Biosynthesis of Pteridines and of Phenylalanine Hydroxylase Cofactor in Cell-free Extracts of Pseudomonas Species (ATCC 11299a)

From the ¹ From the Laboratory of Clinical Biochemistry, National Heart Institute, National Institutes of Health, Bethesda Maryland 20014

A cell-free system for the synthesis of a phenylalanine hydroxylase cofactor from guanosine triphosphate was obtained from extracts of Pseudomonas species (ATCC 11299a). This preparation produced formic acid from the ureido carbon of labeled GTP. The preparation also made specific pteridines from GTP. Among the products, xanthopterin, neopterin, and a cyclic phosphate derivative of neopterin were tentatively identified. These were probably present in a reduced form in the reaction mixtures. The requirements for cofactor synthesis include GTP, Mg⁺⁺, and a reduced triphosphopyridine nucleotide-generating system. Although the exact structure of the cofactor produced could not be determined, it was shown that a number of possible reduced pteridine products could serve as cofactors for the hydroxylase enzyme. Evidence is presented that the various reactions described are part of the over-all biosynthetic pathway for reduced pteridines which can serve as phenylalanine hydroxylase cofactors.

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