Molecular changes in myosin caused by methylmercuric hydrome

An ultracentrifugal study has been made on myosin treated with methylmercuric hydroxide. 1. 1. Myosin is transformed by tritration of its -SH groups with methylmerucuric hydroxide to a faster-sedimenting product. This occurs in the same range of methyl-mercuric hydroxide titration at which the calcium-activated ATPase activity is inhibited. A parallelism can be demonstrated between the loss of ATPhase activity and the loss of myosin due to the transformation process. 2. 2. Complete titration of the -SH groups of myosin with methylmercuric hydroxide causes the release of a small subunit with sedimentation rate of 1.6 S, at 25° but not at 15°. 3. 3. These results suggest that the -SH groups whose titration causes inactivation of ATPase activity are responsible for the configurational integrity of the active site, and that release of the small subunit is not related to titration of these -SH groups.