PARTIAL REACTIONS OF AMINOACYL TRANSFER RNA-SYNTHETASES AS FUNCTIONS OF PH

  • 1 January 1978
    • journal article
    • research article
    • Vol. 253  (22) , 8061-8064
Abstract
The effect of pH on the properties of the partial reactions of arginyl-tRNA synthetase of Escherichia coli was investigated. Vmax of pyrophosphorolysis of arginyl adenylate has a pH optimum at pH 6.1, but Vmax of the transfer of arginine to tRNA has a pH optimum of 8.2. These values correlate with the pH optima of the ATP:PPi exchange and the overall esterification reaction, respectively. Only the pyrophosphorolysis reaction requires a divalent cation; transfer proceeds in the presence of EDTA. Inorganic pyrophosphate inhibits the transfer reaction to an extent independent of the concentration of tRNA; the maximum inhibition is a function of pH, corresponding to the relative rate of pyrophosphorolysis of the common intermediate compared with the rate of transfer. Apparently, different groups on the enzyme participate in the ratelimiting steps of the 2 partial reactions and these partial reactions have properties consistent with their participation in the overall esterification of arginine with tRNA.

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