β-actinin isoforms in various types of muscle and non-muscle tissues

We found that β-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 against β-actinin purified from adult chicken breast muscle (pectoralis major). One of the β-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 (designated βIII) that was found in the embryonic stages of skeletal muscle (Asami, Funatsu & Ishiwata (1988) J. Biochem. 103, 72-75) was present instead of βII in non-muscle tissues and blood. In cardiac and smooth muscles, βIII coexisted with βI and βII. The antibody of β-actinin did not cross-react to cytoplasmic β-actinin (molecular weight, 80, 000 daltons) found in kidney. It was suggested that the combination of βI and βIII 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 that β-actinin forms a genetic family whose constituents have an ability to cap either the pointed or barbed end of actin filaments.