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The Mechanism of Action of Methionyl‐tRNA Synthetase

1973; Wiley; Volume: 36; Issue: 1 Linguagem: Inglês

10.1111/j.1432-1033.1973.tb02905.x

1432-1033

Françoise Lawrence, Sylvain Blanquet, Maryse Poiret, Malka Robert-Géro, Jean‐Pierre Waller,

DNA and Nucleic Acid Chemistry

The catalytic properties of native and trypsin‐modified methionyl‐tRNA synthetases were compared in the ATP‐PP i exchange reaction and in the reaction leading to aminoacyl‐tRNA formation performed under comparable experimental conditions. In the ATP‐PP i exchange reaction, the two forms of the enzyme are virtually indistinguishable with respect to ionic requirements and Michaelis constants for ATP and methionine, while V values are in a ratio of 2 to 1 in favor of the native enzyme. In the reaction leading to aminoacylation of tRNA f Met and tRNA m Met , the native and trypsin‐modified enzymes differ in several respects. In particular, a pronounced inhibition by ATP occurs with the native enzyme but not with the trypsin‐modified form. Also, the ratio of the V values measured under optimal conditions are closer to 4 than to 2, in favor of the native enzyme. The ionic requirements for the aminoacylation reaction were examined in detail. Spermine, spermidine and NH 4 Cl, but not KCl, are able to sustain the formation of methionyl‐tRNA in the absence of magnesium, albeit at lower rates than in its presence. A pronounced synergistic effect of MgCl 2 on the reaction catalyzed in the presence of spermidine or NH 4 Cl is described.