Open AccessPhenylalanyl‐tRNA Synthetase from Baker's Yeast
Author(s) -
HAAR Friedrich
Publication year - 1976
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1976.tb10314.x
Subject(s) - aminoacylation , ionic strength , chemistry , steady state (chemistry) , phenylalanine , salt (chemistry) , transfer rna , kinetics , reaction rate constant , ionic bonding , enzyme , stereochemistry , thermodynamics , crystallography , biochemistry , rna , amino acid , ion , organic chemistry , physics , aqueous solution , quantum mechanics , gene
Steady‐state kinetic data of aminoacylation of tRNA Phe by phenylalanyl‐tRNA synthetase depend an salt concentration. At 5 mM KCI and 20 mM MgSO 4 a non‐linear curve is found in the double‐reciprocal plot for ATP and phenylalanine, while at 200 mM KCI and 50 mM MgSO 4 a linear curve is observed. KCl and MgSO4 dependence of the reaction also show biphasic curves with intersection points of the two extrapolated linear parts at 50 mM and 10 mM, respectively. A hiphasic curve is also found if the concentration of CTP is varied at constant low ATP concentration. Extrapolations of the linear parts of the curves for ATP as well as for CTP at 5 mM KCl and 20 mM MgSO 4 intersected the 1/[NTP] axis at 1.2 ± 0.1 mM. Hence the existence of a non‐linear curve for ATP as well as phenylalanine does not necessarily indicate two non‐equivalent binding sites for these substrates. A more likely explanation is the existence of two different molecular forms of phenylalanyl‐tRNA synthetase which are interconvertible by salz. This explanation is substantiated by the observation that proteolytic digestion of phenylalanyl‐tRNA synthetase is more easily achieved at low than at medium ionic strength. In addition mischarging of tRNA IIc with phenylalanine by phenylalanyl‐tRNA synthetase occurs at a moderate rate at 5 mM KCI and 20 mM MgSO 4 whereas it is largely depressed by addition of either 5 mM CTP or 150 mM KCI.