Pirom Chenprakhonภิรมย์ เชนประโคนDuangthip TrisriviratKittisak ThotsapornJeerus SucharitakulPimchai ChaiyenMahidol University. Institute for Innovative LearningMahidol University. Faculty of ScienceChulalongkorn University. Faculty of Dentistry2015-08-032018-01-262015-08-032018-01-262014-07Biochemistry. Vol.53, (2014), 4084-4086https://repository.li.mahidol.ac.th/handle/20.500.14594/3395The protonation status of the peroxide moiety in C4a-(hydro)peroxyflavin of p-hydroxyphenyla- cetate-3-hydroxylase can be directly monitored using transient kinetics. The p K a 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 e ffi ciency of these mutants is lower than that of the WT enzyme. Solvent kinetic isotope e ff ect 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.engMahidol UniversityArticleAmerican Chemical Society10.1021/bi500480n