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Aldehyde reductase from human liver catalyzes the hydrogen transfer from the pro-4R position on the dihydronicotinamide ring of the coenzyme to the re face of the carbonyl carbon atom of the substrate.
Pig kidney aldehyde reductase is inactivated by 2,3-butanedione, phenylglyoxal, methylglyoxal, and 1,2-cyclohexanedione. 2,3-Butanedione caused the most rapid loss in enzyme activity, the rate of loss being proportional to the concentration of 2,3-butanedione. Neither D-glyceraldehyde nor pyridine 3-aldehyde, both substrates for this broadly specific enzyme, protected the enzyme from inactivation but 1 mM NADPH or NADP completely prevented the loss of activity by 2,3-butanedione suggesting the involvement of arginine in the binding of cofactor. Nicotinamide mononucleotide (NMN) (reduced form) offered no protection to inactivation whereas ADP-ribose phosphate gave complete protection indicating that it is the latter portion of NADPH which interacts with the essential arginine. Both NMN and ADP-ribose phosphate are competitive inhibitors of aldehyde reductase with respect to NADPH. Butanedione-modified aldehyde reductase could still bind to a blue dextran-Sepharose 4B column suggesting that the modified arginine did not bind NADPH. This was confirmed by fluorescence spectra which showed that chemically modified aldehyde reductase caused the same blue shift of NADPH fluorescence as did native aldehyde reductase. Of additional interest was the quenching of NADPH fluorescence by aldehyde reductase which, with one exception, is in contrast to the fluorescence behavior of all other oxidoreductases.
An aldehyde reductase (EC 1.1.1.2) from human liver has been purified to homogeneity. The enzyme is NADPH-dependent, prefers aromatic to aliphatic aldehydes as substrates, and is inhibited by barbiturates and hydantoins. The following physicochemical parameters were determined: molecular weight, 36,200; sedimentation coefficient, 2.9 S; Stokes radius, 2.65 nm; isoelectric point, pH 5.3; extinction coefficient at 280 nm, 54,300 M-1 cm-1. Results from polyacrylamide gel electrophoresis with and without sodium dodecyl sulfate, gel filtration, and ultracentrifugation suggest a monomeric structure. On molecule of NADPH binds to the enzyme causing a red shift of the coenzyme absorption maximum from 340 to 352 nm. The amino acid composition has been determined and a partial specific volume of 0.74 was computed from these data. An alpha-helicity of 7 and 18% was estimated from the ellipticities at 208 and 222 nm, respectively. Combination of the most reactive thiol group with p-mercuribenzoate does not cause loss of catalytic activity. Inactivation occurs when more than one thiol group is modified. The presence of NADPH or NADP+ prevents loss of activity by thiol modification. The comparison of structural features of aldehyde reductase with other monomeric and oligomeric dehydrogenases suggest similarities of aldehyde reductase with octopine dehydrogenase.
An improved procedure for purifying aldehyde reductase is described. Utilization of Blue Dextran--Sepharose 4B and elimination of hydroxyapatite chromatography greatly improves the yield and ease of purification. Starting with 340 g of kidney tissue (two pig kidneys) approx. 50 mg of purified reductase may be routinely and reproducibly obtained. The purified reductase was used to establish the kinetic reaction mechanism of the enzyme. Initial-velocity analysis and product-inhibition data revealed that pig kidney aldehyde reductase follows an Ordered Bi Bi reaction mechanism in which NADPH binds first before D-glyceraldehyde. The limiting Michaelis constants for D-glyceraldehyde and NADPH were 4.8 +/- 0.7 mM and 9.1 +/- 2.1 micrometer respectively. The mechanism is similar to that of another monomeric oxidoreductase, octopine dehydrogenase, towards which aldehyde reductase exhibits several similarities, but differs from that of other aldehyde reductases. Phenobarbital is a potent inhibitor of aldehyde reductase, inhibiting both substrate and cofactor non-competitively (Ki = 80.4 +/- 10.5 micrometer and 66.9 +/- 1.6 micrometer respectively). Barbiturate inhibition seems to be a common property of NADPH-dependent aldehyde reductases.
The amino acid compositions of several monomeric NADPH-dependent aldehyde reductases from a variety of species have been determined and analyzed by the difference index method of Metzger et al. (1968). The difference indexes among mammals range from 4.15 - 6.10 indicating considerable homology. Comparison of chicken aldehyde reductase with mammalian aldehyde reductases gave values in the range 6.8 - 9.9 suggesting a close relationship whereas the difference indexes for the enzymes from fruit fly and Baker's yeast versus vertebrate aldehyde reductases (10.9 - 14.4) indicate more distant relationships. The extent of sequence homology among aldehyde reductases from these species was estimated from a plot of difference index versus percent sequence difference for oxido-reductases of known sequence. From this plot, and using a mammal-chicken divergence time of 300 million years and a mammalian order split of 75 million years, the rate of evolution of aldehyde reductases was calculated to lie in the range 5.8 - 15.6% sequence difference per 100 million years. Comparison with rates of evolution of oligomeric dehydrogenases indicates that aldehyde reductases comprise the most rapidly evolving family of oxido-reductases. This is probably related to the monomericity of aldehyde reductases since there is a direct correlation between the number of subunits and the rate of evolution.
Investigation of NADP-dependent aldehyde reductase activity in mouse liver led to the finding that two distinct reductases are separable by DE52 ion exchange chromatography. Aldehyde reductase I (AR I) appears in the effluent, while aldehyde reductase II (AR II) is eluted with a salt gradient. By several procedures AR II was purified over 1100-fold from liver supernatant fraction, but AR I could be pruified only 107-fold because of its instability. The two enzymes are different in regard to pH optimum, substrate specificity, response to inhibitors, and reactivity with antibody to AR II. While both enzymes utilize aromatic aldehydes well, only AR II ACTS ON D-glucuronate, indicating that it is the aldyhyde reductase recently reported to be identical to NADP-L-gulonate dehydrogenase. The presence of two NADP-linked aldehyde reductases in liver has apparently not heretofore been reported.
Amidination of human liver aldehyde reductase (alcohol:NADP+ oxidoreductase, EC 1.1.1.2) with monofunctional n-alkane methylimidates increased the enzymic activity by 10--30%, whereas analogous bifunctional imidoesters caused a loss of activity of about 80%. Both effects were prevented in the presence of the coenzyme NADPH or NADP+, but not of the substrate 4-nitrobenzaldehyde. Amidination increased the apparent Michaelis constant of both the coenzyme (up to 20-fold) and the substrate (about 5-fold). Bifunctional imidoesters with at least 4 carbon atoms between the functional groups (approx. 0.7 nm) crosslinked the enzyme intramolecularly. This reaction was retarded in the presence of the coenzyme, whereas 4-nitrobenzaldehyde had no effect. The results suggest the presence of reactive amino groups at the coenzyme binding site of aldehyde reductase.
1. NADPH-dependent aldehyde reductase (AR) is widely distributed among animal species. It also occurs in flowering plants and fungi (yeast). 2. AR is located mainly in the kidney or renal tissue of all species examined, with the exception of fish where it occurs mainly in the liver. 3. The enzyme from each species is monomeric and has a molecular weight between 30,000 and 40,000 daltons. 4. The enzymes exhibit similar substrate specificities and pH profiles and are inhibited by barbiturates. 5. In the reduction of D-glyceraldehyde the monomeric AR of each species catalyzes the stereospecific transfer of the A hydrogen from NADPH.
Some physical and chemical properties of the monomeric NADP+-dependent aldehyde reductase (previously called TPN-L-hexonate dehydrogenase or D-glucuronate reductase) from pig kidney have been examined. The amino acid composition has been determined. Four of the five thiol groups react with p-mercuribenzoate at pH 7, with no resulting loss of catalytic activity. High concentrations of p-mercuribenzoate cause complete enzyme inhibition, which can be partly reversed by addition of aldehyde reductase is low (9%, estimated from the ellipticity at 208 nm), and 70 to 80% of the tyrosine and tryptophan residues aare buried within the molecule. One molecule of NADPH binds to the enzyme (Kp equal 25 muM), causing a blue shift and enhancement of the coenzyme fluorescence, and suggesting that the environment of the active site is hydrophobic. In the reduction of D-glyceraldehyde, catalyzed by aldehyde reductase, the pro-4R "A" hydrogen of NADPH attacks the re face of the carbonyl group. This stereospecificity is the same as in the reductions of D-glyceraldehyde and acetaldehyde effected by rabbit muscle dehydrogenase and liver alcohol dehydrogenase, respectively.
Two succinic semi-aldehyde reductases (A and B) have been purified to electrophoretic homogeneity. Enzyme A, which is a monomer of molecular weight 40,000 +/- 5,000 reduces a wide range of aldehydes and is inhibited by some barbiturates and certain anticonvulsants. Enzyme B, which is a dimer of molecular weight 80,000 +/- 10,000, is very specific for succinic semi-aldehyde and is not inhibited by the aforementioned compounds.
The effect of long-term administration of phenobarbital (PB) or barbital for five weeks on brain aldehyde reductase (A1R) and aldehyde dehydrogenase (A1DH) activities in the rat was studied. Mitochondrial (m)-A1DH and NADH-dependent A1R activities were significantly increased over control values after five-week treatment with PB or barbital, while no significant alteration of supernatant (s)-A1DH and NADPH-dependent A1R activities was observed under the same condition. Increase in m-A1DH activity by the treatment with barbiturates was recovered to the control level, however, increased activity of NADH-dependent A1R was maintained even after the cessation of the treatment. In groups of rats pretreated with barbiturates for five weeks, no animals were induced to sleep after intracerebroventricular injection of PB, and this finding strongly suggests the decrease in sensitivity of rats to barbiturates.
The synthesis and characterization of the addition product of NADP and decanaldehyde are described. This adduct is an inhibitor of beef brain NADP-linked aldehyde reductase (Ki = 2.3 x 10(-6) M) along with the NADP adducts of butyraldehyde, phenylpropionaldehyde, and phenylacetaldehyde.
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