Investigation of the sulfuryl transfer step from substrate to enzyme by arylsulfatases

The reactions of the arylsulfatase A (ASA) from Helix pomatia and that from Aerobacter aerogenes with p‐nitrophenyl sulfate were examined by determination of the pH dependence of Vmax/Km and by measurement of kinetic isotope effects. Both enzymes exhibit bell‐shaped pH–rate dependences for Vmax/Km....

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Bibliographic Details
Published in:Journal of physical organic chemistry 2004-06, Vol.17 (6-7), p.541-547
Main Authors: Gibby, Stuart G., Younker, Jarod M., Hengge, Alvan C.
Format: Article
Language:English
Subjects:
arylsulfatase
catalytic mechanism
isotope effect
sulfuryl transfer
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Summary:The reactions of the arylsulfatase A (ASA) from Helix pomatia and that from Aerobacter aerogenes with p‐nitrophenyl sulfate were examined by determination of the pH dependence of Vmax/Km and by measurement of kinetic isotope effects. Both enzymes exhibit bell‐shaped pH–rate dependences for Vmax/Km. The ASA from Helix pomatia exhibits a more acidic pH optimum (pH 4–5) than the ASA from Aerobacter aerogenes (pH ∼7). The sulfuryl transfer from substrate to enzyme is general acid‐assisted in both enzymes, but isotope effects indicate differences in the synchronicity of protonation with SO bond fission. In the reaction of the Helix pomatia enzyme, protonation is synchronous with bond fission and the leaving group is fully neutralized in the transition state. In the reaction catalyzed by the Aerobacter aerogenes ASA, protonation of the leaving group lags behind bond fission and the leaving group bears a partial negative charge in the transition state. Copyright © 2004 John Wiley & Sons, Ltd.
ISSN:0894-3230
1099-1395
DOI:10.1002/poc.775