We found thatβ-actinin isoforms are present in various types of tissues in adult chicken by using immunoblotting after two dimensional gel electrophoresis; for this purpose, an antibody was raised againstβ-actinin purified from adult chicken breast muscle (pectoralis major). One of theβ-actinin subunits,βI, was present in all tissues we examined,i.e.skeletal (pectoralis major, semitendinosus, and anterior latissimus dorsi), cardiac, and smooth (gizzard) muscles, non-muscle (brain, liver, and kidney) tissues and blood, whereas another subunit,β11, was present only in muscle tissues. A new subunit (designatedβIII) that was found in the embryonic stages of skeletal muscle (Asami, FunatsuIshiwata (1988)J. Biochem. 103, 72–75) was present instead ofβII in non-muscle tissues and blood. In cardiac and smooth muscles,βIII coexisted withβI andβII. The antibody ofβ-actinin did not cross-react to cytoplasmicβ-actinin (molecular weight, 80, 000 daltons) found in kidney. It was suggested that the combination ofβI andβIII present in non-muscle tissues and blood is identical to the barbed end capping protein isolated from brain by Killiman and Isenberg (EMBO J.1,889–894 (1982)). It is likely thatβ-actinin forms a genetic family whose constituents have an ability to cap either the pointed or barbed end
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