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Updated: Sep 25, 2025
A Mass Spectrometry-Based Approach to Identify Phosphoprotein Phosphatases and their Interactors
Published on: April 29, 2022
Assessing the microcystins concentration through optimized protein phosphatase inhibition assay in environmental
Kyoung-Hee Oh1, Kung-Min Beak1, Yuna Shin2
1Department of Environmental Engineering, Chungbuk National University, Cheongju, 28644, Republic of Korea.
Abstract:
Protein phosphatase (PPase) inhibition assay (PPIA) is widely used to analyze the concentration of microcystins (MCs) because it is comparatively less expensive and faster than other assays. This study aimed to optimize the PPIA by determining a suitable reaction terminator and an optimal methanol concentration in the sample. The most suitable reaction time was 90 min, with the corresponding methanol concentration in the sample being 15% or less. When p-nitrophenyl phosphate (pNPP) was used as a substrate, copper chloride solution was suitably used as a reaction terminator, and when 4-methylumbelliferyl phosphate (MUP) was used, a glycine buffer not only increased the measurement sensitivity of the reaction product but also terminated the enzymatic reaction. When PPase 1 and MUP were used as an enzyme and a substrate, respectively, the limit of quantitation for MC-leucine/arginine (LR) was 0.02 µg/L, whereas it was 0.1 µg/L when pNPP was used as a substrate. The proposed method facilitated the measurement of MC-LR concentration without additional pretreatments, such as concentration or purification; therefore, this method was suitable and feasible for the continuous monitoring of MCs in drinking water.
Insights
Optimizing the protein phosphatase inhibition assay (PPIA) for microcystin (MC) detection involves finding the best reaction terminator and methanol concentration. This enhanced method allows for continuous monitoring of MCs in drinking water.
Area of Science:
- Environmental Chemistry
- Analytical Chemistry
- Biochemistry
Background:
- Protein phosphatase inhibition assay (PPIA) is a common method for quantifying microcystins (MCs).
- Optimization is needed to improve the assay's sensitivity and applicability for real-world samples.
- Current methods may require extensive sample pretreatment.
Purpose of the Study:
- To optimize the PPIA by identifying optimal reaction terminators and methanol concentrations.
- To establish a sensitive and feasible method for continuous microcystin monitoring in drinking water.
Main Methods:
- Investigated various reaction terminators (copper chloride, glycine buffer) for PPIA.
- Determined optimal methanol concentrations and reaction times (90 min).
- Compared assay performance using different substrates (p-nitrophenyl phosphate - pNPP, 4-methylumbelliferyl phosphate - MUP) and enzyme (PPase 1).
Main Results:
- Glycine buffer enhanced sensitivity and terminated the reaction when MUP was used as a substrate.
- Copper chloride was a suitable terminator when pNPP was used.
- The optimized method achieved a limit of quantitation of 0.02 µg/L for MC-leucine/arginine (LR) using PPase 1 and MUP.
- Methanol concentration of 15% or less was optimal.
Conclusions:
- The optimized PPIA method allows for direct measurement of MC-LR without pretreatment.
- This method is suitable and feasible for continuous monitoring of microcystins in drinking water.
- The study provides a refined protocol for sensitive and efficient MC analysis.
