Demonstration of two tyrosyl-tRNA synthetases of pea roots

Abstract

Tyrosyl-tRNA synthetase ( l-tyrosine: tRNA ligase (AMP), EC 6.1.1.1) from pea roots was fractionated into two activity regions by DEAE-cellulose chromatography. The two fractions also eluted from a Sephadex G-200 column at different positions. The two synthetase activities from the Sephadex G-200 fractionation rechromatographed on a second DEAE-cellulose column in the same respective positions as on the first DEAE-cellulose column. The synthetase which eluted first from the DEAE-cellulose column (T 1 synthetase) was much less stable than the synthetase which eluted later (T 2 synthetase). Both enzymes had similar pH, ATP and MgCl 2 optima. The two enzymes acylated tyrosyl-tRNA from various plant tissues and calf liver but did not significantly acylate Escherichia coli tRNA. T 1 and T 2 synthetase catalyzed the acylation of the two major isoaccepting tyrosyl-tRNA species of pea. A third tyrosyl-tRNA of pea was acylated by either T 1 or T 2 synthetase at only a very low rate relative to the rate of the crude (ammonium sulfate) synthetase preparation.