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Updated: Apr 28, 2026

Expression, Purification, Crystallization, and Enzyme Assays of Fumarylacetoacetate Hydrolase Domain-Containing Proteins
Published on: June 20, 2019
Control of C4a-hydroperoxyflavin protonation in the oxygenase component of p-hydroxyphenylacetate-3-hydroxylase
Pirom Chenprakhon1, Duangthip Trisrivirat, Kittisak Thotsaporn
1Institute for Innovative Learning and ‡Department of Biochemistry and Center of Excellence in Protein Structure and Function, Faculty of Science, Mahidol University , Bangkok 10400, Thailand.
Abstract:
The protonation status of the peroxide moiety in C4a-(hydro)peroxyflavin of p-hydroxyphenylacetate-3-hydroxylase can be directly monitored using transient kinetics. The pKa for the wild-type (WT) enzyme is 9.8 ± 0.2, while the values for the H396N, H396V, and H396A variants are 9.3 ± 0.1, 7.3 ± 0.2, and 7.1 ± 0.2, respectively. The hydroxylation efficiency of these mutants is lower than that of the WT enzyme. Solvent kinetic isotope effect studies indicate that proton transfer is not the rate-limiting step in the formation of C4a-OOH. All data suggest that His396 may act as an instantaneous proton provider for the proton-coupled electron transfer that occurs before the transition state of C4a-OOH formation.
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