Aldehyde reductase from Crithidia fasciculata: purification and characterization.

Crithidia fasciculata, a pterin requiring protozoa, contained a NADPH-dependent dihydro-6-formylpterin reducing enzyme. The aldehyde reductase was purified and characterized. This enzyme was soluble and constitutive, and had the ability to catalyze the interconversion between aldehydes and alcohols. The optimal pH was 7.0 for the reductase activity and 9.0 for the dehydrogenase activity. The enzyme had a broad substrate specificity and reduced aromatic and aliphatic aldehydes such as dihydro-6-formylpterin, benzaldehyde, pyridine-3-aldehyde, butyraldehyde, DL-glyceraldehyde, and acetaldehyde. The enzyme was inhibited by sulfhydryl reagents and heavy metals, but not inhibited by chelating reagents. Its molecular weight was determined to be 66,000 and 72,000 by gel filtration and sedimentation equilibrium analysis, respectively. The value of 39,000 was obtained by sodium dodecyl sulfate gel electrophoresis indicating a dimeric structure. The aldehyde reductase of Crithidia may be classified as NADP+-dependent aryl-alcohol dehydrogenase [EC 1.1.1.91].