Biochemical susceptibility of myosin in chicken myofibrils subjected to hydroxyl radical oxidizing systems

Biochemical changes of myosin in chicken myofibrils exposed to nonenzymatic, hydroxyl radical generation systems (HRGS) were investigated by means of cross-linking reaction, ATPase activity, salt solubility, and 40% saturated ammonium sulfate (AS) extractability. HRGS treatment of myofibrils caused cross-linking of myosin heavy chains (MHC) via disulfide bonding, an increase in Ca-ATPase activity, and a decrease in K-ATPase activity, suggesting that thiol groups of myosin including those at the active site were modified. The specific changes depended on the concentrations of H₂O ₂ in HRGS as well as the weight ratio of H₂O₂ to myofibrils. On the other hand, the decrease in salt solubility or AS extractability of myosin in HRGS-treated samples proceeded slowly when compared with the cross-linking reaction of MHC, indicating that considerable amounts of myosin biopolymers remained hydrophilic in the ionic solutions. The results demonstrated that initial cross-linking of MHC occurred inside the myosin molecule, and this was followed by progressive aggregation of myosin molecules through intermolecular cross-linking. Oxidation under the current experimental condition decreased the gel-forming ability of myofibrillar proteins, which coincided with the progress of the intra- and intermolecular cross-linking reactions as well as with ATPase activity changes.