Amino Acid Incorporation and Aminoacyl Transfer in a Wheat Embryo System

Abstract

Abstract An amino acid-incorporating system has been obtained from ungerminated wheat embryos. This system has very low endogenous activity, but phenylalanine incorporation can be stimulated by the addition of polyuridylic acid. The poly U-stimulated system is similar to those from other sources in that it requires ribosomal particles, supernatant fluid, soluble ribonucleic acid, adenosine triphosphate, guanosine triphosphate, a nucleoside triphosphate-regenerating system, and magnesium and potassium ions for maximal activity. Puromycin and ribonuclease cause considerable inhibition of phenylalanine incorporation while chloramphenicol has little effect. The polymerization of phenylalanine from phenylalanyl-soluble ribonucleic acid in the presence of polyuridylic acid requires ribosomes, Mg++, K+, GTP, its generating system, and a factor present in the supernatant fraction. This aminoacyl transfer factor from wheat embryos has been partially purified by ammonium sulfate precipitation and DEAE-cellulose column chromatography. The specificity of the ribosomes for the supernatant factor in the transfer reaction was studied with ribosomes from Escherichia coli, guinea pig liver, wheat embryo, and tobacco leaf chloroplasts. The mammalian and wheat ribosomes could interchange their supernatant factors to give aminoacyl transfer but were not active with the E. coli factor. E. coli ribosomes could use only the homologous supernatant fraction. The tobacco leaf chloroplast ribosomes were tested with the wheat supernatant fluid and were found to be active.