Abstract
The biosynthesis of the pteridine moiety from guanine nucleotides was investigated in green leaves by following its enzymatic conversion to dihydropteroic acid. Various synthetic substances were compared for their efficacy of being incorporated into dihydropteroic acid in the presence of cell free system from green leaves ; the substances chosen were those having been supposed by Weygand et al. in insects and those postulated by others in microorganisms to serve as intermediates in the biosynthesis of the pteridine. The experimental results allowed to postulate that the pathway from guanine nucleotides to dihydropteroic acid in green leaves involves the reaction sequence ; guanine nucleotides→2-amino-4-hydroxy-6-(D-erythrotrihydroxypropyl) dihydropteridine→2-amino-4-hydroxymethyldihydropterid ine→its pyrophosphate ester. Adenosine triphosphate, magnesium ion and p-aminobenzoate were found as essential factors in these conversion reactions. Additional evidences supporting the postulated pathway were provided from the inhibition studies ; the analogs closely related to the substrates were found to inhibit the reaction acting respectively on different three steps in the reaction sequence. The biosynthetic pathway of the pteridine in green leaves are postulated which is essentially indifferent from that having been established for the microbial system.
