Purification and characterization of an ATPase inhibitor protein from buffalo mitochondria.

A heat stable, 12kDa protein was purified to homogeneity from buffalo heart mitochondria. It suppressed hydrolytic activity of membrane bound mitochondrial ATPase and its functional activity was Mg++ and ATP dependent. Maximal inhibition was achieved at slightly acidic pH. Its ability to inhibit ATP hydrolysis was significantly diminished at alkaline pH and high ionic strength and the purified protein had a tendency to aggregate under such conditions. Circular dichroism (CD) studies revealed that the protein undergoes reversible changes in secondary structure from a predominantly alpha-helical form at alkaline pH to a beta-sheet structure at slightly acidic pH. These distinctly different conformations could be correlated with functionally 'inactive' and 'active' forms.