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Articles

The Stoichiometry of Respiration-driven Potassium Transport in Corn Mitochondria ¹

^a Department of Botany, University of Illinois, Urbana, Illinois 61801

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⁺/ 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⁺/, 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⁺/ 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.

³ Present address: Department of Botany, Imperial College of Science and Technology, Prince Consort Road, London, SW7, England.

¹ Supported by United States Atomic Energy Commission Contract AT 11-1-790.