Synthesis of diadenosine 5',5''' -P1,P4-tetraphosphate by lysyl-tRNA synthetase and a multienzyme complex of aminoacyl-tRNA synthetases from rat liver.

An 18 S multienzyme complex of aminoacyl-tRNA synthetases is found to be active in the synthesis of diadenosine-5',5'''-P1,P4-tetraphosphate (AppppA). Most of the activity is attributed to lysyl-tRNA synthetase in the complex. Free lysyl-tRNA synthetase dissociated from the synthetase complex is about 6-fold more active than the complex in AppppA synthesis, while their apparent Michaelis constants for ATP and lysine are similar. AMP, which reportedly activates AppppA synthesis (Hilderman, R.H. (1983) Biochemistry 22, 4353-4357), has no effect on AppppA synthesis. The higher activity of free Lys-tRNA synthetase is in part due to the higher stimulation of AppppA synthesis by Zn2+. These results suggest that association of aminoacyl-tRNA synthetases may affect AppppA synthesis.