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Related Experiment Video

Updated: Apr 23, 2026

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Novel reference method for precise determination of tryptophanase activity.

Marwa M Ali1, Inas J Mahdi1, Hayder Obayes Hashim2

  • 1Chemistry Department, College of Science, University of Babylon, Hilla City, Babylon Governorate 51001, Iraq.

Biology Methods & Protocols
|April 22, 2026
PubMed
Summary
This summary is machine-generated.

A new spectrophotometric assay using 2,4-dinitrophenylhydrazine (2,4-DNPH) offers a simple, cost-effective method for measuring tryptophanase (TnaA) activity. This validated assay is comparable to existing methods and suitable for routine diagnostics and research.

Keywords:
2,4-dinitrophenylhydrazineEscherichia coliHPLCKovács reagentpyruvatetryptophanase

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Area of Science:

  • Biochemistry
  • Enzymology
  • Analytical Chemistry

Background:

  • Tryptophanase (TnaA) is crucial for bacterial signaling, biofilm formation, and L-tryptophan biosynthesis.
  • Current TnaA activity assays (Kovács, HPLC, NADH-coupled) have limitations in cost, complexity, or sensitivity.
  • A need exists for a simpler, more accessible method for routine TnaA quantification.

Purpose of the Study:

  • To develop and validate a cost-effective spectrophotometric assay for TnaA activity using 2,4-dinitrophenylhydrazine (2,4-DNPH).
  • To target the pyruvate product of the TnaA enzymatic reaction for quantification.
  • To assess the assay's performance and compare it with established methods.

Main Methods:

  • A spectrophotometric assay was developed using 2,4-DNPH to detect pyruvate, the product of TnaA-catalyzed L-tryptophan degradation.
  • The assay was applied to Escherichia coli lysates and validated for linearity, detection limits, precision, and selectivity.
  • Method comparison involved Kovács colorimetry and HPLC using Passing-Bablok and Bland-Altman analyses.

Main Results:

  • The DNPH-TnaA assay demonstrated good linearity (5-500 µM) with low limits of detection (2.25 U/l) and quantification (6.7 U/l).
  • High precision was observed with intra-assay CV of 1.19% and inter-assay CV of 2.65%.
  • The assay showed excellent agreement with Kovács and HPLC methods, indicating comparable accuracy and robustness.

Conclusions:

  • The developed DNPH-TnaA assay is a precise, accurate, and robust method for quantifying TnaA activity.
  • Its simplicity, low cost, and compatibility with standard laboratory equipment make it ideal for routine use.
  • This assay provides a valuable alternative for TnaA activity measurement in diagnostic and research settings.