Role of SH_a in the Polymerization of Myosin Heavy Chain during Ice Storage of Carp Actomyosin

Abstract

The surface SH content of carp actomyosin decreased in a similar way to the total SH content during ice storage, regardless of the presence of sorbitol, as well as the formation of myosin heavy chain (MHC) dimer, indicating that the surface SH groups in myosin molecules were responsible for the oxidation of actomyosin.
The Ca²⁺-ATPase activity of actomyosin stored in the presence or absence of sorbitol was enhanced by the NEM modification of SH groups. EDTA-ATPase activity was stable during the storage despite the presence of sorbitol. These results indicate that reactive SH, SH₁, in myosin head was not oxidized.
The increase of Mg²⁺ (EGTA)-ATPase activity suggests that SH_a on the tail portion of myosin participates in oxidation during storage, no matter whether sorbitol was added or not.
These findings suggest that SH_a on the myosin tail portion, not SH₁ on the myosin head portion, is responsible for the oxidation of MHC and the formation of its dimer.