Substrate specificity of formylglycinamidine synthetase.

Formylglycinamidine ribonucleotide (FGAM) synthetase, which catalyzes the conversion of formylglycinamide ribonucleotide (FGAR), glutamine, and ATP to FGAM, ADP, glutamate, and Pi, has been purified to homogeneity (sp act. 0.20 mumol min-1 mg-1) from chicken liver by an alternative procedure to that of Buchanan et al. [Buchanan, J. M., Ohnoki, S., & Hong, B. S. (1978) Methods Enzymol. 51, 193-201] (sp act. 0.12 mumol min-1 mg-1). A variety of new analogues of formylglycinamide ribonucleotide have been prepared in which the formylglycinamide arm (R = CH2NHCHO) has been replaced by R = CH3, CH2OH, CH2Cl, CH2NH3, CH2NHCOCH3, CH2NHCOCH2Cl, CH2NHCO2CH2Ph, and L-CHC-H3NHCHO. These compounds have been characterized by 1H and 13C NMR spectroscopy. With compounds R = CH3, CH2OH, and CH2NHCOCH3 and ATP, in the presence or absence of glutamine, FGAM synthetase catalyzes the production of Pi at 4.5, 48, and 20%, respectively, the rate of production of Pi from formylglycinamide ribonucleotide. Only R = CH2NHCOCH3 causes glutaminase activity as well as ATPase activity and has been shown to be converted to the amidine analogue. Both FGAR (R = CH2NHCHO) and the FGAR analogue (R = CH2NHCHOCH3) in the presence of ATP and FGAM synthetase and in the absence of glutamine form a complex isolable by Sephadex G-50 chromatography. FGAM synthetase is thus highly specific for its formylglycine side chain. [18O]-beta-FGAR was prepared biosynthetically, and FGAM synthetase was shown by 31P NMR spectroscopy to catalyze the transfer of amide 18O to inorganic phosphate.