A Spectrophotometric Method for the Determination of Aldehyde Oxidase Activity Using 3-Methyl-2Benzothiazolinone Hydrazine: A Preliminary Study

Aldehyde oxidase, a molybdenum cofactor-containing cytosolic enzyme, is extensively distributed throughout the animal kingdom. The enzyme is mainly active in liver and other tissues of mammalian species and involved in the metabolism of wide range of aldehydes and nitrogen-containing molecules. A continuous spectrophotometric method for the quantitative determination of aldehyde oxidase, AO, enzyme activity is described in this article. This method is based on the coupling reaction between 3-methyl-2-benzothiazolinone hydrazone (MBTH) and the o-quinone. Dopamine as substrate for AO, is converted/oxidized to o-quinone. The latter react with MBTH to produce intensely colored products that absorb light maximally in the visible region. Then, AO activity has been kinetically characterized; the Km (Michaelis–Menten constant) and Vmax (maximum initial velocity) values for the oxidation of dopamine by AO were evaluated. The existence of MBTH in the reaction medium and production of stable color as well as the high ϵ values at 510 nm of MBTH-Q adduct make this direct technique more sensitive than other continuous methods for AO assay. The optimized MBTH reaction may be useful for biological staining of AO activity isolated from various biological sources in electrophoresis gels.