Cyanide & chelating agent effects on in vitro CO2 fixation in sweet orange leaves

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Abstract
Cyanide, azide, and chelating agent effects on in vitro dark C14O2 fixation studies with ribose-5-phosphate and phosphoenolpyruvate (PEP) as substrates with preparations from sweet orange leaves were compared. Cyanide increased the fixation when added with the PEP during the incubation period. When added just before the acid that was used to stop reactions and expel unreacted bicarbonate, cyanide resulted in increased C14 counts on planchets for both substrates but the effect was much less than when present during the incubation. The major effect of cyanide appeared to be in stabilization of oxalacetate by formation of a cyanohydrin. The oxalacetate cyanohydrin was identified when the PEP substrate was used. Removing heavy metals did not alter the increased fixation resulting from cyanide. Cyanide overcame inhibitory effects of heavy metals when the latter were added to the PEP reaction system for Zn. In general the metal effects were on the reactions themselves rather than on metal-induced decarboxylation of products. The stimulating effect of a chelating agent on the reactions was additive with either cyanide or azide and occurred in a system cleaned of heavy metals by ammonium sulfate precipitation with ethyl-enediamine tetraacetic acid and dialysis.