Recent experiments have shown that Arg, Lys, and Leu can be incorporated posttranslationally into proteins of regenerating sciatic nerves of rats. The present experiments investigate a mixture of 15 radioactive amino acids to determine if additional amino acids can be conjugated posttranslationally to proteins of regenerating nerves. Proteins of regenerating sciatic nerves of rats were able to incorporate Arg, Lys, Leu, Pro, Val, Ala, Phe, and Ser in relatively large amounts and Asp, Glu, Thr, Gly, Ile, His, and Tyr in relatively low or undetectable amounts, in the most advanced portion of the regenerating nerves. Two-dimensional SDS PAGE showed incorporation of the amino acid mixture into distinct radioactive peaks with molecular weights in the 80-90 kD, 53-66 kD, 22-46 kD, and 17 kD ranges with isoelectric points between 5.0 and 7.9. Most of the amino acids were incorporated into proteins in all of the molecular weight ranges. But Ser was incorporated in highest amounts in the 17 kD range, and Val was most abundant in the 2 2 4 6 kD range. In some cases results indicated that single proteins were modified by several amino acids.
While we do not yet know which amino acids modify specific nerve proteins or the function of the modifications in nerve regeneration, these studies demonstrate the participation of some but not all amino acids in posttranslational modification reactions and the selective modification of specific groups of nerve proteins by these amino acids.