Isolation and Antigenic Characterization of Corn Mitochondrial F₁-ATPase

Abstract

Corn mitochondrial F(1)-ATPase was purified from submitochondrial particles by chloroform extraction. Enzyme stored in ammonium sulfate at 4 degrees C was substantially activated by ATP, while enzyme stored at -70 degrees C in 25% glycerol was not. Enzyme in glycerol remained fully active (8-9 micromoles P(i) released per minute per milligram), while the ammonium sulfate preparations steadily lost activity over a 2-month storage period. The enzyme was cold labile, and inactived by 4 minutes at 60 degrees C. Treatment with octylglucoside resulted in complete loss of activity, while vanadate had no effect on activity. The apparent subunit molecular weights of corn mitochondrial F(1)-ATPase were determined by SDS-polyacrylamide gel electrophoresis to be 58,000 (alpha), 55,000 (beta), 35,000 (gamma), 22,000 (delta), and 12,000 (epsilon). Monoclonal and polyclonal antibodies used in competitive binding assays demonstrated that corn mitochondrial F(1)-ATPase was antigenically distinct from the chloroplastic CF(1)-ATPases of corn and spinach. Monoclonal antibodies against antigenic sites on spinach CF(1)-ATPase beta and gamma subunits were used to demonstrate that those sites were either changed substantially or totally absent from the mitochondrial F(1)-ATPase.