l-Lysine effects on myosin carbonylation in metal-catalyzed oxidation: Implications for thermal gelation

This study investigated the impact of α-amino adipic semialdehyde (AAS)-mediated lysine carbonylation on the thermal gelation of porcine myosin. Purified myosin (2 mg/mL) was pre-treated with N-Ethylmaleimide to block the sulfhydryl groups, then oxidized in a metal-catalyzed oxidation system (10 μM FeCl₃, 100 μM ascorbic acid, and 5 mM H₂O₂) with varying l-lysine concentrations (0-60 mM) for 24 h at 4 °C. Physiochemical attributes, structural conformation, and rheological properties (G') of myosin were systematically monitored. Following heat-induced gelation (20-80 °C), the resulting gels were evaluated for water-holding capacity (WHC), microstructure, and intermolecular forces. Results showed that oxidation significantly induced myosin carboxylation, evidenced by a substantial increase in both total carbonyl and AAS contents. This oxidative stress triggered a decrease in protein solubility, increased turbidity and particle size, and the disruption of α-helix and tertiary structures. Consequently, the WHC and G' of the resulting gel declined markedly, characterized by a more porous and disordered microstructural network. Conversely, the addition of l-lysine effectively attenuated AAS formation in a dose-dependent manner, thereby mitigating the oxidative impairment of myosin's physiochemical and structural properties and preserving its gelation functionalities. These results indicate that AAS-mediated lysine carbonylation plays a detrimental role in myosin structural integrity and gelation performance. Furthermore, the incorporation of exogenous l-lysine offers a potential strategy to mitigate oxidative deterioration in muscle protein systems.