Selective assay of the cytosolic forms of the aldehyde dehydrogenase in rat, with possible significance for the investigations of cyclophosphamide cytotoxicity.

Continuous fluorimetric assay for aldehyde dehydrogenase activity in rat tissue, based on oxidation of the fluorogenic 6-methoxy-2-naphthaldehyde, is described. The new assay is ca. 2 orders of magnitude more sensitive than the standard procedures and it is not subjected to interferences by other dehydrogenases, although occasionally the aldehyde dehydrogenase activity may be obscured by aldehyde oxidase. The new fluorimetric assay is highly selective for the cytosolic forms of the both rat and human aldehyde dehydrogenase, which are primarily responsible for cyclophosphamide inactivation in vivo. These forms can now be detected in crude homogenates of several rat organs without necessity of subcelluar fractionation.