Enzymes essential for the biosynthesis of nucleic acid guanine; inosine 5'-phosphate dehydrogenase of Aerobacter aerogenes.

Previous studies on purineless mutants of Aerobacter aerogenes have shown that a guanineless mutant, strain P-14, which accumulates xanthosine in its culture fluids, lacks the ability to produce nucleic acid guanine either by synthesis de novo or from adenine, but is capable of synthesizing nucleic acid adenine from small precursors (24). These results appeared to implicate a derivative of xanthosine as an obligatory intermediate in the formation of nucleic acid guanine from a common purine precursor,’ presumably 15’P (2, 5, 6). The present communication describes the isolation and properties of “15’P dehydrogenase,” an enzyme catalyzing the oxidation of 15’P to X5’P, and demonstrates the obligatory role of this enzyme in the synthesis of nucleic acid guanine. A similar oxidation of 15’P to X5’P has recently been observed in rat bone marrow (7) and in pigeon liver (8). The conversion of X5’P to G5’P is treated in the succeeding paper (9).