Related Experiment Video
Updated: Jun 7, 2026
Malachite Green Assay for the Discovery of Heat-Shock Protein 90 Inhibitors
Published on: January 20, 2023
An improved malachite green assay of phosphate: mechanism and application
1Unit for Biotransformation and Protein Biotechnology, Chongqing Key Laboratory of Biochemical and Molecular Pharmacology, Chongqing Medical University, Chongqing 400016, China.
Abstract:
The classical malachite green (MLG) assay of phosphate, which added MLG after molybdate to the acidified reaction solutions of phosphate, tolerated interference from papaverine, sildenafil, and some similar hydrophobic amines. Resonance Rayleigh scattering signals, the alleviation of interference by poly(vinyl alcohol), and the precipitation of some yellow complexes supported that the irreversible aggregation of the complexes of a hydrophobic amine of interference and phosphomolybdate reduced the amounts of phosphomolybdate accessible to MLG and caused the interference. By adding MLG before molybdate to the acidified reaction solutions of phosphate, the complexes of phosphomolybdate and MLG were preferentially formed before the complexes of phosphomolybdate and such a hydrophobic amine effectively aggregated; thereby, an improved MLG assay of phosphate with the resistance to common hydrophobic amines was developed. Using the improved MLG assay of phosphate and a phosphatase to release phosphate from AMP, a spectrometric method successfully estimated the half-inhibition concentrations of papaverine on the recombinant human cyclic nucleotide phosphodiesterase (PDE) isozyme 4 and the mixture of PDE isozymes from rabbit brain. Therefore, the improved MLG assay of phosphate was a favorable and universal technique for developing spectrometric methods for characterizing and screening inhibitors of enzymes that release phosphate during their actions.
Insights
An improved malachite green (MLG) assay for phosphate detection was developed by altering the order of reagent addition. This new method effectively minimizes interference from hydrophobic amines, enhancing phosphate analysis accuracy.
Area of Science:
- Analytical Chemistry
- Biochemistry
Background:
- The malachite green (MLG) assay is a common method for phosphate detection.
- Hydrophobic amines like papaverine and sildenafil can interfere with the classical MLG assay.
- This interference is attributed to the aggregation of phosphomolybdate complexes with hydrophobic amines, reducing MLG accessibility.
Purpose of the Study:
- To develop an improved malachite green (MLG) assay for phosphate detection that is resistant to interference from hydrophobic amines.
- To apply the enhanced assay for characterizing enzyme inhibitors.
Main Methods:
- The classical MLG assay involves adding MLG after molybdate to acidified phosphate solutions.
- The improved assay involves adding MLG before molybdate to acidified phosphate solutions.
- A phosphatase was used to release phosphate from AMP for inhibitor screening.
Main Results:
- The improved MLG assay demonstrated resistance to interference from common hydrophobic amines.
- The enhanced assay was successfully used to estimate the half-inhibition concentrations of papaverine on cyclic nucleotide phosphodiesterase (PDE) isozymes.
- Spectrometric methods were developed for characterizing and screening enzyme inhibitors.
Conclusions:
- The modified order of reagent addition in the MLG assay significantly improves its specificity.
- The improved MLG assay is a versatile technique for developing spectrometric methods for enzyme inhibitor characterization and screening.
- This method offers a favorable approach for biochemical assays involving phosphate release.
