Hydroxyl Radical-Induced Oxidation on the Properties of Cathepsin H and Its Influence in Myofibrillar Proteins Degradation of Coregonus peled In Vitro .

The most frequently occurring protein modification in fish postmortem is oxidization, which further affects meat quality through multiple biochemical pathways. To investigate how hydroxyl radicals affect the structure of cathepsin H and its ability to break down myofibrillar proteins in Coregonus peled , cathepsin H was oxidized with 0, 0.1, 0.5, 1, 5, and 10 mM H 2 O 2 and subsequently incubated with isolated myofibrillar proteins. The results showed that as the H 2 O 2 concentration increased, the carbonyl and sulfhydryl contents of cathepsin H significantly increased and decreased, respectively. There were noticeable changes in the α-helix structures and a gradual reduction in UV absorbance and fluorescence intensity, indicating that oxidation can induce the cross-linking and aggregation of cathepsin H. These structural changes further reduced the activity of cathepsin H, reaching its lowest at 10 mM H 2 O 2 , which was 53.63% of the activity at 0 mM H 2 O 2 . Moreover, desmin and troponin-T all degraded at faster rates when cathepsin H and myofibrillar proteins were oxidized concurrently as opposed to when cathepsin H was oxidized alone. These findings provide vital insights into the interaction mechanism between oxidation, cathepsin H, as well as myofibrillar protein degradation, laying a groundwork for understanding the molecular mechanisms underlying changes in fish meat quality after slaughter and during processing.