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Continuous spectrometric assays for glutaminyl cyclase activity
Stephan Schilling1, Torsten Hoffmann, Michael Wermann
1Laboratory of Biochemistry, probiodrug AG, Weinbergweg 22, 06120 Halle/Saale, Germany.
Analytical Biochemistry
|March 22, 2002
Summary
A new coupled assay was developed to measure glutaminyl cyclase (QC) activity using pyroglutamyl aminopeptidase. This method accurately quantifies QC enzyme kinetics, even with ammonium ions present.
Area of Science:
- Biochemistry
- Enzymology
Background:
- Glutaminyl cyclase (QC) plays a crucial role in enzymatic conversions.
- Existing methods for QC activity estimation have limitations, especially in the presence of ammonium ions.
Purpose of the Study:
- To develop a novel, reliable assay for quantifying glutaminyl cyclase (QC) activity.
- To characterize the kinetic parameters of purified papaya QC using chromogenic and fluorogenic substrates.
- To assess the assay's performance in the presence of varying ammonia and ionic strength concentrations.
Main Methods:
- A coupled assay was designed utilizing pyroglutamyl aminopeptidase as an auxiliary enzyme.
- The assay measures the conversion of l-glutamine-p-nitroanilide, l-glutaminyl-2-naphthylamide, and l-glutaminyl-4-methylcoumarinylamide by QC.
- Kinetic parameters were determined for purified papaya QC.
Main Results:
- The new assay accurately estimates QC activity using both chromogenic and fluorogenic substrates.
- Kinetic parameters for purified papaya QC align with previously reported values for other glutaminyl peptides.
- The assay is robust, functioning effectively with ammonia concentrations up to 50 mM and showing increased activity with ionic strength up to 300 mM KCl.
Conclusions:
- This study presents the first fast, continuous, and reliable method for determining glutaminyl cyclase activity.
- The assay is suitable for use during protein purification and enzymatic analysis, even in the presence of ammonium ions.