Functional and structural analysis of catalase oxidized by singlet oxygen

Area of Science:

• Biochemistry
• Enzymology
• Oxidative Stress Biology

Background:

• Catalase-1 (CAT-1) from Neurospora crassa is crucial for managing reactive oxygen species.
• Singlet oxygen is known to oxidize CAT-1, altering its properties.
• Understanding these modifications is key to cellular defense mechanisms.

Purpose of the Study:

• To compare the functional and structural characteristics of non-oxidized and singlet oxygen-oxidized CAT-1.
• To investigate the kinetic properties and stability of both enzyme forms.
• To elucidate the implications of CAT-1 oxidation under physiological conditions.

Main Methods:

• Enzyme kinetics analysis across a broad hydrogen peroxide concentration range.
• Spectroscopic methods (protein fluorescence, circular dichroism) for structural assessment.
• Stability assays under varying temperature, pH, and chemical denaturant conditions.

Main Results:

• Non-hyperbolic saturation kinetics observed in both enzyme forms, suggesting complex active sites.
• Minimal gross conformational changes detected via fluorescence and circular dichroism.
• Oxidized CAT-1 exhibited increased cyanide sensitivity and reduced stability to heat, guanidinium ions, and acidic pH.
• Despite alterations, oxidized CAT-1 maintained significant catalytic efficiency and stability.

Conclusions:

• Heme oxidation by singlet oxygen induces local active site changes and affects overall stability, but not gross structure.
• Catalase-1's ability to retain function after oxidation is vital for cellular survival during oxidative stress.
• Evolutionary selection likely favored these properties to ensure enzyme activity under challenging physiological conditions.