[Separation and comparative characteristics of subunits of phenylalanyl-tRNA synthetase from Escherichia coli MRE-600 and Thermus thermophilus HB8]

Abstract

Separation of alpha- and beta-subunits of phenylalanyl-tRNA-synthetases from E. coli MRE-600 and Thermus thermophilus HB8 using FPLC has been carried out for the first time. The separated subunits of both enzymes do not possess any detectable tRNA-amino-acylation activity. It was found that in the case of the E. coli enzyme beta-subunits exist in solution mainly in the monomeric form with negligible formation of beta 2-dimers, while alpha-subunits predominantly form alpha 2-dimers over the same concentration range. In the case of Thermus thermophilus phenylalanyl-tRNA-synthetase, both alpha- and beta-subunits mainly exist in the dimeric form. The putative mechanisms of alpha-subunit aggregation and of subunit association for alpha 2 beta 2-type enzymes are discussed.