Journal article
Ionization of zwitterionic amine substrates bound to monomeric sarcosine oxidase
Biochemistry (Easton), Vol.44(51), pp.16866-16874
27 Dec 2005
PMCID: PMC2764489
PMID: 16363800
Featured in Collection : UN Sustainable Development Goals @ Drexel
Abstract
Monomeric sarcosine oxidase (MSOX) binds the L-proline zwitterion (pKa = 10.6). The reactive substrate anion is generated by ionization of the ES complex (pKa = 8.0). Tyr317 was mutated to Phe to determine whether this step might involve proton transfer to an active site base. The mutation does not eliminate the ionizable group in the ES complex (pKa = 8.9) but does cause a 20-fold decrease in the maximum rate of the reductive half-reaction. Kinetically determined Kd values for the ES complex formed with L-proline agree with results obtained in spectral titrations with the wild-type or mutant enzyme. Unlike the wild-type enzyme, Kd values with the mutant enzyme are pH-dependent, suggesting that the mutation has perturbed the pKa of a group that affects the Kd. As compared with the wild-type enzyme, an increase in charge transfer band energy is observed for mutant enzyme complexes with substrate analogues while a 10-fold decrease in the charge transfer band extinction coefficient is found for the complex with the L-proline anion. The results eliminate Tyr317 as a possible acceptor of the proton released upon substrate ionization. Since previous studies rule out the only other nearby base, we conclude that L-proline is the ionizable group in the ES complex and that amino acids are activated for oxidation upon binding to MSOX by stabilization of the reactive substrate anion. Tyr317 may play a role in substrate activation and optimizing binding, as judged by the effects of its mutation on the observed pKa, reaction rates, and charge transfer bands.
Metrics
1 Record Views
Details
- Title
- Ionization of zwitterionic amine substrates bound to monomeric sarcosine oxidase
- Creators
- Gouhua Zhao - Drexel UniversityMarilyn Schuman Jorns - Drexel University
- Publication Details
- Biochemistry (Easton), Vol.44(51), pp.16866-16874
- Publisher
- American Chemical Society; Washington, DC
- Grant note
- R01 GM031704 / NIGMS NIH HHS R01 GM031704-25 / NIGMS NIH HHS GM 31704 / NIGMS NIH HHS
- Resource Type
- Journal article
- Language
- English
- Academic Unit
- [Retired Faculty]
- Identifiers
- 991019168047204721
UN Sustainable Development Goals (SDGs)
This output has contributed to the advancement of the following goals:
InCites Highlights
These are selected metrics from InCites Benchmarking & Analytics tool, related to this output
- Web of Science research areas
- Biochemistry & Molecular Biology