Zymographic approach to determine the intrinsic enzyme specific activity of diamine oxidase in presence of interfering enzymes

Faster and sensitive zymographic detection of oxidases generating hydrogen peroxide. The case of diamine oxidase

The existing zymography method for the detection of diamine oxidase (DAO) activity has been improved by a new staining procedure with the aim to ameliorate its sensitivity. Both procedures used SDS-PAGE gels containing uniformly distributed entrapped peroxidase (that wouldn't migrate during electrophoresis). The new approach with 3,5-dichloro-2-hydroxybenzenesulfonate (DCHBS) as peroxidase substrate and with 4-amino-antipyrine as color stabilizer allows a more sensitive detection of DAO when compared to the previously reported o-phenylenediamine (o-PDA) as peroxidase substrate. The newly improved method appears faster, simple and environmentally friendly. It can be used for most of oxidases releasing hydrogen peroxide as reaction product.

In vitro determination of diamine oxidase activity in food matrices by an enzymatic assay coupled to UHPLC-FL

Intestinal diamine oxidase (DAO) acts as a protective barrier against exogenous histamine. A deficit of DAO activity can lead to the appearance of histamine intolerance, a clinical condition that may be treated by a low-histamine diet and oral DAO supplementation to enhance intestinal histamine degradation. As sources of DAO, porcine kidneys and certain legume seedlings are suitable components for the formulation of a DAO supplement. The aim of this work was to develop a rapid and reliable methodology for the in vitro determination of DAO activity in food matrices based on an enzymatic assay coupled to UHPLC-FL. The proposed method showed a satisfactory linearity and sensitivity and provided a relative standard deviation lower than 3%, guaranteeing method precision, and a mean recovery greater than 99% both for lyophilized pea sprouts and porcine kidney protein extracts. A high specificity is a key attribute of this method due to the use of histamine as the reaction substrate and the direct quantification of its degradation. Moreover, the lack of interference of catalase and hydrogen peroxide is another advantage in comparison with previously published methods. Lyophilized pea sprouts showed the greatest histamine-degrading activity (0.40 ± 0.01 mU/mg), followed by porcine kidney protein extracts (0.23 ± 0.01 mU/mg) and commercial DAO supplements (0.09 ± 0.06 mU/mg). This technique could be used as a tool to validate the DAO activity of food matrices of potential interest for the treatment of histamine intolerance.

Zymographic Determination of Intrinsic Specific Activity of Oxidases in the Presence of Interfering Proteins

Zymography on peroxidase-entrapped gels enables the determination of the intrinsic specific activity (ISA) of H₂O₂-producing oxidases in the presence of interfering enzymes including catalase (decomposing hydrogen peroxide). To reveal the searched oxidase, the zymography gel is incubated first in the developing solution containing the appropriate substrate of the oxidase and an oxidizable chromogen such as o-phenylenediamine (o-PDA) peroxidase substrate. The zymographic gel, after image analysis, can be restained by Coomassie Blue for molecular weights, for the whole electrophoretic pattern and for the protein concentration, thus allowing for the determination of oxidase ISA.