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Enzymatic catalysis and dynamics in low-water environments.
1Department of Chemical Engineering, University of California, Berkeley 94720.
Summary
Adding small amounts of water to enzymes in organic solvents enhances their activity by increasing flexibility. However, too much water decreases enzyme transesterification activity, suggesting a specific hydration level is optimal for enzyme function.
Area of Science:
- Biochemistry
- Enzyme kinetics
- Biophysical chemistry
Background:
- Enzymes in organic solvents are crucial for biocatalysis and studying enzyme mechanisms.
- The role of water in enzyme structure and function, especially in non-aqueous media, remains an active area of research.
Purpose of the Study:
- To investigate the effect of varying water content on the transesterification activity of subtilisin Carlsberg in organic solvents.
- To correlate changes in enzyme activity with alterations in active-site polarity and enzyme mobility.
Main Methods:
- Enzyme activity assays (transesterification) were performed on subtilisin Carlsberg in tetrahydrofuran with 1-propanol.
- Nitroxide spin labeling was used to monitor changes in active-site polarity and mobility as a function of water content.
- Enzyme hydration levels were controlled and quantified.
Main Results:
- Subtilisin Carlsberg activity significantly increased with the addition of <1% water, correlating with increased active-site polarity and mobility.
- Activity decreased dramatically with water content >1%, despite further increases in mobility.
- A distinct optimal hydration range was identified for maximal transesterification activity.
Conclusions:
- Enzyme hydration and flexibility are critical factors influencing enzyme activity in organic solvents.
- Partially hydrated subtilisin exhibits a different conformation compared to nearly dry or highly hydrated states.
- These findings highlight the delicate balance of water required for optimal enzyme performance in non-aqueous environments.