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J. Biochem, 1968, Vol. 64, No. 2 181-188
© 1968 Japanese Biochemical Society

research-article

Studies on Amino-acyl-tRNA Synthetases from Pseudomonas aeruginosa* II. Properties of Leucyl-, and Tyrosyl-tRNA Synthetases

YOSHITO KAZIRO, YASUSHI TAKAHASHI** and NORIKO INOUE

From the Department of Chemistry, Instituts of Medical Science, University of Tokyo, Takanawa, Minato-ku Tokyo

The properties of leucyl- and tyrosyl-tRNA synthetases [EC 6.1.1.4 [EC] and 6.1.1.1 [EC] ] from Pseudomonas aeruginosa are described. Both enzymes are stable when kept frozen at—20°C in the presence of 25% glycerol. The purified preparation are slightly contaminated with inactive proteins as judged by polyacrylamide gel electrophoresis. The kinetic constants of the two enzymes are determined using ATP{leftrightharpoons}32PP1 exchange assay and 14C-amino-acyl-tRNA synthesis assay. Both enzymes display a rather broad pH optimum ranging from 7.5 to 9.0 in Tris-HG1 buffer.

Leucyl-tRNA synthetase requires the presence of NH4+ ions for its activity. The stimulatory effect of NH4+ ions is found to be on the second step of the leucyl-tRNA synthetase reaction, namely the transfer of the leucyl group from an enzyme-bound leucyl adenylate to tRNA, for the rate of ATP{rightleftharpoons}32PP1 exchange is not affected by NH4+ ions.

Leucyl-, and tyrosyl-tRNA synthetases of P. aeruginosa aminoacylate E. coli tRNA to the same extent as the homologous E. coli enzymes, but do not react with yeast tRNA. Purified leucyl-tRNA synthetase of P. aeruginosa is able to recognize the multiple E. coli tRNA species specific for leucine obtained by fractionation on a DEAE-sephadex column.

*Preceding paper of this series (1).

**On leave od absence from the Nippon Kayaku Co., Ltd. Present address: Ohji Pharmaceutical Works, Nippon Kayaku Co., Ltd., Kita-ku, Tokyo.


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