Reversal of 3-(3,4-Dichlorophenyl)-1,1-Dimethylurea Inhibition of Carbon Dioxide Fixation in Spinach Chloroplasts and Protoplasts by Dicarboxylic Acids

Abstract
3-(3,4-Dichlorophenyl)-1,1-dimethylurea (DCMU) inhibition of 14CO2 fixation in isolated intact spinach (Spinacia oleracea L.) chloroplasts was reversed (by about 34%) by L-malate but not by oxaloacetate (OAA). OAA reversed the DCMU inhibition in spinach protoplasts indicating an extrachloroplastic enzyme requirement. Extrachloroplastic OAA reduction was coupled with external dihydroxyacetone phosphate (DHAP) oxidation, and the malate formed might then enter the chloroplasts. Using ruptured protoplasts, the export of recently formed 3-phosphoglyceric acid (PGA) out of chloroplasts in exchange for external DHAP was apparently reversed by excess OAA. The PGA/DHAP shuttle across the chloroplast envelope was regulated by the external concentrations of DHAP and OAA.

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