The stimulation of the ATPase activity of Escherichia coli F1-ATPase by the detergent lauryldimethylamine oxide (LDAO) and the relationship of this activation to removal of the inhibitory t subunit were studied. The detergent caused a dramatic decrease in the affinity of ∊-depleted enzyme for ∊ subunit, suggesting that release of ∊ is involved in LDAO activation. However, even in the absence of any ∊ subunit, the detergent caused a 140% increase in activity, indicating activation by effects independent of ∊ In contrast, the addition of 30% ethylene glycol to the reaction buffer caused a modest inhibition of the ATPase activity of ∊-depleted F1-ATPase but rendered the enzyme insensitive to inhibition by ∊ subunit. This solvent prevented the cross-linking of ∊ to ß by a water-soluble carbodiimide, although ∊ remained linkable to both ß and γ by dithiobis(succinimidyl propionate). Thus, ∊ was not dissociated from F1-ATPase, but its intimate interaction with the ß subunit was altered. These results suggest that the inhibitory action of ∊ is expressed through its interaction with ß. Kinetic analysis revealed that LDAO activated hydrolysis at both the high- and low-affinity promotional sites, with little change in Km values. Ethylene glycol caused a substantial increase in Km at the low-affinity promotional site and made the enzyme resistant to inhibition by aurovertin D. © 1990, American Chemical Society. All rights reserved.
