Isolation and Characterization of a Cyclic Phosphate of Neopterin and Other 6-Alkylpterin Compounds Enzymatically Synthesized from GTP by Cell-free Extracts of Serratia indica

Abstract

A cell-free system for the biosynthesis of L-threo-neopterin, a growth factor for protozoan, Crithidia fasciculata from guanosine-5'-triphosphate (GTP) was obtained from extracts of Serratia indica IFO 3759. This preparation catalyzed the production of a specific pteridine from GTP, which was isolated and characterized as a cyclic phosphate of neopterin (cNP). Among the other products, L-threo-neopterin, as the Crithidia factor, 6-hydroxymethylpterin, and erythro-neopterin were tentatively identified. Requirements for the synthesis of these products include GTP, Mg²⁺, and disodium phosphate. Fluorescence formation was inhibited by purine nucleotides.
When a disodium phosphate was included in the reaction system, cNP and erythro-neopterin were effectively synthesized from GTP. On the other hand, when the phosphate was omitted 6-hydroxymethylpterin was formed.
The possible biosynthetic process of L-threo-neopterin was discussed.