The Purification, Characterization and Localization of β‐Actinin from Chicken Muscle

β‐Actinin was purified to homogeneity from water extracts of chicken leg muscle by chromatography on DEAE‐cellulose and gel filtration on Sephadex G‐200. 60–100 mg of protein was obtained from 1 kg of muscle. The molecular weight estimated from gel electrophoresis in the presence of sodium dodecylsulfate was 65000, from gel filtration on Sephadex G‐200 66000, and from sedimentation equilibrium experiments 67000. The results show that β‐actinin is a monomeric protein. The amino acid composition was determined and differed from β‐actinin of rabbit muscle. Double‐immunodiffusion experiments in Ouchterlony plates using anti‐chicken β‐actinin indicated that an immunologically indistinguishable form of this protein is present in muscle and non‐muscle tissues of the chicken. The distribution of β‐actinin is therefore similar to G‐actin and parvalbumin‐like protein. β‐Actinin was found to accumulate in differentiating primary muscle cell cultures after 120 h approximately together with myosin and actin, proteins necessary for myofibril assembly and functioning. Experiments to investigate the localization of β‐actinin, using the indirect immunofluorescence technique, showed a regular, intensive cross‐striation pattern within the I band of isolated myofibrils. An electronmicroscopic investigation demonstrated that β‐actinin does not polymerize to filamentous structures under conditions where G‐actin is transformed to F‐actin. It is able to inhibit the polymerization of G‐actin and promotes the depolymerization of preformed F‐actin filaments in vitro . The immumological, physico‐chemical and electronmicroscopic data show that β‐actinin is a quite distinct protein from actin.