Non-chemical proton-dependent steps prior to O2-activation limit Azotobacter vinelandii 3-mercaptopropionic acid dioxygenase (MDO) catalysis
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- 作者：Joshua K. Crowell ; Sinjinee Sardar ; Mohammad S. Hossain ; Frank W. Foss Jr. ; Brad S. Pierce ; bspierce@uta.edu" class="auth_mail" title="E-mail the corresponding author
- 关键词：Non-heme mononuclear iron ; Thiol dioxygenase ; Solvent isotope effects ; Proton inventory ; Viscosity effects
- 刊名：Archives of Biochemistry and Biophysics
- 出版年：2016
- 出版时间：15 August 2016
- 年：2016
- 卷：604
- 期：Complete
- 页码：86-94
- 全文大小：913 K
文摘
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The pH-dependent kinetics of Av MDO can be fit assuming a diprotic model where three ionic forms of the enzyme are present.
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A normal solvent isotope effect of 2.7 ± 0.4 is observed in 3mpakcat/KM-data indicating non-chemical steps are limiting.
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Within pL-independent regions, proton-inventory of 3mpakcat/KM-results is best fit assuming a single proton in flight.
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Two catalytically relevant pKa-values are identified; tentatively, assigned to residues within the MDO catalytic triad.
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Solvent viscosity experiments demonstrate that diffusional steps are not rate limiting for 3mpa or cys reactions.