A contribution of the mitochondrial adenosinetriphosphatase inhibitor protein to the thermal stability of the F0F1-ATPase complex.

A complete inactivation is observed after a 3 min pre-incubation at 70 degrees C with mitochondrial F0F1-ATPase complex depleted of the ATPase natural inhibitor protein (ammonium-Sephadex submitochondrial particles) and activated MgATP-submitochondrial particles (particles that after a 4 h-pre-incubation at 42 degrees C released the endogenous inhibitor protein). However, latent MgATP-submitochondrial particles (particles containing the inhibitor protein) pre-incubated under the same conditions are totally inactivated only after 15 min of pre-incubation. When ammonium-Sephadex particles are reconstituted with 20 micrograms/ml of purified ATPase inhibitor protein there is an increase of 15-fold in the half-time for thermal inactivation (t0.5), showing that the inhibitor protein protects the mitochondrial F0F1-ATPase complex against thermal inactivation.