Striking differences of physical properties for two different phenylalanyl-tRNA synthetases in Cyanophora paradoxa

Abstract

Extracts of Cyanophora paradoxa contain 2 activities for phenylalanyl‐tRNA synthetase (PRS), when assayed with yeast and eubacterial tRNA as substrate. These enzymes can be separated by salting‐out chromatography. Subsequent gel filtration revealed a striking difference in Mr between the 2 enzymes. Whereas the Mr of the enzyme aminoacylating yeast tRNA is 260 000, typical for PRS from lower eukaryotic organisms, the second enzyme has a unique Mr of 80 000. It aminoacylates eubacterial tRNA, but shows no immunological relationship to the corresponding enzyme from Escherichia coli.