ALPHA-ACTININS FROM CHICKEN SKELETAL-MUSCLE AND SMOOTH-MUSCLE SHOW CONSIDERABLE CHEMICAL AND IMMUNOLOGICAL DIFFERENCES

Highly purified α‐actinins from chicken fast skeletal muscle (breast) and chicken smooth muscle (gizzard) were compared both biochemically and immunologically. Analysis of the soluble tryptic peptides by two‐dimensional fingerprints showed that the two α‐actinins show major differences. Antiserum raised against each α‐actinin reacted strongly in double‐diffusion analysis with its own antigen, but not with the other α‐actinin. Thus, both at the level of peptide maps and of immunological cross‐reactivity, the two α‐actinins show considerable differences. Despite these differences both α‐actinins share a number of properties. Both consist of subunits which migrate as polypeptides of molecular weight 100000 on polyacrylamide gels in the presence of dodecylsulfate. Limited sequence homology was detected when peptides with similar mobilities in the tryptic fingerprints were analyzed for their amino acid composition. Proteolytic digestion of either native α‐actinin by trypsin or thermolysin yielded a protease‐resistant core of molecular weight about 55000. Both α‐actinins are thin rod‐shaped molecules when observed in the electron microscope. Thus, their similar shape and the existence of a protease‐resistant core argues that the different α‐actinins have similar overall secondary and tertiary structure. In addition immunological cross‐reaction could be detected by the sensitive indirect immunofluorescence microscopy technique. Antibodies to gizzard α‐actinin were found to stain the Z‐lines of skeletal muscle myofibrils, i.e. the known location of skeletal muscle α‐actinin. We discuss these differences found for α‐actinin from two muscle types in terms of differences found for other muscle proteins. Copyright © 1979, Wiley Blackwell. All rights reserved