Studies on the interaction between disulfiram and sheep liver cytoplasmic aldehyde dehydrogenase

Abstract

The effect of disulfiram, [1-14C]disulfiram and some other thiol reagents on the activity of cytoplasmic aldehyde dehydrogenase from sheep liver was studied. The results are consistent with a rapid covalent interaction between disulfiram and the enzyme, and inconsistent with the notion that disulfiram is a reversible competitive inhibitor of cytoplasmic aldehyde dehydrogenase. There is a non-linear relationship between loss of about 90% of the enzyme activity and amount of disulfiram added; possible reasons for this are discussed. The remaining approx. 10% of activity is relatively insensitive to disulfiram. It is found that modification of only a small number of groups (one to two) per tetrameric enzyme molecule is responsible for the observed loss of activity. The dehydrogenase activity of the enzyme is affected more severely by disulfiram than is the esterase activity. Negatively charged thiol reagents have little or no effect on cytoplasmic aldehyde dehydrogenase. 2,2'-Dithiodipyridine is an activator of the enzyme.

Reversal of part of the aldehyde dehydrogenase reaction pathway during the hydrolysis of an ester

“…1 shows that for the present preparation of aldehyde dehydrogenase a well-known enzyme inhibitor, iodoacetamide, produces similar inhibition of the aldehyde dehydrogenase, steroid-sensitive aldehyde dehydrogenase and esterase activities of the preparation. Such inhibition is consistent with all these reactions being catalysed by the active sites of the same enzyme, but is apparently distinct from the inhibition of a preparation of cytosolic aldehyde dehydrogenase from sheep liver, whose esterase activity is more resistant to inhibition by disulfiram than is the dehydrogenase activity (Kitson, 1978).…”

“…The data of Nousiainen et al (1978) do not rule out the existence of aldehyde dehydrogenase and 4-nitrophenyl esterase activities on the same protein; an equally valid explanation is that there is more than one type of esterase, with most of the activity not being contributed by the phenobarbital-inducible aldehyde dehydrogenase. The data of Kitson (1978), showing sheep liver aldehyde dehydrogenase and esterase being differentially inhibited by disulfiram, may have to be reassessed in view of the report by Dickinson & Berrieman (1979) of the difficulty of separation of cytosolic and mitochondrial aldehyde dehydrogenases in that species, and the resistance of the mitochondrial enzyme to inhibition by disulfiram. If most of the esterase activity of the enzyme preparation studied by Kitson (1978) is provided by contaminating mitochondrial disulfiram-resistant aldehyde dehydrogenase the apparent differential inhibition of the two activities simply reflects the different dehydrogenase/esterase activity ratios of the two isoenzymes.…”

“…Also, as reported by Hart & Dickinson (1978), acetic anhydride (which is presumed to acetylate the enzyme to give an intermediate similar to that postulated in ester hydrolysis) may be partially reduced to an aldehyde in the presence of NADH. Ifthe dehydrogenase and esterase activities are catalysed at the same enzymic active site, the observations of Kitson (1978), MacGibbon et al (1978) and Nousiainen et al (1978) should be explicable in terms of the present hypothesis. The data of Nousiainen et al (1978) do not rule out the existence of aldehyde dehydrogenase and 4-nitrophenyl esterase activities on the same protein; an equally valid explanation is that there is more than one type of esterase, with most of the activity not being contributed by the phenobarbital-inducible aldehyde dehydrogenase.…”

“…It has generally been assumed that the aldehyde dehydrogenase and the 4-nitrophenyl esterase reactions are catalysed by the same protein at the same active site, but recently some doubt has been cast on this assumption. Almost complete inhibition of the dehydrogenase activity of aldehyde dehydrogenase from the cytoplasm of sheep liver by disulfiram (tetraethylthiuram disulphide) results in only slight inhibition of the associated esterase (Kitson, 1978), and both chloral hydrate and NAD+ differentially inhibit the dehydrogenase and esterase activities of the enzyme(s) from the same source (MacGibbon et al, 1978). In addition, differential induction of aldehyde dehydrogenase and 4-nitrophenyl esterase by phenobarbital in the cytoplasm of the liver of the rat suggests that the two activities may be controlled by distinct genetic factors (Nousiainen et al, 1978).…”

A Reinvestigation of the Purity, Isoelectric Points and Some Kinetic Properties of the Aldehyde Dehydrogenases from Sheep Liver

“…Studics or the effect of the thiol reagent disulfiram (tetraethyl thiuram disulphide) on both aldehyde dehydrogenases have shown that the cytoplasmic enzyme is much more sensitive to inactivation by this inhibitor . When two inolecules of disulfiram are added per molecule of enzyme tctramer, 90% of the initial cytoplasmic enzyme activity is lost [9], while only about 30 of the, mitochondrial activity is lost [lo]. The residual activity for both enzymes is relatively insensitive to further increases in the concentration of disulfiram.…”