Isolation and characterization of a kettin-like protein from crayfish claw muscle

A 540 kDa protein was isolated from crayfish claw muscle (closer). The secondary structure mainly consisted of beta-sheet (70%). The rotary shadowed images were long filaments, 300-360 nm long. It is localized in the sides of the Z-lines extending to the I band and elongatable upon stretch of muscle. Immunological crossreactivities strongly suggested that this protein corresponds to kettin (500-700 kDa) of insect striated muscle. In view of molecular shape and secondary structure, and immunological crossreactivities, it is suggested that this kettin-like protein belongs to connectin/titin family of striated muscle.