individual amino acids on uptake and incorporation of valine, glutamic acid and arginine by unfertilized and fertilized sea urchin eggs.

Abstract

1. Tests were made of the uptake and incorporation into protein of a neutral (C14-valine), an acidic (C14-glutamic acid) and a basic(C14-arginine) amino acid in the presence of a mixture of other amino acids and in the presence of a great excess (3000-fold) of each of the other "coded" amino acids by unfertilized and fertilized eggs of Lytechinus pictus. 2. The results showed competition occurring principally among amino acids belonging to the same group. For C14-valine the amino acids that effected strong inhibition (90% or greater) of uptake with unfertilized eggs were ALA, CYS, THR, TYR, HIS, ILU, LEU, MET, PHE and TRY, and with fertilized eggs were CYS, HIS, ILU, LEU, MET and PHE. For C14-glutamic acid 90% inhibition of uptake was given by ASN and ASP with unfertilized eggs and by CYS and GLN with fertilized eggs. Finally, strong inhibition of C14-arginine uptake was demonstrated by LYS and LEU with both unfertilized and fertilized eggs. Similar results were obtained in the corresponding tests of incorporation into protein. The inhibitory effects on incorporation are, then, attributable to competition for uptake. 3. In contrast to the relatively low capability of the unfertilized egg to incorporate amino acid into protein it possesses a relatively high ability to accumulate amino acids from the surroundings. For C14-valine and C14-arginine, the uptake rate by the unfertilized egg was approximately half of that of the fertilized egg, while for C14-glutamic acid the pre- and post-fertilization rates of uptake were approximately the same. 4. The percentage of accumulated C14-amino acid that was incorporated in one hour into protein in these experiments with valine, glutamic acid and arginine was 5, 3 and 0.5, respectively, in the unfertilized eggs and 60, 30 and 6, respectively, in the fertilized eggs. When expressed in terms of uptake, and assuming no large change in the pool of free amino acid in the egg, there is an approximately 10-fold increase in incorporation into protein upon fertilization for each of these three amino acids. 5. The results, also, enable formulations to be made of the kinds of combinations of labeled amino acids that would be the more highly effective in labeling nascent proteins of sea urchin eggs. One such combination would be ILU, ARG, GLU and PRO with each of these being replaceable by certain alternative "competing" amino acids as indicated in the text.