Abstract: The influence of pyrophosphate hydrolysis by inorganic pyrophosphatase on homologous aminoacylation of different yeast tRNA(Phe) mutants was studied. The addition of pyrophosphatase significantly improved the aminoacylation efficiency of tRNA(Phe) structural mutants as well as the mutant with substitution at position 20, while having no effect on the charge of wild-type tRNA(Phe). Aminoacylation of tRNA(Phe) anticodon and discriminator base (N(73)) mutants was not affected by pyrophosphatase. Activation of wild-type tRNA(Phe) transcript aminoacylation by inorganic pyrophosphatase was observed only at low Mg(2+) concentrations due to distortion of the tRNA(Phe) structure under these conditions. Our results demonstrate that pyrophosphate dissociation becomes a rate-limiting step of the reaction in yeast phenylalanyl-tRNA synthetase catalyzed aminoacylation of tRNA(Phe) variants with altered tertiary structure. A possible mechanism of pyrophosphate-mediated inhibition of tRNA mutants aminoacylation is discussed.