Enzyme preparations from Escherichia coli catalyze the conversion of various species of 2-amino-4-hydroxy-6-(polyhydroxyalkyl)dihydropteridines to dihydropteroic acid. Of these compounds, the one utilized most efficiently by the enzyme system is 2-amino-4-hydroxy-6-(d-erythro-1',2',3'-trihydroxypropyl)dihydropteridine. Evidence is presented to show that the latter compound is converted by a heat-stable enzyme or enzymes to 2-amino-4-hydroxy-6-hydroxymethyldihydropteridine, a compound which is used directly as substrate for the formation of dihydropteroate and thus represents an intermediate in the conversion of the polyhydroxyalkyldihydropteridines to dihydropteroate. Evidence is presented which indicates that the enzyme system that catalyzes the synthesis of dihydropteroate from p-aminobenzoate and guanosine triphosphate will convert GTP to pteridine intermediates when p-aminobenzoate and ATP are left out of the reaction mixture. The pteridines that have been identified as products of this transformation are 2-amino-4-hydroxy-6-hydroxymethyldihydropteridine and 2-amino-4-hydroxy-6-(erythro-1',2',3'-trihydroxypropyl)dihydropteridine. Smaller quantities of the corresponding threo isomer of the latter compound are also made enzymatically from GTP, but the significance of the formation of this compound is not clear.
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Jones et al. (1967) studied this question.