Aromatic aldehydes as fluorogenic indicators for human aldehyde dehydrogenases and oxidases: substrate and isozyme specificity

Substrate properties of a number of potentially fluorogenic aromatic aldehy des of naphthalenes, phenanthrenes and anthracenes and of some coumarin ald ehydes towards various forms of the human and rat aldehyde oxidase and dehy drogenase were examined using absorption and emission spectroscopy. It was demonstrated that recombinant human class 1 aldehyde dehydrogenase (ALDH-1) readily oxidizes naphthalene (except for those ortho-substituted), phenant hrene and coumarin aldehydes, whereas the class 3 enzyme (ALDH-3) from huma n saliva is active only towards 2-naphthaldehyde derivatives. The observed reaction rates in both cases are comparable to those of the best known subs trates, and the K-m values are typically in the sub-micromolar range. Aldeh yde oxidases (AlOx), which are present in mammalian liver, reveal much broa der substrate specificity, oxidizing nearly all the compounds examined, inc luding those of the anthracene series, with maximum activity in the micromo lar range of substrate concentration. In rat liver, nearly all AlOx activit y was located in the cytosolic fraction.