Zinc(II)-dependent synthesis of diadenosine 5',5'''-P1,P4-tetraphosphate by Escherichia coli and yeast phenylalanyl-tRNA synthetases

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Abstract
A new activity of E. coli and yeast phenylalanyl-tRNA synthetases, the conversion of ATP into diadenosine 5'',5"''-P1,P4-tetraphosphate, is reported. This activity is followed by 31P NMR and chromatography on poly(ethylenimine)-cellulose. It is revealed by the addition of ZnCl2 to a reaction mixture containing the enzyme, ATP-Mg2+, L-phenylalanine and pyrophosphatase. It reflects the reaction of enzyme-bound phenylalanyl adenylate with ATP instead of PPi and strongly depends on the hydrolysis of PPi in the assay medium. The Zn dependence of this reaction parallels that of the inhibition of tRNAPhe aminoacylation which is described in the accompanying paper (Mayaux, J. F., and Blanquet, S., 1981]. In the presence of an unlimiting pyrophosphatase activity, diadenosine tetraphosphate synthesis by E. coli and yeast phenylalanyl-tRNA synthetases occurs at maximal rates of 0.5 and 2 s-, respectively (37.degree. C, pH 7.8, 150 mM KCl, 5 mM ATP, 10 mM, MgCl2, 2 mM L-phenylalanine and 80 .mu.M ZnCl2). Under identical experimental conditions, E. coli isoleucyl-, methionyl- and tyrosyl-tRNA synthetases produce small amounts of diadenosine tetraphosphate at rates 2 or 3 orders of magnitude lower than that achieved by phenylalanyl-tRNA synthetase. In the case of E. coli phenylalanyl-tRNA synthetase, the diadenosine tetraphosphate synthetase activity is accompanied by a diadenosine tetraphosphatase activity. This activity, actually supported by phenylalanyl-tRNA synthetase, is responsible for the appearance of ADP in the assay medium. It requires also the presence of both ZnCl2 and L-phenylalanine. The formation of ADP from diadenosine tetraphosphate and its reaction with enzyme-bound aminoacyl adenylate account for the appearance in the reaction mixture of diadenosine 5'',5"''-P1,P3-triphosphate, after that of diadenosine tetraphosphate. The role of diadenosine tetraphosphate in controlling cellular growth is discussed.

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