192] GTP cyclohydrolase from Escherichia coli

Abstract

Publisher Summary The activity of GTP (guanosine triphosphate) cyclohydrolase is assessed most easily by measurement of the amount of formate released from GTP. A procedure is devised that results in the oxidation, either enzymatically or chemically of formate to carbon dioxide. A second more convenient assay is developed for use with enzyme preparations that is purified free from formic dehydrogenase. The first step in the biosynthetic pathway for the conversion of GTP to the pteridine portion of folic acid is the hydrolytic reaction that results in the elimination of carbon 8 of GTP as formate. The enzyme that catalyzes the reaction is termed as GTP cyclohydrolase. Purified GTP cyclohydrolase catalyzes the conversion of GTP to dihydroneopterin triphosphate. Thus, the enzyme is responsible for the formation of a product by a set of reactions that theoretically should include the following four steps: two hydrolytic reactions, an Amadori rearrangement of the ribose moiety to a 1-deoxy- 2-ketopentose triphosphate unit, and finally ring closure to yield dihydroneopterin triphosphate.