Interactions of beef heart mitochondrial adenosine triphosphatase and aurovertin.

Aurovertin forms a complex with soluble beef heart mitochondrial ATPase (F₁) while exhibiting a biphasic fluorence enhancement. The effect of substrate, activators and inhibitors of F₁¹ of the fluorescence of the aurovertin-F₁ complex is reported. The aurovertin-F₁ complex can exist in two different states, one showing low fluorescence and the other with high fluorescence. Transition into the low fluorescence state is induced by various nucleoside triphosphates (ATP ± Mg²⁺, ITP ± Mg²⁺, GIP + Gg²⁺, and AMP-P(NH)P ± Mg²⁺). The rate and extent of fluorescence decrease caused by nucleotide addition (except that caused by ATP) is dependent on the presence of added Mg²⁺. The inhibitors of ATPase activity (AMP-P(NH)P, GMP-P(NH)P and EDTA) at concentrations that inhibit hydrolysis of ATP did not prevent the ATP induced decrease of aurovertin fluorescence. EDTA at high concentration (>0.4 mM) enhanced the effect of ADP.The complex of aurovertin with F₁ that had previously been treated with butanedione loses sensitivity to ATP. Addition of ADP to the system containing butanedione-treated enzyme caused a 2-fold greater enhancement of fluorescence than the addition of ADP to the control system. In contrast to the butanedione-treated enzyme, the complex of aurovertin with F₁ previously treated at pH 5.6 loses sensitivity to ADP. Addition of ATP to this system lowered the fluorescence as in the system containing native enzyme.On the basis of the analyses of the aurovertin fluorescence changes and hydrolytic activity of F₁, the existence of several types of ligand binding sties with varying degrees of specificity are proposed. It is further proposed that these sites are important in control of the conformation and the catalytic properties of the ATPase molecule.