The rates of isomerization for G-actin-S1 complexes are approximately 200 s-1 for GS and 50 s-1 for G2S at 4 degrees C, with GS being less efficiently dissociated than G2S by MgATP.
The study demonstrates that GS and G2S complexes display different kinetic behaviors in response to nucleotides, suggesting different mechanical properties of the cross-bridge correlate with different orientations of the myosin head.
The kinetics of interaction of monomeric pyrenyl-labeled G-actin with myosin subfragment-1 (S1 (A1) and S1(A2) isomers) has been examined in the stopped-flow at low ionic strength. The data confirm the previously reported existence of binary GS and ternary G2S complexes. The increase in pyrenyl-actin fluorescence which monitors the G-actin-S1 interactions is linked to the isomerization of these complexes following rapid equilibrium binding steps. The rates of isomerization are approximately 200 s-1 for GS and approximately 50 s-1 for G2S at 4 degrees C and in the absence of ATP. DNaseI and S1 bind G-actin essentially in a mutually exclusive fashion. Both GS and G2S are dissociated by MgATP and MgADP. The kinetics and mechanism of ATP-induced dissociation of G2S are quantitatively close to the ATP-induced dissociation of F-actin-S1, which indicates the G2S is a good model for the F-actin-S1 interface. GS and G2S display different kinetic behaviors in response to nucleotides, GS being less efficiently dissociated than G2S by MgATP. This result suggests that different mechanical properties of the cross-bridge might correlate with different orientations of the myosin head and different actin/myosin binding ratios.
Blanchoin et al. (Wed,) reported a other. Myosin subfragment-1 (S1) was evaluated on Kinetics of interaction and rates of isomerization. The rates of isomerization for G-actin-S1 complexes are approximately 200 s-1 for GS and 50 s-1 for G2S at 4 degrees C, with GS being less efficiently dissociated than G2S by MgATP.