Participation of Aminoacyl Transfer Ribonucleic Acid in Aminoacyl Phosphatidylglycerol Synthesis

Abstract

Abstract A particulate enzyme from Clostridium welchii catalyzes the synthesis of alanyl phosphatidylglycerol from alanyl-transfer RNA and phosphatidylglycerol. In order to investigate the specificity of alanyl phosphatidylglycerol synthetase toward alanyl-tRNA, a variety of derivatives of alanyl-tRNA have been prepared. N-Acetylalanyl-tRNA and lactyl-tRNA were found to be unsuitable substrates for alanyl phosphatidylglycerol synthesis. Inasmuch as control experiments indicated that the inactivity of these potential substrates could not be ascribed to modifications of the polyribonucleotide chain of the tRNA during the preparation of these derivatives, it was concluded that the synthetase has a recognition site for the aminoacyl group of alanyl-tRNA. In order to determine whether the enzyme also manifests specificity toward the polyribonucleotide chain, alanyl-tRNAcys was prepared and tested as a substrate for alanyl phosphatidylglycerol synthetase. The finding that this compound was inactive as substrate in aminoacyl lipid synthesis, despite the fact that it was active in a poly UG-dependent polypeptide-synthesizing system, indicated that alanyl phosphatidylglycerol synthetase also has a recognition site for at least a portion of the polyribonucleotide chain of alanyl-tRNA. Further support for this conclusion was obtained by experiments with a large molecular weight fragment of alanyl-tRNA produced by limited digestion with T1 RNase. The fragment was found to be inactive as a substrate in alanyl phosphatidylglycerol synthesis.