Cell beta-actinin, an accelerator of actin polymerization, isolated from rat kidney cytosol.

A motility-regulatory protein called cell beta-actinin was isolated from rat kidney cytosol. Although its molecular weight (approximately 80,000) is different from that of beta-actinin from skeletal muscle (heterodimer of 34,000 and 37,000), the action on actin is the same for both. Cell beta-actinin accelerates polymerization of actin by enhanced nucleation resulting in shorter actin filaments, inhibits the reassociation of sonicated F-actin fragments, and forms a Mg polymer in the presence of Mg ions. Cell beta-actinin appears to be present in various tissues of rat, rabbit, chicken, and pig. Cell beta-actinin is thought to function as an accelerator of actin polymerization in nonmuscle cells, in which actin monomers are abundantly present.