Résumé
Fish a-actinin purified from sea-trout and bass white muscle by means of two different extraction procedures was used to investigate the eventual presence of different muscle isoforms in Z-disks. These fish α-actinins have the same apparent molecular weight (100 kDa) and the same isoelectric point (pI = 5.6), and also have a total antigenic identity towards anti-bass and anti-chicken α-actinin antibodies, suggesting a single molecular species. The role of fish α-actinin as an anchorage site for thin actin filaments and elastic titin filaments in Z-bands was studied. Despite conservation of the actin-binding site, fish α-actinin has a better actin-binding ability (kD = 0.3 μM), than chicken smooth muscle a-actinin (kD = 1.6 μM). Several other structural and functional characteristics of fish α-actinin were also studied: conservation of sequence and domain structure, the role of divalent ions (Ca2+, Mg2+) and the dielectric constant of the medium in α-actinin-actin interaction. Although the reason for fish white muscle a-actinin's close affinity to actin was not clearly established, our results suggested that the physicochemical environment of the Z-filaments in Z-disks might be crucial.