Stereoselective reduction of 4-benzoylpyridine by recombinant pig heart carbonyl reductase

Crystal structure of (RS)-(4-chloro-phen-yl)(pyridin-2-yl)methanol

In the title racemic compound, C12H10ClNO, the dihedral angle between the benzene and pyridine rings is 74.34 (6)°. In the crystal, the mol-ecules are linked by O-H⋯N hydrogen bonds, forming zigzag C(5) [001] chains in which alternating R- and S-configuration mol-ecules are related by c-glide symmetry. In addition, inversion-related pairs of mol-ecules are linked into dimers by pairs of weak C-Cl⋯π(pyrid-yl) inter-actions, which link the hydrogen-bonded chains into (100) sheets. Structural comparisons are drawn with a number of related compounds.

Comparative inhibition of tetrameric carbonyl reductase activity in pig heart cytosol by alkyl 4-pyridyl ketones

CONTEXT AND OBJECTIVE

The present study is to elucidate the comparative inhibition of tetrameric carbonyl reductase (TCBR) activity by alkyl 4-pyridyl ketones, and to characterize its substrate-binding domain.

MATERIALS AND METHODS

The inhibitory effects of alkyl 4-pyridyl ketones on the stereoselective reduction of 4-benzoylpyridine (4-BP) catalyzed by TCBR were examined in the cytosolic fraction of pig heart.

RESULTS

Of alkyl 4-pyridyl ketones, 4-hexanoylpyridine, which has a straight-chain alkyl group of five carbon atoms, inhibited most potently TCBR activity and was a competitive inhibitor. Furthermore, cyclohexyl pentyl ketone, which is substituted by cyclohexyl group instead of phenyl group of hexanophenone, had much lower ability to be reduced than hexanophenone.

DISCUSSION AND CONCLUSION

These results suggest that in addition to a hydrophobic cleft corresponding to a straight-chain alkyl group of five carbon atoms, a hydrophobic pocket with affinity for an aromatic group is located in the substrate-binding domain of TCBR.

Possible mechanism of superoxide formation through redox cycling of plumbagin in pig heart

The purpose of this study is to elucidate the possible mechanism of superoxide formation through redox cycling of plumbagin (PLG) in pig heart. Of four 1,4-naphthoquinones tested in this study, PLG was most efficiently reduced in the cytosolic fraction of pig heart. On the other hand, lawsone (LAS) was little reduced. Thus, whether or not PLG and LAS induce the formation of superoxide anion radical in pig heart cytosol was examined, by using the methods of cytochrome c reduction and chemiluminescence. PLG significantly induced the formation of superoxide anion radical, even though LAS had no ability to mediate superoxide formation. PLG was a significant inhibitor for the stereoselective reduction of 4-benzoylpyridine (4-BP) catalyzed by tetrameric carbonyl reductase (TCBR) in pig heart cytosol. Furthermore, PLG was confirmed to competitively inhibit the 4-BP reduction, and the optimal pH for the PLG reduction was around 6.0 similar to that for the 4-BP reduction. These results suggest that PLG mediates superoxide formation through its redox cycling involved in the two-electron reduction catalyzed by TCBR, and induces oxidative stress in pig heart.

[Structure and function of peroxisomal tetrameric carbonyl reductase]

In this paper, the structure and function of a new tetrameric carbonyl reductase (TCR) is reviewed. TCRs were purified from rabbit and pig heart, using 4-benzoylpyridine as a substrate. Partial peptide sequencing and cDNA cloning of rabbit and pig TCRs revealed that both enzymes belonged to the short-chain dehydrogenase/reductase family and that their subunits consisted of 260 amino acid residues. Rabbit and pig TCRs catalyzed the reduction of alkyl phenyl ketones, alpha-dicarbonyl compounds, quinones and retinals. Both enzymes were potently inhibited by flavonoids and fatty acids. 9,10-Phenanthrenequinone, which is efficiently reduced by rabbit and pig TCRs, mediated the formation of superoxide radical through its redox cycling in pig heart. The C-terminal sequences of rabbit and pig TCRs comprised a type 1 peroxisomal targeting signal (PTS1) Ser-Arg-Leu, suggesting that the enzymes are localized in the peroxisome. In fact, pig TCR was targeted into the peroxisomal matrix, in the case of transfection of HeLa cells with vectors expressing the enzyme. However, when the recombinant pig TCR was directly introduced into HeLa cells, the enzyme was not targeted into the peroxisomal matrix. The crystal structure of recombinant pig TCR demonstrated that the C-terminal PTS1 of each subunit of the enzyme was buried in the interior of the tetrameric molecule. These findings indicate that pig TCR is imported into the peroxisome as a monomer and then forms an active tetramer within this organelle.

Inhibition of carbonyl reductase activity in pig heart by alkyl phenyl ketones

The inhibitory effects of alkyl phenyl ketones on carbonyl reductase activity were examined in pig heart. In this study, carbonyl reductase activity was estimated as the ability to reduce 4-benzoylpyridine to S(-)-alpha-phenyl-4-pyridylmethanol in the cytosolic fraction from pig heart (pig heart cytosol). The order of their inhibitory potencies was hexanophenone > valerophenone > heptanophenone > butyrophenone > propiophenone. The inhibitory potencies of acetophenone and nonanophenone were much lower. A significant relationship was observed between Vmax/Km values for the reduction of alkyl phenyl ketones and their inhibitory potencies for carbonyl reductase activity in pig heart cytosol. Furthermore, hexanophenone was a competitive inhibitor for the enzyme activity. These results indicate that several alkyl phenyl ketones including hexanophenone inhibit carbonyl reductase activity in pig heart cytosol, by acting as substrate inhibitors.

Stereoselective reduction of 4-benzoylpyridine in the heart of vertebrates

The stereoselectivity in the reduction of 4-benzoylpyridine (4-BP) was examined in the cytosolic fractions from the heart of 9 vertebrates (pig, rabbit, guinea pig, rat, mouse, chicken, soft-shelled turtle, frog and flounder). 4-BP was stereoselectively reduced to S(-)-alpha-phenyl-4-pyridylmethanol [S(-)-PPOL] in the cytosolic fractions from the heart of pig, rabbit and guinea pig. However, of mammalian heart cytsol tested, only rat heart cytosol had little ability to reduce stereoselectively 4-BP. In an attempt to elucidate this reason, amino acid sequence of rat heart carbonyl reductase (RatHCR) was deduced from the cloned cDNA and compared with that of pig heart carbonyl reductase (PigHCR), which shows a high stereoselectivity in the reduction of 4-BP to S(-)-PPOL. RatHCR showed a high identity with PigHCR in amino acid sequence. Furthermore, recombinant RatHCR was confirmed to reduce stereoselectively 4-BP to S(-)-PPOL with a high optical purity comparable to recombinant PigHCR. It is possible that in the cytosolic fraction from the heart of rat, constitutive reductase other than RatHCR counteracts the stereoselective reduction of 4-BP to S(-)-PPOL, by catalyzing the reduction of 4-BP to the R(+)-enantiomer.

Effects of quinones and flavonoids on the reduction of all-trans retinal to all-trans retinol in pig heart

We have recently purified a tetrameric carbonyl reductase from the cytosolic fraction of pig heart (pig heart carbonyl reductase). Since pig heart carbonyl reductase efficiently reduces all-trans retinal as the endogenous substrate, it probably plays an important role in retinoid metabolism in the heart. The purpose of the present study was to evaluate the inhibitory effects of quinones and flavonoids on the reduction of all-trans retinal to all-trans retinol catalyzed by pig heart carbonyl reductase, using pig heart cytosol. Of quinones tested, 9,10-phenanthrenequinone, a component of diesel exhaust particles, was the most potent inhibitor for the all-trans retinal reduction, and a significant inhibition was also observed for plumbagin and menadione. The order of the inhibitory potencies for flavonoids was kaempferol > quercetin > genistein > myricetin = apigenin = daidzein. However, the inhibitory potencies of flavonoids were much lower than that of 9,10-phenanthrenequinone. 9,10-Phenanthrenequinone competitively inhibited the all-trans retinal reduction, whereas kaempferol exhibited a mixed-type inhibition. It is likely that 9,10-phenanthrenequinone strongly inhibits the reduction of all-trans retinal to all-trans retinol by acting as the substrate inhibitor of pig heart carbonyl reductase present in pig heart cytosol.

Involvement of carbonyl reductase in superoxide formation through redox cycling of adrenochrome and 9,10-phenanthrenequinone in pig heart

The effects of adrenochrome, a metabolite of epinephrine (adrenaline), and 9,10-phenanthrenequinone (PQ), a component of diesel exhaust particles, on the stereoselective reduction of 4-benzoylpyridine (4-BP) were examined in pig heart cytosol. PQ was a potent inhibitor for the 4-BP reduction, while adrenochrome was a poor inhibitor. A similar result was observed in the effects of adrenochrome and PQ on the reduction of all-trans retinal. Furthermore, although PQ mediated efficiently the formation of superoxide anion radical through its redox cycling in pig heart cytosol, adrenochrome had no ability to mediate the superoxide formation. These may be because the reactivity for adrenochrome, catalyzed by pig heart carbonyl reductase (PHCR), is much lower than that for PQ. The optimal pH for the reduction of PQ in pig heart cytosol was around 5.5. Dicumarol, a potent inhibitor of DT-diaphorase, had little effect on the time course of NADPH oxidation during the reduction of PQ. Therefore, it is concluded that PHCR plays a critical role in superoxide formation through redox cycling of PQ.