Polymorphism of α‐Actinin

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Abstract
Heterogeneity of .alpha.-actinins from rabbit skeletal muscles was studied. Polyacrylamide gel electrophoresis in the presence and absence of sodium dodecyl sulfate made it possible to distinguish 2 closely related .alpha.-actinins from rabbit fast, white muscle. One isoprotein (designated type I .alpha.-actinin) appears to be preferentially located in the psoas muscle, while the other (designated type II .alpha.-actinin) appears to be preferentially located in the longissimus dorsi muscle. Electrophoretic analyses have shown that the 2 isoproteins are present as mixtures in most rabbit white, fast-twitch muscles. A standard polyacrylamide gel-sodium dodecyl sulfate/polyacrylamide gel sequential electrophoretic procedure was developed to resolve the different .alpha.-actinin dimers and to determine their subunit compositions. By this technique, both type I and type II .alpha.-actinins appeared to be homodimers. No heterodimeric species of .alpha.-actinin were detected. .alpha.-Actinin of red, slow-twitch muscles was similar to type II .alpha.-actinin of fast, white muscle on 1-dimensional and 2-dimensional gels. Slow, red muscle .alpha.-actinin was significantly different from fast, white muscle .alpha.-actinins in terms of 1-dimensional peptide mapping and immunological cross-reactivity.