Inhibition of human aldehyde dehydrogenase isozymes by propiolaldehyde

Propiolaldehyde--a metabolite of pargyline (Shirota et al., 1979) can function as an inhibitor or as a substrate of human aldehyde dehydrogenase (EC 1.2.1.3), dependent on conditions. In the presence of high concentration of NAD, propiolaldehyde is a substrate for both the cytoplasmic E1 isozyme and the mitochondrial E2 isozyme. The Km values are comparable to those with other short chain aldehydes; the maximal velocity is also similar for E2 but lower by about three-fold for E1. Preincubation with propiolaldehyde in the absence of NAD produces inactivation with K1 values of 1.6 microM for E1 and 1.8 microM for E2. NAD, but not propanal, protects both isozymes against inactivation with propiolaldehyde.