Preferential binding of alpha-actinin to actin bundles

At 37 degrees C, the alpha-actin-F-actin binding isotherm is anomalous. In 6.7% polyethylene glycol 6000, concomitantly with the formation of actin bundles, the binding isotherm becomes hyperbolic (Kdiss. = 11.3 microM). alpha-Actinin increases the rigidity of the networks formed by actin bundles in polyethylene glycol and by paracrystalline actin in 16 mM MgCl2 but not by F-actin. It is proposed that in the cell alpha-actinin functions are mostly carried on by interaction with actin bundles.