Carbocyclic glycinamide ribonucleotide is a substrate for glycinamide ribonucleotide transformylase

The carbocyclic analog of glycinamide ribonucleotide has been synthesized from the racemic parent trihydroxy cyclopentyl amine (B.L. Kam and N.J. Oppenheimer (1981) J. Org. Chem. 46, 3268-3272). This analog was accepted as a substrate (Km = 18 microM, Vmax = 0.23 mM/min) by mammalian glycinamide ribonucleotide transformylase (EC 2.1.2.2) with an efficiency comparable to that of the natural substrate glycinamide ribonucleotide (Km = 10 microM, Vmax = 0.27 mM/min). For each molecule of 10-formyl-5,8-dideazafolate cosubstrate consumed, 0.92 molecule of N-formyl carbocyclic glycinamide ribonucleotide was produced in the enzymatic reaction, indicating a 1:1 stoichiometry. These studies afford the first alternate nucleotide substrate for glycinamide ribonucleotide transformylase and suggest that the ribose ring oxygen of glycinamide ribonucleotide is not critical for enzyme recognition and binding.