Homologous and Heterologous Inhibitory Effects of ATPase Inhibitor Proteins on F-ATPases*

(IF1, STF1, and STF2) appear to be involved in the regu-lation of ATP synthase. Both IF1 and STF1 inhibit F1, whereas the proposed function for STF2 is to facilitate the binding of IF1 and STF1 to F1. The oligomerization properties of yeast IF1 and STF1 have been investigated by sedimentation equilibrium analytical ultracentrifu-gation and by covalent cross-linking. Both techniques confirm that IF1 and STF1 oligomerize in opposite direc-tions in relation to pH, suggesting that both proteins might regulate yeast F1F0-ATPase under different con-ditions. Their effects on bovine F-ATPases are also de-scribed. Whereas bovine IF1 inhibits yeast F1-ATPase even better than yeast IF1 or STF1, the capability of yeast IF1 to inhibit the bovine enzyme is very low and decreases with time. Such an effect is also observed i