A number of laboratories have reported that animal mitochondria can actively accumulate various inorganic ions (8). Energy can be supplied by either substrate oxidation or ATP. The antibiotic, oligomycin, inhibits ATP-driven Ca uptake, but not substrate-driven uptake (6,18
Materials and MethodsIsolation of Mitochondria. Corn seeds (Zea mays L., WF9 X M14) were germinated in the dark at 28°on paper towels saturated with 10-4 M CaC2.After 3 and one-half days, the shoots were excised, chilled, and ground in an ice-cold mortar with 0.25 M sucrose, 0.05 M KH2PO4 and 0.005 M EDTA, adjusted to pH 7.5 with Tris (hydroxymethyl) aminomethane. The slurry was strained through cheesecloth. Mitochondria were isolated in a refrigerated centrifuge as the fraction sedimenting between 2000 X g for 5 minutes and 12,000 X g for 10 minutes. The mitochondria were twice washed, first in the grinding medium, next in 0.25 M sucrose and were finally suspended in 0.25 M sucrose. The mitochondria were quite active, giving QO2(N) values of about 1500 and P/O values of about 2.5 when oxidizing a mixture of pyruvate and succinate in the absence of inhibitors or uncouplers. Procedures for determining oxidative phosphorylation have been described (12