Interaction of azide with beef heart mitochondrial ATPase

This study examined the inhibition of azide as a probe of the magnesium regulation of beef heart mitochondrial ATPase (F1) catalysis. Azide elicited a slow hysteretic effect on both ATP and ITP hydrolysis of F1. This hysteretic effect was shown to be due to the consecutive binding of magnesium and azide, and to be independent of catalytic turnover. The azide binding site was also shown to be separate from the anion binding HCO3- site on F1. The results presented indicate that metal binding is important in the inhibition of the hydrolytic activity and regulation of F1. A model is presented which is consistent with the hysteretic inhibition of F1 by azide, in which there is a slow equilibration between free enzyme and the enzyme-magnesium-azide complex.