Contractile proteins of fast and slow fibers during differentiation of lobster claw muscle.

Contractile protein populations were determined, using gel electrophoresis, during development of the claw closer muscles of the lobster Homarus americanus. In the adult the paired claw closer muscles are asymmetric, consisting of a crusher muscle with all slow fibers and a cutter muscle with a majority of fast and a few slow fibers. The electrophoretic banding pattern of these adult fast and slow fibers shows a similarity in the major proteins including myosin, actin, and tropomyosin which are common to both fiber types. Paramyosin is slightly heavier in fast fibers than in slow. However, fast fibers have three proteins and slow fibers have four proteins which are unique to themselves. Several of these unique proteins belong to the regulatory troponin complexes. In juvenile 4th stage lobster, where the paired closer muscles are undifferentiated, the banding pattern reveals the presence of proteins common to both fiber types including myosin, actin, and tropomysin but the conspicuous absence of all unique fast fiber proteins as well as one unique slow fiber protein. By the juvenile 10th stage most of these unique proteins are present except for one unique slow fiber protein. Thus lobster fast and slow fiber differentiation entails coordinate gene activation to add unique contractile proteins.