Marsupial cardiac myosins are similar to those of eutherians in subunit composition and in the correlation of their expression with body size.

Cardiac myosins and their subunit compositions were studied in ten species of marsupial mammals. Using native gel electrophoresis, ventricular myosin in macropodoids showed three isoforms, V(1), V(2) and V(3), and western blots using specific anti-alpha- and anti-beta-cardiac myosin heavy chain (MyHC) antibodies showed their MyHC compositions to be alphaalpha, alphabeta and betabeta, respectively. Atrial myosin showed alphaalpha MyHC composition but differed from V(1) in light chain composition.

Myosin isoforms and fibre types in jaw-closing muscles of Australian marsupials.

Myosin heavy chains (MyHCs) and fibre types in the masseter muscle of seven species of Australian marsupials (brushtail and ringtail possums, bettong, bandicoot, dunnart, two species of antechinuses) spanning three orders were studied by native myosin electrophoresis, SDS-PAGE, immunoblotting and immunohistochemistry. We found only two fibre types in the masseter muscles of these animals: (1) masticatory fibres expressing masticatory MyHC, and (2) hybrid alpha/beta fibres that co-express alpha-cardiac and beta-cardiac MyHCs. Masticatory fibres predominate in most species, being appropriate for predation or for chewing tough vegetable matter.