Identification of high molecular weight proteins in squid muscle by Western blotting analysis and postmortem rheological changes

The high molecular weight protein connectin (also called titin) in Japanese common squid (Todarodes pacificus) mantle muscle was identified by western blotting analysis with 3B9, the mouse anti-chicken skeletal muscle connectin monoclonal antibody. Similarly to vertebrate samples, there exists connectin in invertebrate squid mantle muscle, and the amino acid sequences are assumed to resemble those present in the A band of vertebrate connectin, judging by the specificity of 3B9. Moreover, the connectin in squid muscle migrated in this study as a closely spaced doublet of alpha and beta (titins 1 and 2). Between 5 and 7 h post-mortem, the SDS PAGE patterns of the squid sample indicated a change of the doublet bands into a single beta-connectin band. Simultaneously, the rheological properties of the squid muscle changed substantially. This degradation of alpha-connectin into beta-connectin in the muscle can explain the critical change that occurs during the post-mortem tenderization of squid muscle.