Control of Activity through Oxidative Modification at the Conserved Residue Cys66 of Aryl Sulfotransferase IV

• Published in: The Journal of biological chemistry Vol. 272; no. 14; pp. 9153 - 9160
• Main Authors: Marshall, A. David, Darbyshire, John F., Hunter, Ann P., McPhie, Peter, Jakoby, William B.
• Format: Journal Article
• Language: English
• Published: American Society for Biochemistry and Molecular Biology 14.04.1997
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.272.14.9153

Oxidation at Cys 66 of rat liver aryl sulfotransferase IV alters the enzyme's catalytic activity, pH optima and substrate specificity. Although this is a cytosolic detoxication enzyme, the pH optimum for the standard assay substrate 4-nitrophenol is at pH 5.5; upon oxidation, the optimum changes to the physiological pH range. The principal effect of the change in pH optimum is activation, which is manifest by an increase in K ′ cat without any major influence on substrate binding. In contrast, with tyrosine methyl ester as a substrate, the enzyme's optimum activity occurs at pH 8.0; upon oxidation, it ceases to be a substrate at any pH. The presence of Cys 66 was essential for activation to occur, thereby providing a putative reason underlying the conserved nature of this cysteine throughout the phenol sulfotransferase family. Mapping of disulfides by mass spectrometry showed the critical event to be the oxidation of Cys 66 to form a disulfide with either Cys 232 or glutathione, either one is effective. These results point to a mechanism for regulating the activity of a key enzyme in xenobiotic detoxication during cellular oxidative stress.