Abstract
We have developed a simple, reliable, and sensitive method for the assay of peroxisomal fatty acyl-CoA oxidase (FAO, EC 1.1.3-) in subcellular fractions. It is based on a peroxidase-linked oxidation of 4-hydroxyphenylacetic acid to a fluorescent compound [M.S. Poosch and R.K. Yamasaki (1986) Biochim. Biophys. Acta 884, 585–593]. Our method eliminates the contribution of important interfering side reactions, notably those due to the presence of reducing agents, which function as competitive substrates to 4-hydroxyphenylacetic acid. Rapidly reacting thiol groups are of particular importance, notably CoASH present endogenously (e.g. in peroxisomes and mitochondria) or formed by enzymatic hydrolysis of acyl-CoA. Alkylation of the thiol compounds by N-ethylmaleimide eliminates this disturbing side reaction, and increases the amount of fluorescent product in the coupled peroxidatic reaction. The method is suitable for routine assay of FAO activity in a wide range of tissues, notably in those with a low specific peroxisomal β-oxidation activity and/or a high content of reducing agents. As an example of this we have included data from rat heart peroxisomal fractions. The effct of alkylation of sulfhydryl groups in the incubation mixture also applies to other oxidase reactions based on H 2O 2-coupled peroxidatic reactions, if the oxidase itself does not contain functional sulfhydryl groups.
Published Version
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