Dimerization Site of Carp Myosin Heavy Chains by the Endogenous Transglutaminase

Abstract

Dimerization of carp myosin heavy chains at the initial stage of endogenous transglutaminase (TGase)-catalyzed cross-linking was investigated under the similar condition to that of setting in fish meat gelation, with 0.5M NaCl and 5mM CaCl₂ at pH 7.0 and 25°C.
Gel filtration chromatography and SDS-PAGE analyses showed that the enzymatic dimerization occurred intramolecularly between the heavy chains, independent of the thermal aggregation and a decrease in Ca-ATPase activity of myosin molecules, but myosin light chains were not cross-linked. The heavy chains were preferentially cross-linked in rod portion than in subfragment-1.
Monodansylcadaverine (MDC) inhibited completely the dimerization and was incorporated into myosin heavy chains. Chymotryptic digestion of the MDC-labeled myosin revealed that the labeled site was on the rod and heavy meromyosin (HMM) portions, but not on subfragment-1 or light meromyosin portions. Further chymotryptic digestion of MDC-labeled heavy meromyosin produced MDC-la-beled subfragment-2 (S2). All these results indicated the enzymatic dimerization site being located on S2 heavy chain portions of myosin molecule.