Betaine aldehyde dehydrogenase (BADH) activity might be crucial for the growth of the human pathogen Pseudomonas aeruginosa under conditions of
infection and therefore appears to be a suitable target for
antimicrobial agents. As a first step in the search for BADH inhibitors, we have tested the effects of the known
aldehyde dehydrogenase inhibitor
disulfiram (DSF) on the activity of P. aeruginosa and Amaranthus hypochondriacus (amaranth) leaf BADHs. DSF totally inactivated both
enzymes in a time- and dose-dependent manner. In the case of the Pseudomonas
enzyme, inactivation kinetics were monophasic with a second-order inactivation rate constant at pH 6.9 of 4.9+/-0.4 M(-1) s(-1), whereas the plant
enzyme was inactivated in a biphasic process with second-order inactivation rate constants at pH 7.5 of 6.8+/-0.6 and 0.33+/-0.04 M(-1) s(-1). At pH 8.8, the second-order rate constants for inactivation of the bacterial
enzyme was 1 x 10(3) M(-1) s(-1), which compare well with that reported for human liver
mitochondrial aldehyde dehydrogenase (ALDH2), the target of DSF inhibition in the aversion therapy of
alcoholism. Both BADHs were inactivated faster in the presence of
NAD(P)(+) than in its absence, whereas
NAD(P)H and
betaine aldehyde protected the bacterial, but increased the inactivation rate of the plant
enzyme. The inactivated
enzymes were reactivated by
dithiothreitol, but not by a high concentration of the physiological
reductant glutathione. The high in vitro sensitivity of the Pseudomonas BADH to DSF, particularly in the presence of
NAD(P)(+), together with the lack of reversibility of DSF modification by
glutathione, makes this inhibitor a potential
antimicrobial agent and suggests that it might be worth testing its effects and those of its metabolites in vivo, under culture conditions in which the activity of BADH is required for growth of the bacteria.