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Thiols as peroxidase substrates
B E Svensson1, A Gräslund, G Ström
1Department of Neuropharmacology, Astra Arcus AB, Södertälje, Sweden.
Free Radical Biology & Medicine
|February 1, 1993
Summary
Haem peroxidases catalyze thiol oxidation, with myeloperoxidase and eosinophil peroxidase showing distinct substrate preferences compared to lactoperoxidase and horseradish peroxidase. The thiolate anion is likely the key substrate in these reactions.
Area of Science:
- Biochemistry
- Enzymology
- Free Radical Chemistry
Background:
- Haem peroxidases are enzymes involved in various biological processes.
- Thiol compounds play crucial roles in cellular redox homeostasis and signaling.
- Understanding enzyme-substrate interactions is vital for elucidating biological functions.
Purpose of the Study:
- To investigate the catalytic oxidation of diverse thiols by different haem peroxidases.
- To characterize the substrate specificity of myeloperoxidase (MPO), eosinophil peroxidase (EPO), lactoperoxidase (LPO), and horseradish peroxidase (HRP).
- To explore the influence of pH on peroxidase-catalyzed thiol oxidation.
Main Methods:
- Spin-trapping electron spin resonance (ESR) spectroscopy was employed to detect and quantify radical intermediates.
- A panel of thiol compounds, including cysteamine, cysteine esters, 2-mercaptoethanol, thioglycollic acid, N-acetylcysteine, penicillamine, and glutathione, were used as substrates.
- Enzyme activity was assessed across varying pH conditions.
Main Results:
- Myeloperoxidase (MPO) and eosinophil peroxidase (EPO) effectively catalyzed the oxidation of cysteamine, cysteine methyl ester, and ethyl ester, with moderate activity towards 2-mercaptoethanol and thioglycolic acid.
- These leucocyte peroxidases exhibited poor catalytic activity against cysteine, N-acetylcysteine, penicillamine, and glutathione.
- Lactoperoxidase (LPO) and horseradish peroxidase (HRP) demonstrated different substrate specificities compared to MPO and EPO.
- pH-dependence studies suggested that the thiolate anion is the active substrate for peroxidase-catalyzed thiol oxidation.
Conclusions:
- Leukocyte haem peroxidases (MPO and EPO) exhibit specific substrate preferences for thiol oxidation.
- Distinct catalytic profiles exist among different classes of haem peroxidases regarding thiol substrates.
- The findings highlight the role of the thiolate anion in peroxidase-mediated thiol oxidation and suggest implications for cellular redox processes.