The hydrolysis of myosin by a water-insoluble polyanionic derivative of trypsin (IMET) has been studied with the pH-stat and by sedimentation velocity experiments. As with soluble trypsin, the kinetic data can be interpreted in terms of two first-order reaction classes. However, in the case of IMET, the fast reaction no longer parallels the formation of the meromyosins, and the total number of peptide bonds available for enzymic hydrolysis is markedly reduced. The implication of these findings for the conformation of the linkage between the meromyosins is discussed.

Meromyosins formed by IMET have distinctive properties: Heavy meromyosin shows a 3 s component even when isolated from partially digested myosin. Light meromyosin can form lattice structures instead of fibrous aggregates.

The 3 s component, heavy meromyosin subfragment 2, has been isolated by alcohol fractionation, followed by isoelectric precipitation. This water-soluble protein has a molecular weight of 61,000 and a helix content of 80%. These values, together with the sedimentation velocity and viscosity data, suggest a length of about 400for the molecule. Heavy meromyosin subfragment 2 forms paracrystals with a 145periodicity.