Pre-steady-state properties of bovine heart mitochondrial ATPase: a nucleotide-dependent H+ burst

The transient kinetics of bovine heart mitochondrial ATPase (F1) depleted of loosely bound nucleotides were observed. The activation process which was shown as a lag time before steady-state hydrolysis observed previously (Clark et al. (1984) Arch. Biochem. Biophys. 233, 378-392) was preceded by a proton burst when F1 was stripped of its loose nucleotides. 5'-Adenylylimidodiphosphate (Ado PP[NH]P) or MgATP binding is shown to cause proton release. maximum proton release per F1 free of loosely bound nucleotides is observed with MgATP. Modification with NBD-CL of F1 that was nucleotide-depleted eliminated the proton burst, which suggests that the modified tyrosine (i.e., in the catalytic subunit) is directly involved in the release of protons.