An Improved Spectrophotometric Method for Toluene-4-Monooxygenase Activity

Area of Science:

• Biochemistry
• Enzyme Engineering
• Analytical Chemistry

Background:

• Monooxygenases are crucial enzymes with broad applications in biocatalysis.
• Existing colorimetric assays for monitoring monooxygenase activity lack quantitative accuracy due to unstable dye products.
• Distinguishing between regioisomeric products (e.g., 1-naphthol and 2-naphthol) typically requires complex chromatographic methods.

Purpose of the Study:

• To develop an improved, quantitative colorimetric assay for monooxygenase activity.
• To enable independent quantification of regioisomeric products without chromatographic separation.
• To provide a facile, low-cost, high-throughput method for enzyme activity monitoring.

Main Methods:

• Incorporation of an extraction step to stabilize and solubilize the colorimetric dye product.
• Application of spectral deconvolution techniques for distinguishing regioisomers.
• Validation of the improved assay using toluene-4-monooxygenase from Pseudomonas mendocina KR-1 and comparison with High-Performance Liquid Chromatography (HPLC).

Main Results:

• The improved assay enables stable, quantitative readout of enzyme activity.
• Independent quantification of 1-naphthol and 2-naphthol regioisomers is achieved for the first time using a colorimetric method.
• Results from the colorimetric assay show strong consistency with traditional HPLC analysis.

Conclusions:

• The developed quantitative colorimetric assay significantly advances analytical methods for monitoring monooxygenase activity.
• This assay offers a cost-effective and high-throughput alternative to chromatographic techniques for enzyme quantification.
• The method facilitates precise analysis of enzyme performance and product distribution, crucial for enzyme engineering applications.