[Chemical modification of lysine epsilon-NH2-groups in horseradish peroxidase. Its effect on enzyme stability. Temperature dependence of thermo-inactivation constants for native and modified peroxidase].

Summary

# Editorial Summary Researchers chemically modified horseradish peroxidase—an enzyme used as a model system for understanding protein stability—by altering lysine residues with various chemical agents, then tested how these changes affected the enzyme's ability to withstand heat between 56–80°C. Modifying four amino groups via acylation or three groups via arylation actually improved thermal stability, whilst modification of six groups reduced it, demonstrating that selective chemical alteration can either strengthen or weaken enzyme resilience depending on the degree and type of modification applied. The native enzyme showed a heat-inactivation enthalpy of 30±1 kcal/mol, whereas chemically modified versions displayed substantially higher values (64–87 kcal/mol), indicating that modified enzymes required greater energy input before they began to denature irreversibly. Whilst this foundational biochemistry work used a plant enzyme rather than equine tissue, the principles underlying protein stability under thermal stress are directly relevant to understanding how heat affects performance-critical proteins in horses—particularly during intense exercise or fever—and may inform future strategies for stabilising therapeutic or nutritional proteins used in equine practice.

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Key Findings

• •Chemical modification of 4 lysine amino groups via acylation and 3 groups via TNBS arylation stabilized horseradish peroxidase enzyme
• •Modification of 6 amino groups decreased enzyme stability across 56-80°C temperature range
• •Modified peroxidase showed increased thermodynamic activation parameters (ΔH 64-87 kcal/mole vs 30±1 for native; ΔS 110-178 vs 14 for native)
• •Chemical modification did not alter pH-dependent thermostability profile of the enzyme