The stoichiometry of binding of the aurovertins to mitochondrial ATPases: revision of the molar absorption coefficient.

The purity of aurovertins A, B, and D, which inhibit the mitochondrial ATPase and show fluorescence enhancement when bound, has been determined by high-resolution proton nuclear magnetic resonance. This technique demonstrated that solvent molecules, especially water, are tightly bound to crystalline aurovertins B and D. The molar absorption coefficient for aurovertins A, B, and D at the longest wavelength maximum (367.5-369 nm) has been determined to be 38,500 liter x mol(-1) x cm(-1). This correct molar absorption coefficient should enable correct binding stoichiometries for aurovertin to ATPases to be determined.

Citreoviridin, a specific inhibitor of the mitochondiral adenosine triphosphatase.

1. Citreoviridin was a potent inhibitor of the soluble mitochondrial ATPase (adenosine triphosphatase) similar to the closely related aurovertins B and D. 2. Citreoviridin inhibited the following mitochondrial energy-linked reactions also: ADP-stimulated respiration in whole mitochondria from ox heart and rat liver; ATP-driven reduction of NAD+ by succinate; ATP-driven NAD transhydrogenase and ATPase from ox heart submitochondrial particles. 3. The dissociation constant (KD) calculated by a simple law-of-mass-action treatment for the citreoviridin--ATPase complex was 0.5--4.2micron for ox-heart mitochondrial preparations and 0.15micron for rat liver mitochondria. 4. Monoacetylation of citreoviridin decreased its inhibitory potency (KD=2--25micron, ox heart; KD=0.7micron, rat liver). Diacetylation greatly decreased the inhibitory potency (KD=60--215micron, ox heart). 5. Hydrogenation of citreoviridin monoacetate diminished its inhibitory potency considerably. 6. No significant enhancement of fluorescence was observed when citreoviridin interacted with the mitochondrial ATPase.