Dictyostelium myosin II G680V suppressors exhibit overlapping spectra of biochemical phenotypes including facilitated phosphate release

We have biochemically characterized 13 intragenic suppressors of the G680V mutation of Dictyostelium myosin II. In the absence of the G680V mutation, the suppressors result in a number of deviant behaviors, most commonly an i ncrease in the basal (actin-independent) ATPase of the motor. This phenotyp e is complementary to that of the G680V mutant and supports our proposal th at the latter impairs phosphate release. Different subsets of the mutants a lso suffer from poor ATPase enhancement by 1 mg/ml actin, failure to releas e from actin in the presence of ATP gamma S (or ADP and salt), and excessiv e release from actin in the presence of ADP. The patterns of suppressor beh aviors suggest that, in general, they are facilitating P-i-releasing state( s) of the motor, but that different individual suppressors may secondarily perturb other states or actions of the motor.