Human Aldehyde Dehydrogenase Isozymes Research Articles

Proteomic alterations of the variants of human aldehyde dehydrogenase isozymes correlate with hepatocellular carcinoma.

To develop novel markers for hepatocellular carcinomas (HCC), 10 cases were analyzed by 2-dimensional electrophoresis (2DE) and matrix-assisted laser desorption ionization mass spectrometry. Results were compared to those of paired adjacent nontumorous liver tissues. Comparative analysis of the respective spot patterns in 2DE revealed that 3 variants of class 3 aldehyde dehydrogenase (ALDH-3) newly appeared while 2 variants of ALDH-2 diminished to undetectable levels in HCC. However, 4 ALDH-1 variants with different pIs remained unaffected. This pattern of concomitant appearance and disappearance of ALDH-3 and ALDH-2 variants was consistently observed in all HCC tissues. Our results suggest that alterations of ALDH isozyme variants may be closely correlated to HCC and that proteomic analysis of these proteins might be a novel approach to identify the molecular events in detail during hepatocarcinogenesis.

N-tosyl-L-phenylalanine chloromethyl ketone, a serine protease inhibitor, identifies glutamate 398 at the coenzyme-binding site of human aldehyde dehydrogenase. Evidence for a second "naked anion" at the active site.

Human aldehyde dehydrogenase isozymes were inactivated by N-tosyl-L-phenylalanine chloromethyl ketone (TPCK), an inhibitor of chymotrypsin. The inactivation was a first-order process that followed saturation kinetics. NAD and chloral when used together protected against inactivation. In steady-state kinetics, TPCK produced only slope effects versus varied NAD, both slope and intercept effects versus varied glycolaldehyde were produced, indicating that TPCK reacted with the same enzyme form with which NAD reacted. Ki values from steady-state kinetics and saturation kinetics were comparable. Use of [3H]-labeled TPCK showed that inactivation was associated with the incorporation of two molecules of TPCK per molecule of enzyme. The label incorporation occurred into a single tryptic peptide and also into a single chymotryptic peptide of the E1 isozyme. Purification of labeled peptides, followed by sequencing, demonstrated that E398 of aldehyde dehydrogenase was labeled. Reaction of a haloketone, TPCK, with a carboxyl group of E398 indicates that E398 occurs as a "naked anion" within the molecule. This paper constitutes identification of the second (after E268) "naked anion" at the active site of aldehyde dehydrogenase.

Human ocular aldehyde dehydrogenase isozymes: Distribution and properties as major soluble proteins in cornea and lens

Human aldehyde dehydrogenase isozymes (ALDHs; EC 1.2.1.3) exhibit very high levels of activity in anterior eye tissues. Human corneal ALDH1 and ALDH3 isozymes are present as major soluble proteins (3% and 5%, respectively, of corneal soluble protein) and may play major roles in protecting the cornea against ultraviolet radiation (UVR)-induced tissue damage, as well as contributing directly to ultraviolet B (UV-B) photoreception. The human lens exhibits high levels of ALDH1 activity (1-2% of lens-soluble protein) and lower levels of ALDH3 activity. Kinetic analyses support a role for these enzymes in the metabolism of peroxidic aldehydes, which have been reported in ocular tissues.

Cloning and characterization of genes encoding four additional human aldehyde dehydrogenase isozymes.

Aldehyde dehydrogenases (ALDH; aldehyde:NAD+ oxidoreductase, EC 1.2.1.3) are a group of isozymes with broad substrate specificity. They catalyze the oxidation of various aliphatic and aromatic aldehydes to the corresponding acids (Pietruszko, 1983) and have been frequently considered as detoxifying enzymes which eliminate aldehydes in vivo. Metabolism of ethanol-derived acetaldehyde and toxic aldehyde in the foodstuff and from lipid peroxidation are examples of the detoxification role of the ALDH isozymes (Parrilla et al, 1974; Harrington et al, 1987; Mitchell et al., 1987; Jakoby et al., 1990). Recently, it has been demonstrated that the enzymes also play crucial roles in the metabolism of retinoic acid, biogenic amine and neurotransmitters (Ambroziak and Pietruszko, 1991, 1993; Yoshida et al., 1992, 1993).KeywordsAldehyde DehydrogenaseHuman Salivary GlandALDH GeneAldehyde Dehydrogenase GeneImportant Amino Acid ResidueThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Detoxification of cyclophosphamide by human aldehyde dehydrogenase isozymes

In in vitro studies, no turnover of aldophosphamide and mafosfamide was observed with the tumor-specific aldehyde dehydrogenase 3 isozyme (ALDH3) isolated from human stomach mucosa as well as from lung (A549) and pharynx (UMSCC2) carcinoma cell lines. Only the human liver cytosolic ALDH preparation (ALDH1) showed any significant oxidation of aldophosphamide and mafosfamide.

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.

Electrophoretic and biochemical studies of human aldehyde dehydrogenase isozymes in various tissues

Four major ALDH isozymes have been identified in human tissues using starch gel electrophoresis and isoelectric focusing. The isozyme bands have been termed as ALDH I, II, III and IV according to their decreasing electrophoretic migration and increasing isoelectric point. The isozymes have been partially purified via preparative isoelectric focusing. Kinetic characteristics of ALDH I and II were found to be quite similar to ALDH enzyme 2 and enzyme 1 described earlier by Greenfield and Pietruszko (Biochem Biophys Acta, 483 35–45 1977). ALDH III and IV showed a very high Km for propionaldehyde (1.0–1.5 mM at pH 9.5) and were not inhibited by disulfiram at pH 9.5. A variant phenotype of ALDH which lacked in isozyme I was detected in various tissues from Japanese individuals. Comparative kinetic properties of normal and variant enzyme are given.