Polymorphism of α‐Actinin

Heterogeneity of α‐actinins from rabbit skeletal muscles was studied. Polyacrylamide gel electrophoresis in the presence and absence of sodium dodecyl sulfate has made it possible to distinguish two closely related α‐actinins from rabbit fast, white muscle. One isoprotein (designated type I α‐actinin) appears to be preferentially located in the psoas muscle, while the other (designated type II α‐actinin) appears to be perferentially located in the longissimus dorsi muscle. Electrophoretic analyses have further shown that the two 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 α‐actinins dimers and to determine their subunit compositions. By this technique, both type I and type II α‐actinins appeared to be homodimers. No heterodimeric species of α‐actinin were detected. α‐Actinin of red, slow‐twitch muscles was similar to type II α‐actinin of fast, white muscle on one‐dimensional and two dimensional gels. However, slow, red muscle α‐actinin was significantly different from fast, white muscle α‐actinins in terms of one‐dimensional peptide mapping and immunological cross‐reactivity.