Stripping of proteins from submitochondrial particles of rat skeletal muscle or bovine heart by chemical uncouplers

Abstract

Proteins of similar molecular weights were stripped from submitochondrial particles (A particles) of rat skeletal muscle or bovine heart by treatment with classical chemical uncouplers at 0 degrees C as with Ca2+. Proteins released included two of high molecular weight (about 43 000 and 30 000), an ATPase inhibitor protein (IF1) as well as the Ca2+-binding lipoprotein that has previously been shown to protect the mitochondrial ATPase complex against inhibition by N,N'-dicyclohexylcarbodiimide (DCCD). The latter two proteins were purified to a high degree. The crude fraction obtained by stripping with chemical uncouplers also contained traces of an additional protein (relative mass (Mr) approximately 13 000) which was also found upon aging of the crude fraction stripped by Ca2+. It was not found in aged preparations of either purified IF1 or the lipoprotein, but appeared when IF1 and the lipoprotein were mixed and aged together. Pretreatment of the mixture with 2-mercaptoethanol prior to electrophoresis did not remove the hybrid. More phospholipid was stripped from A particles by chemical uncouplers than by Ca2+ but less protein was stripped. Phosphatidylcholine, phosphatidylethanolamine, lysophosphatidylcholine, and cardiolipin were identified in the phospholipid fractions.