51] Mitochondrial ATPase inhibitor: Properties and applications

Abstract

Publisher Summary Mitochondrial ATPase inhibitor has been isolated from beef heart, rat liver, and yeasts. Proteins with similar properties have been found in chloroplasts and bacteria as well as in myofibrils. Most procedures for the purification of the inhibitor take advantage of its high degree of stability to heat and to variations in pH. The inhibitor is highly sensitive to trypsin, a property that is commonly used to prepare inhibitor-free ATPase. Mitochondrial ATPase inhibitor lacks cysteine and tryptophan; ATPase inhibitors from spinach chloroplasts and Escherichia coli also lack tryptophan. The mitochondrial ATPase inhibitor is clearly distinct from the є subunit of F 1 based on amino acid composition and other properties. On the other hand, the chloroplast and E . coli inhibitors are thought to be identical with the є subunits of the corresponding ATPases. There is an extensive cross-reactivity between ATPase inhibitors and ATPases from various sources, including the myofibrillar troponin inhibitor (TNI) and actomyosin. However, this cross-reactivity does not seem to be general or even reciprocal. The inhibition of mitochondrial ATPase by mitochondrial ATPase inhibitor is noncompetitive or uncompetitive. A noncompetitive inhibition is also found in cross-reacting systems, for example, those consisting of TNI and ATPases from mitochondria or chloroplasts.