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Superactivity and conformational changes on alpha-chymotrypsin upon interfacial binding to cationic micelles
M Soledad Celej1, Mariana G D'Andrea, Patricia T Campana
1Departamento de Química Biológica-CIQUIBIC, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba, Argentina.
The Biochemical Journal
|December 3, 2003
Summary
Alpha-chymotrypsin (alpha-CT) activity increases when interacting with cationic micelles of hexadecyltrimethylammonium bromide (CTABr). This enhanced catalytic efficiency is linked to significant conformational changes in the enzyme.
Area of Science:
- Biochemistry
- Enzyme kinetics
- Protein-micelle interactions
Background:
- Alpha-chymotrypsin (alpha-CT) is a key digestive enzyme.
- Cationic surfactants like hexadecyltrimethylammonium bromide (CTABr) can interact with enzymes.
- Understanding enzyme-surfactant interactions is crucial for enzyme engineering and applications.
Purpose of the Study:
- To investigate the effect of CTABr micelles on alpha-CT catalytic behavior and conformational changes.
- To determine how enzyme-micelle interactions influence enzyme kinetics and stability.
- To elucidate the structural basis for altered enzyme activity.
Main Methods:
- Enzyme kinetics assays using p-nitrophenyl acetate as substrate.
- Spectroscopic techniques: fluorescence spectroscopy, circular dichroism (CD) in near-UV and far-UV regions.
- Fourier-transform infrared (FTIR) spectroscopy.
Main Results:
- CTABr micelles significantly increased alpha-CT's V(max) and substrate affinity, enhancing catalytic efficiency.
- Enzyme stability remained largely unchanged in the presence of CTABr micelles.
- Conformational changes observed: increased tryptophan fluorescence intensity and red shift, altered aromatic residue environment, increased alpha-helical content, and decreased beta-sheet content.
Conclusions:
- The higher catalytic efficiency of micelle-bound alpha-CT is attributed to significant conformational alterations induced by CTABr micelles.
- These structural changes optimize the enzyme's active site for substrate interaction.
- The study highlights the potential of surfactant micelles as modulators of enzyme function.