Age-related changes in transfer RNAs and synthetases in germinating soybean (Glycine max) cotyledons

Transfer RNAs and aminoacyl-tRNA synthetases were isolated from 5- and 20-day-old etiolated ageing soybean cotyledons. The relative concentrations of Mg2+ and ATP for optimal acylation (using homologous tRNAs and synthetases) for the 16 amino acids tested indicate that the amino acids can be grouped into 3 categories with a Mg:ATP ratio of 2:1, 5:1 and 10:1 (aspartic acid, isoleucine, leucine, serine, and valine). The total amino acid acceptance for 5-day-old cotyledons was 0.427 mumol tRNA and 0.349 mumol/mumol tRNA for 20-day-old cotyledons. This shows that as cotyledons age, tRNA preparations show an overall decrease of 16.6% amino acid acceptance ability compared to tRNA from younger cotyledons. Charged tRNA samples from 5- and 20-day cotyledons chromatographed on RPC-5 columns demonstrate pronounced qualitative and quantitative changes in tRNA species as cotyledons age, including displacements of peaks as in alanyl-tRNAs and glycyl-tRNAs; disappearance of some species as in valyl-tRNAs, glutamyl-tRNAs, leucyl-tRNAs, lysyl-tRNAs, arginyl-tRNAs, histidyl-tRNAs and tyrosyl-tRNAs and formation of new species as in phenylalanine-tRNA.