Interactions between subunits a and b in the rotary ATP synthase as determined by cross-linking

► Interactions of subunits a and b of the rotary ATP synthase were examined. ► Cys substitutions were used for disulfide formation or with a bi-functional reagent. ► Cross-linked products indicated that one b subunit has contact with TM2 of subunit a. ► Additional cross-links were detected between subunits a and b and between b and c. ► A model is presented in which one b subunit is near aTM2 and the other is near aTM5.