Alcohol-induced biphasic inhibition of myosin subfragment 1 K-EDTA-ATPase

Butanol-induced inhibition of K-EDTA-ATPase of myosin subfragment 1 proceed ed by biphasic kinetics, consisting of rapid and slow inactivations. The ex tent of the rapid inactivation, which was estimated by extrapolating the pr ocess of slow inactivation to zero time of the incubation period, was satur ated with butanol concentration. Recovery of activity by dilution in the ra pid phase indicates that the rapid process is reversible. The slow inactiva tion was concomitant with a partial denaturation of the 50 kDa domain of S1 . which was detected by limited tryptic digestion. Other alcohols (methanol , ethanol, propanol and hexanol) also inhibited the K-EDTA-ATPase in the ra pid phase. The K-1, decreased with an increase in the number of methylene g roups of alcohol. When Ii-EDTA-ATPase activity in the rapid phase was plott ed against viscosity, surface tension or dielectric constant, the curves we re different for each of the various alcohol solutions. The rapid inactivat ion appears to be caused by a binding of the alkyl group to S1, rather than by solvent effects.. The kinetics of rapid butanol inhibitions indicate th at butanol reduces the maximum activity of ATPase but enhances an apparent affinity of S1 with ATP. These indications suggest that alcohol stabilizes S1.KATP intermediate. The rapid K-EDTA-ATPase inhibition was observed at th e same alcohol concentration where S1 Mg-ATPase was activated. (C) 1999 Els evier Science B.V. All rights reserved.