Protection of bovine seryl-transfer ribonucleic acid (seryl-tRNA) synthetase from chemical modification by its substrates, and some kinetic parameters.

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Abstract
Amino acid residues contained in the recognition sites of seryl-transfer ribonucleic acid (tRNA) synthetase (SerRS) were studied by chemical modification. Ser residues were modified with phenylmethanesulfonyl fluoride, and appeared to be unnecessary for the recognition. However, the modification of Arg residues with phenylglyoxal, His residues with diethylpyrocarbonate and sulfhydryl groups with 5,5''-dithiobis(2-nitrobenzoic acid), N-ethylmaleimide, iodoacetic acid or iodoacetamide showed that these residues were essential for the tRNA recognition by SerRs. Protection experiments with substrates from inactivation of Ser-tRNA formation by modification suggested that Arg residues interact with the .gamma.-phosphate of adenosine triphosphate and tRNA. Modification of sulfhydryl groups showed that the groups interact with the hydroxyl groups of ribose of the CCA-end on tRNA. Furthermore, in order to understand the recognition mechanism between SerRS and tRNASer, some kinetic parameters such as the Km and Vmax values of yeast tRNASer and E. coli tRNASer for bovine SerRS were compared with the values of bovine tRNASer.