A CONTRIBUTION OF THE MITOCHONDRIAL ADENOSINE-TRIPHOSPHATASE 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 ATPa se natural inhibitor protein (ammonium-Sephadex submitochondrial parti cles) and activated MgATP-submitochondrial particles (particles that a fter a 4 h-pre-incubation at 42 degrees C released the endogenous inhi bitor protein). However, latent MgATP-submitochondrial particles (part icles containing the inhibitor protein) pre-incubated under the same c onditions are totally inactivated only after 15 min of pre-incubation. When ammonium-Sephadex particles are reconstituted with 20 mu g/ml of purified ATPase inhibitor protein there is an increase of 15-fold in the half-time for thermal inactivation (t(0.5)), showing that the inhi bitor protein protects the mitochondrial F0F1-ATPase complex against t hermal inactivation.