Catalase-peroxidases in cyanobacteria--similarities and differences to ascorbate peroxidases

Area of Science:

• Biochemistry
• Enzymology
• Microbiology

Background:

• Cyanobacteria, or blue-green algae, are oxygenic phototrophic bacteria.
• Bifunctional catalase-peroxidases (CatPXs) are the primary hydrogen peroxide scavenging enzymes in some unicellular cyanobacteria.
• CatPXs share structural homology with plant ascorbate peroxidases (APXs).

Purpose of the Study:

• To investigate the optical and kinetic properties of CatPXs from Anacystis nidulans and Synechocystis PCC 6803.
• To compare the characteristics of cyanobacterial CatPXs with plant APXs.
• To elucidate the kinetic behavior and reaction mechanisms of CatPXs.

Main Methods:

• Spectroscopic analysis of ferric enzyme, Compound I, and cyanide complexes.
• Steady-state and transient-state kinetic studies.
• Measurement of bimolecular rate constants for Compound I formation and reduction.

Main Results:

• CatPXs and APXs exhibited similar spectra for the ferric enzyme, Compound I, and cyanide complex.
• CatPX Compound II spectra differed, resembling the native enzyme spectrum.
• Rate constants for Compound I formation with peroxoacetic acid were 5.9 x 10^4 M^-1 s^-1 (A. nidulans) and 8.7 x 10^3 M^-1 s^-1 (Synechocystis).
• The rate constant for Compound I reduction by ascorbate was significantly lower for CatPXs (5.4 x 10^3 M^-1 s^-1) compared to plant APXs.

Conclusions:

• Cyanobacterial CatPXs possess distinct kinetic properties, particularly in ascorbate reduction, compared to plant APXs.
• The high intrinsic catalase activity of CatPXs influences their reaction kinetics.
• These findings provide insights into the enzymatic mechanisms of oxidative stress response in cyanobacteria.