Using 2′(3′)‐O‐Trinitrophenyl Derivatives of Adenine Nucleotides to Study the Structure and Mechanism of Functioning of Soluble Mitochondrial ATPase

Abstract

The 2''(3'')-O-trinitrophenyl (N3ph) derivatives of the adenine nucleotides are strong competitive inhibitors of isolated mitochondrial ATPase (factor F1). Ki decreases in the order N3phAdo > N3phAMP > N3phADP and is equal to 8 nM for N3phADP. Picric acid, which activates the ATPase reaction of factor F1 without changing the Km(app.), prevents the inhibiting action of N3phADP. At pH 7.6 the inhibition of factor F1 is accompanied by the binding of 1 molecule of N3phADP to a molecule of the enzyme. This binding leads to changes in the absorption spectrum, but not in the intensity of the fluorescence of the N3phADP. At pH 6.7 1 or 2 molecules of N3phADP bind with the tight binding sites of factor F1. This binding is accompanied by the manifold enhancement of the fluorescence of N3phADP. The sites of factor F1 that tightly bind nucleotides are probably immersed in the hydrophobic pocket of the protein molecule.