Studies in the Metabolism of Plant Cells XII. Ionic Effects on Oxidation of Reduced Diphosphopyridine Nucleotide and Cytochrome C by Plant Mitochondria

Abstract

Some effects of ions on the mitochondrial oxidation of reduced diphospho. pyridine nucleotide (DPNH) and cytochrome c were studied. Potassium, sodium, magnesium, .calcium, chloride, and orthophosphate consistently increased the rate of DPNH oxidation of beetroot mitochondria which had been isolated in a medium of O· 4M sucrose containing ethylenediaminetetraacetic acid and tris(hydroxymethyl). aminomethane and washed in sucrose solution; the assay of DPNH oxidation was carried out in a O· 4M sucrose medium. The rate of DPNH oxidation was increased by increasing concentration of chlorides but decreased at higher concentrations. The optimum for divalent chloricles was lower than that for monovalent but the Ji~OLbli0" W':'O not marked when considered on the basis of ionic strengths. The optimal salt concentrations for stimulation of DPNH oxidation were much lower than those for stimulation of cytochrome c oxidation. It is concluded that this effect of salt on DPNH oxidation by mitochondria could explain salt respiration in plant tissue.