Redox control of aryl sulfotransferase specificity

Area of Science:

• Biochemistry
• Enzymology
• Drug Metabolism

Background:

• Aryl sulfotransferase IV (AS IV) is a rat liver enzyme involved in detoxification.
• Its activity is typically optimal at pH 5.5, showing low efficacy at physiological pH.
• This pH-dependent activity suggested limited physiological relevance for the enzyme.

Purpose of the Study:

• To investigate the effect of the enzyme's redox state on its activity and substrate specificity.
• To elucidate the mechanism by which redox changes influence AS IV function.
• To understand how these changes impact enzyme-substrate and enzyme-product interactions.

Main Methods:

• Enzyme assays using conventional substrates like 4-nitrophenol and PAPS.
• Investigating enzyme activity under varying pH conditions and redox states (reduced vs. partially oxidized).
• Analysis of ternary complex formation and its impact on enzyme kinetics and substrate binding.

Main Results:

• Partial oxidation of AS IV significantly increased sulfation rates at physiological pH.
• Oxidation shifted the pH optimum to the physiological range and altered substrate specificity.
• The redox state controls enzyme activity by modulating ternary complex formation, preventing product inhibition in the oxidized state.

Conclusions:

• The redox state of AS IV acts as a molecular switch, regulating its catalytic efficiency.
• Oxidation at Cys66 is crucial for activating the enzyme at physiological pH.
• Understanding this redox regulation is key to understanding the physiological role of AS IV in detoxification pathways.