title: Use of stable analogs of myosin ATPase intermediates for kinetic studies of the "weak" binding of myosin heads to F-actin.
abstract: It is known that ternary complexes of myosin subfragment 1 (S1) with ADP and the Pi analogs beryllium fluoride (BeFx) and aluminum fluoride (AlF4-) are stable analogs of the myosin ATPase intermediates M* x ATP and M** x ADP x Pi, respectively. Using kinetic approaches, we compared the rate of formation of the complexes S1 x ADP x BeFx and S1 x ADP x AlF4- in the absence and in the presence of F-actin, as well as of the interaction of these complexes with F-actin. We show that in the absence of F-actin the formation of S1 x ADP x BeFx occurs much faster (3-4 min) than that of S1 x ADP x AlF4- (hours). The formation of these complexes in the presence of F-actin led to dissociation of S1 from F-actin, this process being monitored by a decrease in light scattering. The light scattering decrease of the acto-S1 complex occurred much faster after addition of BeFx (during 1 min) than after addition of AlF4- (more than 20 min). In both cases the light scattering of the acto-S1 complex decreased by 40-50%, but it remained much higher than that of F-actin measured in the absence of S1. The interaction of the S1 x ADP x BeFx and S1 x ADP x AlF4- complexes with F-actin was studied by the stopped-flow technique with high time resolution (no more than 0.6 sec after mixing of S1 with F-actin). We found that the binding of S1 x ADP x BeFx or S1 x ADP x AlF4- to F-actin is accompanied by a fast increase in light scattering, but it does not affect the fluorescence of a pyrene label specifically attached to F-actin. We conclude from these data that within this time range a "weak" binding of the S1 x ADP x BeFx and S1 x ADP x AlF4- complexes to F-actin occurs without the subsequent transition of the "weak" binding state to the "strong" binding state. Comparison of the light scattering kinetic curves shows that S1 x ADP x AlF4- binds to F-actin faster than S1 x ADP x BeFx does: the second-order rate constants for the "weak" binding to F-actin are (62.8 +/- 1.8) x 10(6) M-1 x sec-1 in the case of S1 x ADP x AlF4- and (22.6 +/- 0.4) x 10(6) M-1 x sec-1 in the case of S1 x ADP x BeFx. We conclude that the stable ternary complexes S1 x ADP x BeFx and S1 x ADP x AlF4- can be successfully used for kinetic studies of the "weak" binding of the myosin heads to F-actin.
authors.affiliation: Bach Institute of Biochemistry, Russian Academy of Sciences, Moscow, 117071, Russia. inbio@glas.apc.org
authors.forename: E V
authors.initials: EV
authors.lastname: Rostkova
authors.forename: L N
authors.initials: LN
authors.lastname: Moiseeva
authors.forename: M V
authors.initials: MV
authors.lastname: Teplova
authors.forename: O P
authors.initials: OP
authors.lastname: Nikolaeva
authors.forename: D I
authors.initials: DI
authors.lastname: Levitsky
mesh_terms: D000199:Actins / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D007700:Kinetics; D008956:Models, Chemical; D018482:Muscle, Skeletal / Q000378:metabolism; D009218:Myosins / Q000737:chemistry* / Q000378:metabolism*; D011817:Rabbits
chemical_list: D000199:Actins; D009218:Myosins