Fig. 5. Analysis of the myofibrillar protein isoform composition of lobster claw opener muscle by SDS–PAGE and western blotting. Fast (F), slow-twitch (S1) and slow-tonic (S2) fibres from lobster cutter claw closer, crusher claw closer and superficial abdominal muscles are provided for reference (lanes a–c, respectively). Claw opener fibres are arranged according to their position from most proximal (lane d) to most distal (lane i). (A) Silver-stained polyacrylamide gel showing myofibrillar proteins (MHC, myosin heavy chain; P, paramyosin; P75, 75 kDa protein; TnT, troponin-T; Ac, actin; Tm, tropomyosin; TnI, troponin-I). (B) Western blot probed with anti-TnT antibody. S2 fibres (lanes c–e, i) possess varying amounts of TnT1 (arrow), with higher levels in proximal fibres. (C) Western blot probed with anti-P75 antibody. Only fast fibres possess the P75 protein (lane a). (D) Western blot probed with anti-TnI antibody. Although not all five isoforms were detected at this loading, there were clear differences between F (lane a), S1 (lanes b, f–h) and S2 (lanes c–e, i) fibres. On the basis of this analysis, the proximal (lanes d, e) and distal (lane i) fibres were classified as S2, while central fibres (lanes f, g) were classified as S1. The positions of molecular mass standards are indicated on the left.