Chlorinated acetaldehydes have been
the focus of research due to their role as reactive intermediates and their possible occurrence in chlorinated drinking water. This study investigated the in vitro substrate specificity of cytosolic and mitochondrial rat liver aldehyde dehydrogenase toward these compounds. Monochloroacetaldehyde was found to be extensively metabolized by these enzymes, to an even greater extent than the standard substrate propionaldehyde. Dichloroacetaldehyde was metabolized to a much lesser extent, and chloral hydrate is not metabolized by this enzyme family. The K, (mM) and V, , (Vmm for propionaldehyde set to 100) values with the low K, cytosolic enzyme were monochloroacetaldehyde 0.046 and 582, and dichloroacetaldehyde 0.13 and 54.9, and those with the high K,,, cytosolic enzyme were dichloroacetaldehyde 0.35 and 23.4. The values with the low K, mitochondrial enzyme were monochloroacetaldehyde 0.057 and 462 and dichloroacetaldehyde 0.038 and 12.9, and those with the high K , mitochondrial enzyme were monochloroacetaldehyde 0.024 and 55.5 and dichloroacetaldehyde 0.29 and 3.44. These data suggest that aldehyde dehydrogenase plays a significant role in the metabolism of monochloroacetaldehyde and, to some extent, dichloroacetaldehyde. Some evidence also suggested that alcohol dehydrogenase plays a significant role in the metabolism of dichloroacetaldehyde and chloral hydrate.