Effects of Hydroxamic Acids Isolated from Gramineae on Adenosine 5′-triphosphate Synthesis in Chloroplasts

Abstract
Two hydroxamic acids isolated from maize [Zea mays cv. LH Rinconada] extracts, 2,4-dihydroxy-7-methoxy-1,4-(2H)-benzoxazin-3(4H)-one (DIMBOA) and the 2-O-.beta.-D-glucopyranoside of DIMBOA, inhibit photophosphorylation by spinach [Spinacia oleracea] chloroplasts. Both cyclic and noncyclic photophosphorylations were inhibited to the same extent. The concentrations producing 50% inhibition for DIMBOA and its glucoside were about 1 and 4 mM, respectively. These compounds inhibit coupled electron transport but do not affect basal or uncoupled electron transport. Both acids inhibit the ATPase activities of membrane-bound coupling factor 1 (CF1) and of purified CF1. Apparently, DIMBOA and its glucoside act as energy transfer inhibitors of photophosphorylation.