The Stoichiometry of Respiration-driven Potassium Transport in Corn Mitochondria

Determinations were made for corn (Zea mays L., WF9-Tms x M14) mitochondria of the stoichiometric relationship between K(+) transport and bond energy produced in respiration (K(+)/ approximately ratio). With inward pumping of potassium acetate activated by NADH oxidation, the initial rate of K(+) transported into the sucrose inaccessible space varied between 0.58 and 0.97 K(+)/ approximately , assuming 2 high energy bond equivalents per NADH oxidized. Only small amounts of H(+) were ejected. Valinomycin did not alter the ratio.Efflux pumping of K(+) in KCl media gave a K(+)/ approximately of 0.92. Substituting sucrose for KCl caused a drop in respiration and H(+) ejection, indicating a requirement for cation efflux pumping in acceptorless respiration. Valinomycin added to the KCl medium accelerated passive swelling but did not impair subsequent efflux pumping, although respiration was partially uncoupled.