The Biosynthesis of Folic Acid Compounds in Plants

V. Reaction Mechanism of the Dihydropteroate-synthesizing Enzyme from Pea Seedlings

Abstract

Dihydropteroate synthetase purified from pea seedlings catalyzed the formation of dihydropteroic acid from 2-amino-4-hydroxy-6-hydroxymethyldi-hydropteridine and p-aminobenzoic acid in the presence of ATP and Mg²⁺. The reaction was stimulated by preincubation of the enzyme with hydroxymethyldihydropteridine, ATP and Mg²⁺. AT³²P was incorporated into the enzyme frac tion by incubation with ATP-γ-³²P, hydroxymethyldihydropteridine and Mg²⁺. Dihydropteroic acid was formed and pyrophosphate was liberated by the incubation with p-aminobenzoic acid from the AT³²P-incorporated enzyme solution. AMP was detected as the other product in the reaction.
The proposed systematic name of dihydropteroate synthetase is discussed.