Aldehyde dehydrogenase in blood: a sensitive assay and inhibition by disulfiram.

The characteristics of human blood aldehyde dehydrogenase with indole-3-acetaldehyde as the substrate were investigated. Blood volumes of less than 25 microliter could be assayed. The Km-value was below 10 microM for indole-3-acetaldehyde and 100 microM for NAD+. The ALDH-activity appeared to be located exclusively in the intracellular fraction of the erythrocytes. Acetaldehyde or ethanol at concentrations up to 1 and 40 mM respectively did not affect the activity. Disulfiram caused a pronounced inhibition of the enzyme both in vitro and in vivo. The blood ALDH-activity in disulfiram-treated patients was not fully restored until 6 weeks after discontinuation of the treatment. The inhibition observed in vitro was reversed completely by 2-mercaptoethanol but only partially by glutathione. No restoration of activity in blood from disulfiram-treated patients was obtained with these two reagents. The inhibition found in vitro and in vivo was more pronounced when the assays were performed with indole-3-acetaldehyde than with acetaldehyde. The results suggest that different isozymes of ALDH are involved in the assay with these two substrates.