A specific affinity reagent to distinguish aldehyde dehydrogenases and oxidases. Enzymes catalyzing aldehyde oxidation in an adult moth

Characterization of rat glutathione transferases in olfactory epithelium and mucus

The olfactory epithelium is continuously exposed to exogenous chemicals, including odorants. During the past decade, the enzymes surrounding the olfactory receptors have been shown to make an important contribution to the process of olfaction. Mammalian xenobiotic metabolizing enzymes, such as cytochrome P450, esterases and glutathione transferases (GSTs), have been shown to participate in odorant clearance from the olfactory receptor environment, consequently contributing to the maintenance of sensitivity toward odorants. GSTs have previously been shown to be involved in numerous physiological processes, including detoxification, steroid hormone biosynthesis, and amino acid catabolism. These enzymes ensure either the capture or the glutathione conjugation of a large number of ligands. Using a multi-technique approach (proteomic, immunocytochemistry and activity assays), our results indicate that GSTs play an important role in the rat olfactory process. First, proteomic analysis demonstrated the presence of different putative odorant metabolizing enzymes, including different GSTs, in the rat nasal mucus. Second, GST expression was investigated in situ in rat olfactory tissues using immunohistochemical methods. Third, the activity of the main GST (GSTM2) odorant was studied with in vitro experiments. Recombinant GSTM2 was used to screen a set of odorants and characterize the nature of its interaction with the odorants. Our results support a significant role of GSTs in the modulation of odorant availability for receptors in the peripheral olfactory process.

Molecular characterization of the amplified aldehyde oxidase from insecticide resistant Culex quinquefasciatus

Primary structural information including the complete nucleotide sequence of the first insect aldehyde oxidase (AO) was obtained from the common house mosquito Culex quinquefasciatus (Say) through cloning and sequencing of both genomic DNA and cDNA. The deduced amino-acid sequence encodes a 150-kDa protein of 1266 amino-acid residues, which is consistent with the expected monomeric subunit size of AO. The Culex AO sequence contains a molybdopterin cofactor binding domain and two iron-sulfur centres. A comparison of the partial sequences of AO from insecticide resistant and susceptible strains of C. quinquefasciatus shows two distinct alleles of this enzyme, one of which is amplified in the insecticide resistant strain on a 30-kb DNA amplicon alongside two resistance-associated esterases. The amplified AO gene results in elevated AO activity in all life stages, but activity is highest in 3rd instar larvae. The elevated enzyme can be seen as a separate band on polyacrylamide gel electrophoresis. The role of AO in xenobiotic oxidation in mammals and the partial inhibition of elevated AO activity by a range of insecticides in Culex, suggest that this AO may play a role in insecticide resistance.

The first structure of an aldehyde dehydrogenase reveals novel interactions between NAD and the Rossmann fold

The first structure of an aldehyde dehydrogenase (ALDH) is described at 2.6 A resolution. Each subunit of the dimeric enzyme contains an NAD-binding domain, a catalytic domain and a bridging domain. At the interface of these domains is a 15 A long funnel-shaped passage with a 6 x 12 A opening leading to a putative catalytic pocket. A new mode of NAD binding, which differs substantially from the classic beta-alpha-beta binding mode associated with the 'Rossmann fold', is observed which we term the beta-alpha,beta mode. Sequence comparisons of the class 3 ALDH with other ALDHs indicate a similar polypeptide fold, novel NAD-binding mode and catalytic site for this family. A mechanism for enzymatic specificity and activity is postulated.

Biosynthesis and metabolism of 2-iodohexadecanal in cultured dog thyroid cells

2-Iodohexadecanal (2-IHDA) is a major thyroid iodolipid. It mimics the main regulatory effects of iodide on thyroid metabolism: inhibition of H2O2 production and of adenylyl cyclase. The biosynthesis of 2-IHDA and its metabolism have been investigated in cultured dog thyroid cells maintained in a differentiated state by forskolin. Incubation of these cells with [9,10-3H]hexadecan-1-ol or [9,10-3H]palmitic acid labeled several phospholipids, but [9, 10-3H]hexadecan-1-ol was selectively incorporated into plasmenylethanolamine. In the presence of an exogenous H2O2 generating system (glucose oxidase), iodide induced the production of [9,10-3H]2-IHDA from [9,10-3H]hexadecan-1-ol-labeled cells but not from [9,10-3H]palmitic acid-labeled cells. 2-IHDA was also generated during the lactoperoxidase-catalyzed iodination of brain and heart plasmalogens, and of ethyl hexadec-1-enyl ether, a synthetic vinyl ether-containing compound. Taken together, these results show that thyroid 2-IHDA is derived from plasmenylethanolamine via an attack of reactive iodine on the vinyl ether group. 2-Iodohexadecan-1-ol (2-IHDO) was also detected in these studies; it was formed later than 2-IHDA, and thyroid cells converted exogenous 2-IHDA into 2-IHDO in a time-dependent way. The ratio of 2-IHDO/2-IHDA increased with H2O2 production and decreased as a function of iodide concentration. An aldehyde-reducing activity was detected in subcellular fractions of the horse thyroid. No formation of 2-iodohexadecanoic acid could be detected. Reduction into the biologically inactive 2-IHDO is thus a major metabolic pathway of 2-IHDA in dog thyrocytes.

The molybdoenzymes xanthine oxidase and aldehyde oxidase contain fast- and slow-DTNB reacting sulphydryl groups

The reactivities with an excess of 5-5'-dithiobis (2-nitrobenzoic) acid (DTNB) of sulphydryl residues present in xanthine oxidase and aldehyde oxidase were studied and compared. The results show that two classes of sulphydryl groups with quite different reactivities exist in both enzymes either native or denatured. Some of the available sulphydryl residues thus react instantaneously with the DTNB, whereas the others react very slowly following pseudo-first-order kinetics. The number of sulphydryl residues of each class and the rate constant of slowly reacting groups are, respectively, 1.7 and 0.8 in native xanthine oxidase and 1.6 and 1.7 in native aldehyde oxidase. In denatured enzymes, the number of fast- and slow-reacting sulphydryl residues obtained are, respectively, 13.9 and 7.9 in xanthine oxidase and 5.7 and 5.4 in aldehyde oxidase. Analogously, the rate constant for the slowly reacting groups is similar for the two native enzymes, but in denatured aldehyde oxidase it is double that of denatured xanthine oxidase.

Aldehyde-oxidizing enzymes in an adult moth: in vitro study of aldehyde metabolism in Heliothis virescens

The conversion of pheromonal aldehydes to carboxylic acids in vitro in tissue extracts of Heliothis virescens is catalyzed by both aldehyde dehydrogenase and aldehyde oxidase enzymes. The aldehyde-oxidizing activity in antennae, heads, legs, and hemolymph from male and female moths was examined by radiochromatographic and spectroscopic assays. First, the enzymatic activity was measured in the presence or absence of added NAD+ using either (Z)-9-tetradecenal or (Z)-11-hexadecenal as tritiated substrate. Second, substrate specificity was determined spectroscopically by (i) indirect measurement of the AO-released hydrogen peroxide through the coupled AO-horseradish peroxidase reaction and by (ii) direct measurement of the ALDH-produced NADH. Both aldehyde-oxidizing activities were associated with soluble enzymes in the antennal extracts, and these enzymes degraded pheromone and nonpheromonal aldehydes. Both AO and ALDH activities were present in male and female tissues. AO activity was exhibited primarily in the antennal extracts and to a lesser degree in the leg extracts. Moreover, ALDH activity was distributed in the antenna, head, and leg extracts. A vinyl ketone analog of (Z)-11-hexadecenal preferentially inhibited the ALDH activity over the AO activity.