Bloehtmtca et Btophyswa Acta, 370 (1974) 585-591 © Elsevier Scientific Pubhsl'ung Company, Amsterdam - - Pnnted in The Netherlands BBA 67351 GMP SYNTHETASE FROM ESCHERICHIA COLI B-96 INTERACTIONS WITH SUBSTRATE ANALOGS THOMAS SPECTOR, RICHARD L MILLER, JAMES A FYFE and THOMAS A NITSKY Wellcome Research Laboratortes, Research Tr:angle Park, N C 27709 ( U S A ) (Received June 17th, 1974) KRE- SUMMARY GMP synthetase was studied with respect to its substrate and Inhibitor speci- fioty towards nine xanthoslne 5'-phosphate (XMP) and GMP analogs 8-AzaXMP and 6-thioXMP were found to be substrates, but were considerably less efficient than XMP 1-Rlbosyloxlpurlnol Y-phosphate was amlnated with an efficiency of less than |/18 000 that of XMP The aminated products of the reactions were competitive lnhibltors, with respect to XMP INTRODUCTION The only known biosynthetic pathway for the formation of guanine occurs at the monophosphate ribonucleotlde level via the amlnatlon of xanthosine 5'-phosphate (XMP) In view of this, the potential amlnatlon of various metabolically produced XMP analogs (see Fig l for basic ring structures) to form GMP analogs could be an important reaction The enzyme that catalyzes this reaction, GMP synthetase, (xan- thoslne Y-phosphate ammoma llgase (AMP), EC 6 3 4 1), has been purified from calf thymus [1], pigeon hver [2], and bacteria [3, 4] The Eschertchla coh enzyme can be derepressed [5] and purified to apparent homogenlty [4] Studies concerning its physical properties [4] catalytic intermediate [6], and the nature of its inhibition by pslcofuranme and decoyenlne [5-9] have been reported However, with the exception of a footnote referring to the substrate properties of dXMP [10], no information has been available concerning the interactions of XMP analogs with this enzyme In the present study, a number of XMP analogs and their corresponding GMP analogs were synthesized, a sensitive substrate activity assay was developed, and the Interactions of these ribonucleotides with GMP synthetase were investigated Abbreviations XMP, xanthosme 5'-phosphate, 1-Oxl-5"-P(l-nbosyloxtpurmol5'-phosphate), 1-rlbosyl-4,6-dlhydroxypyrazolo[3,4-d]-pynmldme 5'-phosphate. 7-Oxl-5"-P (7-nbosyloxlpurmol 5'-phosphate), 7-rlbosyl-4,6-dlhydroxypyrazolo[3,4-d]pyrxmldme 5'-phosphate, 6-NH2-1-Alo-5'-P (6-NH2-1-rlbosylallopunnol 5'-phosphate), 1-rlbosyl-4-hydroxy-6-amlnopyrazolo[3,4-d]pyrlmldme 5'-phosphate, 3-XMP 3-rlbosylxanthoslne 5'-phosphate