Opposite effects of alfa-actinin and of fructose 1,6-bisphosphate aldolase on the microfilament network. The role of orthophosphate revisited.

At pH 7.5, in the presence of 0.1 M KCl, 2 mM MgCl2 and 15 mM phosphate, the binding of 1 molecule of alfa-actinin for each strand of 1000 actin monomers doubles the apparent viscosity of an F-actin solution (12 microM as the monomer). Further binding of one molecule of aldolase for each strand of 280 actin monomers halves the apparent viscosity of the alfa-actinin-F-actin system without any desorption of alfa-actinin. The effect of aldolase is not hindered by the addition of 0.1 mM fructose 1,6-bisphosphate. It is shown that orthophosphate acts as a damper of the regulatory effect of fructose bisphosphate on the interaction between aldolase and microfilaments.