Isolation of a multifunctional protein with aminoimidazole ribonucleotide synthetase, glycinamide ribonucleotide synthetase and glycinamide ribonucleotide transformylase activities: characterization of the aminoimidazole ribonucleotide synthetase

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Abstract
5-Aminoimidazole ribonucleotide (AIR) synthetase, glycinamide ribonucleotide (GAR) synthetase, and GAR transformylase activities from chicken liver exist on a single polypeptide of Mr 110 000 [Daubner, C.S., Schrimsher, J.L., Schendel, F.J., Young, M., Henikoff, S., Patternson, D., Stubbe, J., and Benkovic, S. J. (1985) Biochemistry 24, 7059-7062]. Details of copurification of these three activities through four chromatographic steps are reported. The ratios of these activities remain constant throughout the purification. AIR synthetase has an absolute requirement for K+ for activity and under these conditions has apparent molecular weights of 330 000, determined by Sephadex G-200 chromatography, and 133000, determined by sucrose density gradient ultracentrifugation. Incubation of 18O-labeled formylglycinamidine ribonucleotide (FGAM) with AIR synthetase results in stoichiometric production of AIR, ADP, and [18O]Pi. NMR spectra of .beta.-FGAM and .beta.-AIR are reported.