[Interconnection between the two-stage kinetics of actomyosin Mg2+-ATPase and breaks in Arrhenius plots]

It has been shown that breaks in Arrhenius plots take place only when the two-stage mechanism of actomyosin ATPase is realized. Removal of two-stage behavior of ATPase leads to the strengthening of Arrhenius plots. It can be achieved by decomposition of two-stage kinetic curves into two one-stage (higher and lower temperature) constituent curves, or by "switching off" ATPase reaction over one of the two one-stage mechanisms by changing KC1 or ATP concentrations. In both cases Arrhenius plots are linear and Ea values, as well as maximal ATPase activity for higher temperature mechanism are twice as much as those for the lower temperature mechanism. On the contrary, non-linear Arrhenius plots show the lowering of Ea with an increase of temperature. We conclude that the breaks in Arrhenius plots can be due to the shift of equilibrium between two one-stage mechanisms of actomyosin ATPase, whose simultaneous course leads to the two-stage kinetics of this reaction.