Photosynthetic CO(2)-fixation in isolated pea (Pisum sativum L., cv Little Marvel) chloroplasts during induction is markedly inhibited by 0.4 millimolar sulfite. Sulfate at the same concentration has almost no effect. The (14)CO(2)-fixation pattern indicates that the primary effect of sulfite is inhibition of the reaction catalyzed by ribulose bisphosphate carboxylase and a stimulation of export of intermediates out of the chloroplasts. Inhibition of light modulation of stromal enzyme activity does not appear to account for the toxicity of SO(2) in this Pisum variety. Arsenite at 0.2 millimolar concentrations inhibits light activation and inhibits photosynthetic CO(2) fixation. The (14)CO(2)-fixation pattern indicates that the primary effect of arsenite is inhibition of light activation of reductive pentose phosphate pathway enzyme activity.
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