ISOLATION AND PROPERTIES OF WHITE SKELETAL-MUSCLE ALPHA-ACTININ FROM SEA-TROUT (SALMO-TRUTTA) AND BASS (DICENTRARCHUS-LABRAX)

Fish alpha-actinin purified from sea-trout and bass white muscle by me ans of two different extraction procedures was used to investigate the eventual presence of different muscle isoforms in Z-disks. These fish alpha-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 alpha-actinin antibodies, suggesting a single molecular species. The role of fish alpha-actinin as an anchorage site for thin actin filaments and elastic titin filam ents in Z-bands was studied. Despite conservation of the actin-binding site, fish alpha-actinin has a better actin-binding ability (kD = 0.3 mu M) than chicken smooth muscle alpha-actinin (kD = 1.6 mu M). Sever al other structural and functional characteristics of fish alpha-actin in were also studied: conservation of sequence and domain structure, t he role of divalent ions (Ca2+, Mg2+) and the dielectric constant of t he medium in alpha-actinin-actin interaction. Although the reason for fish white muscle alpha-actinin's close affinity to actin was not clea rly established, our results suggested that the physicochemical enviro nment of the Z-filaments in Z-disks might be crucial.