Oxidation desensitizes actomyosin to magnesium pyrophosphate-induced dissociation

• Hydroxyl radical destabilizes myosin head.
• Oxidation weakens the binding of pyrophosphate-Mg2+ to myosin.
• Oxidation desensitizes actomyosin to pyrophosphate.
• Oxidation inhibits the dissociation of actomyosin by pyrophosphate.

This study aimed to establish the influence of protein oxidation on the ability of magnesium pyrophosphate (PP) to dissociate actomyosin. Actomyosin isolated from pork muscle then suspended in 0.1 M NaCl at pH 6.2 was oxidatively stressed with 10 μM FeCl3/0.1 mM ascorbate/1 mM H2O2 for 6 or 12 h at 4 °C. Protein oxidation was evidenced by the loss of myosin and actin, the concomitant formation of disulphide-cross-linked polymers, and elevated myosin ATPase activity. The intrinsic viscosity of oxidized actomyosin had a weaker response to PP-Mg2+ than that of non-oxidized actomyosin, indicating the suppression of actomyosin dissociation. Moreover, oxidized actomyosin solutions were devoid of small particles (<10 nm) and the stressed actomyosin exhibited weaker binding of PP-Mg2+ than non-oxidized, which further suggested a reduced myosin–PP interaction and subsequent dissociation of the actomyosin complexes.