A simple and continuous assay for decarboxylase activity using a carbon dioxide-selective electrode

Assays for amino acid decarboxylase enzymes using ion-exchange cartridges

A general radiochemical method for estimating the activity of amino acid decarboxylases is reported. This method utilizes ion-exchange cartridges to separate unreacted radiolabeled amino acid substrates from product amines, which can then readily be quantitated by liquid scintillation counting. The assay is simple, rapid, and more sensitive than standard 14CO2 trapping procedures if uniformly labeled amino acid substrates are utilized. Acidic, basic, and aromatic amino acid decarboxylases can be assayed with the appropriate choice of cation or anion exchangers. The utility of the method is demonstrated for aspartate-alpha-decarboxylase, tyrosine decarboxylase, and lysine decarboxylase where kinetic parameters are comparable to values obtained by standard radiochemical 14CO2 trapping assays.

Assay for aliphatic amino acid decarboxylases by high-performance liquid chromatography

A sensitive and rapid assay for aliphatic amino acid decarboxylases based on separation of the product from the substrate by ion-pairing reversed-phase high-performance liquid chromatography and subsequent fluorometric detection has been developed. The resolution of substrates and products of seven amino acid decarboxylases, namely, arginine, aspartate, 2,6-diaminopimelate, histidine, glutamate, lysine, and ornithine decarboxylase, is complete within 15 to 35 min of isocratic elution. The limit of detection for the product is 40 pmol. The applicability of the procedure was assessed with glutamate decarboxylase. The formation of the product 4-aminobutyrate proved to be linear with time and protein concentration. The method allows the time course of the reaction to be followed in a single assay and works well with crude extracts of bacteria or tissues.

A continual spectrophotometric assay for amino acid decarboxylases

A spectrophotometric method for assaying the activity of three amino acid decarboxylases is reported. This method makes use of the coupled reaction of the decarboxylase with phosphoenolpyruvate carboxylase and malate dehydrogenase. The assay is simple and rapid and allows continuous monitoring of the reaction progress. The kinetic parameters obtained using this method for diaminopimelate decarboxylase, lysine decarboxylase, and arginine decarboxylase are comparable to values obtained by radiochemical methods.

Lysine decarboxylase assay by the pH-stat method

A simple assay of lysine decarboxylase is described. It is based on measuring the rate of titration of OH- ions, released during decarboxylation with the aid of a pH-stat apparatus. The continuous recording of the reaction progress may be easily performed. Using the pH-stat method the Km for lysine decarboxylase from E. coli is 2.0 mM.

Oxygraphic assay of 3,4-dihydroxyphenylalanine decarboxylase activity by coupled reaction with free and immobilized serum amine oxidase

An oxygraphic method for the assay of 3,4-dihydroxyphenylalanine (Dopa) decarboxylase activity which makes use of the coupled reactions of Dopa decarboxylase with serum amine oxidase is presented. Both free and immobilized amine oxidases were utilized. The assay is simple, rapid, and allows a continuous monitoring of the reaction. The kinetic parameters for Dopa decarboxylase obtained with the coupled assay do not significantly differ from those obtained by standard methods.