Studies on the structure of connectin in muscle.

Enzymic hydrolysis, followed by amino acid analysis, provided no evidence for the presence of epsilon-(gamma-glutamyl) lysine or other isopeptide crosslinks in connectin. Gel elecrrophoresis in the presence of sodium dodecyl sulphate did not reveal any difference in connectin between normal and lathyritic muscle, indicating that lysyl oxidase does not initiate cross-link formation in connectin. Although connectin may be covalently crosslinked by some unknown mechanism, the available evidence suggests that the subunit of MW approximately to 900 000 is synthesised as a single polypeptide chain. In developing fetal muscle, myosin heavy chains are apparent some weeks earlier than connectin. This, together with the known susceptibility of connectin to hydrolysis, suggests that connectin exists in an exposed environment rather than as a core to the thick filament.