An improved spectrophotometric assay for histamine and diamine oxidase (DAO) activity

Diamine oxidase or its substrates can be measured using a coupled reaction with peroxidase and the chromogen 3-methyl-2-benzothiazolone hydrazone (MBTH) with an appropriate acceptor such as 3-(dimethylamino)benzoic acid (DMAB). This method provides a more rapid and sensitive method of measuring histamine than current colorimetric assays; using this system, histamine was quantitated at concentrations of 10 to 400 mumol/l. The Km of DAO was determined to be 2.9 X 10(-5) M, a lower value than previously reported.