ALPHA-ACTININ FROM CHICKEN GIZZARD - AT LOW-TEMPERATURE, THE ONSET OFACTIN-GELLING ACTIVITY CORRELATES WITH ACTIN BUNDLING

The effect of alpha-actinin from chicken gizzard on the properties of F-actin solutions at 37 degrees C and at 4 degrees C was investigated. Beside the well-known increase of the gelling activity of alpha-actin in, it was found that lowering temperature to 4 degrees C: (a) modifie s the shape of the alpha-actinin-F-actin binding isotherm; (b) increas es the light scattering of the alpha-actinin-F-actin mixtures; (c) ind uces the formation of ribbons and bundles of F-actin. It was also obse rved that, by warning to 37 degrees C, the bundles of F-actin formed a t 4 degrees C were dissociated into quasi-parallel actin filaments run ning at a distance of 25-42 nn from each other. On subsequent cooling to 4 degrees C, these parallel filaments were rapidly assembled into b undles. As at 37 degrees C, alpha-actinin displays a potent gelling ac tivity on bundles but not on filaments of actin, and as the gelling ac tivity at 4 degrees C is accompanied by the formation of actin bundles , it is concluded that actin bundling is a necessary condition to prom ote the actin-gelling activity.