Detection and partial purification of rapidly sedimenting forms of aminoacyl-transfer ribonucleic acid synthetases from human placenta

Abstract

The pattern of aggregation of aminoacyl-tRNA synthetases in extracts of human placenta is described. The sedimentation behavior of aminoacyl-tRNA synthetases in crude extracts of human placenta was analyzed by velocity gradient centrifugation. Varying proportions of seven aminoacyl-tRNA synthetase activities (arginyl-, glutaminyl-, glutamyl-, isoleucyl-, leucyl-, lysyl-, and methionyl-tRNA synthetases) sedimented as broad peaks at 17 to 21 S. Twelve other aminoacyl-tRNA synthetases sedimented at 5 to 9 S, a range more typical of individual aminoacyl-tRNA synthetases. The seven aminoacyl-tRNA synthetases which are aggregated in the placenta are the same enzymes which are most often reported to be aggregated in diverse mammalian species and tissues. All seven of the aggregated activities copurified as 16.2 to 18.8 S forms by ammonium sulfate precipitation, fractionation on alumina C γ and calcium phosphate gels, and chromatography on diethylaminoethyl (DEAE) cellulose. Before their gradient elution from DEAE-cellulose, the aggregated aminoacyl-tRNA synthetases could be stored with little loss of activity or change in sedimentation profile. Gradient elution of the aggregated activities from DEAE-cellulose columns resulted in accelerated loss of the activities during storage and in reduced sedimentation rates. Further reductions in sedimentation coefficients of aminoacyl-tRNA synthetases were observed after storage of fractions recovered from DEAE-cellulose columns.