We have determined the hydrodynamic properties of detergent-solubilized ATPase, which is coupled to H+ pumping in bovine adrenal chromaffin granules, by sedimentation equilibrium centrifugation and gel permeation chromatography. The protein solubilized with detergent containing phosphatidylserine sediments as a particle of 264000 daltons and partial specific volume 0.829 cm3/g. Assuming a protein v of 0.73 and using the v measured for detergent and lipid mixed micelles of 0.93 cm3/g, we calculated that the protein component has a mass of 134000 daltons and that the equivalent of approximately 1.5 micelles of detergent are bound per particle. The particle exhibits a Stokes radius of 43 A, which, together with the calculated particle volume, indicates an axial ratio close to 1. We conclude that the ATPase is an intrinsic membrane protein with a structure very different from that of mitochondrial F1Fo ATPase.
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