Kosuke Ichihara

Characterization of the ybdT gene product of Bacillus subtilis: Novel fatty acid β-hydroxylating cytochrome P450

We have characterized the gene encoding fatty acid α-hydroxylase, a cytochrome P450 (P450) enzyme, from Sphingomonas paucimobilis. A database homology search indicated that the deduced amino acid sequence of this gene product was 44% identical to that of the ybdT gene product that is a 48 kDa protein of unknown function from Bacillus subtilis. In this study, we cloned the ybdT gene and characterized this gene product using a recombinant enzyme to clarify function of the ybdT gene product. The carbon monoxide difference spectrum of the recombinant enzyme showed the characteristic one of P450. In the presence of H2O2, the recombinant ybdT gene product hydroxylated myristic acid to produce β-hydroxyristic acid and α-hydroxymyristic acid which were determined by high-performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry. The amount of these products increased with increasing reaction period and amount of H2O2 in the reaction mixture. The amount of β-hydroxyl product was slightly higher than that of α-hydroxyl product at all times during the reaction. However, no reaction products were detected at any time or at any concentration of H2O2 when heat-inactivated enzyme was used. HPLC analysis with a chiral column showed that the β-hydroxyl product was nearly enantiomerically pure R-form. These results suggest that this P450 enzyme is involved in a novel biosynthesis of β-hydroxy fatty acid.

Fatty acid-specific, regiospecific, and stereospecific hydroxylation by cytochrome P450 (CYP152B1) from Sphingomonas paucimobilis: Substrate structure required for α-hydroxylation

Fatty acid α-hydroxylase from Sphingomonas paucimobilis is an unusual cytochrome P450 enzyme that hydroxylates the α-carbon of fatty acids in the presence of H2O2. Herein, we describe our investigation concerning the utilization of various substrates and the optical configuration of the α-hydroxyl product using a recombinant form of this enzyme. This enzyme can metabolize saturated fatty acids with carbon chain lengths of more than 10. The Km value for pentadecanoic acid (C15) was the smallest among the saturated fatty acids tested (C10–C18) and that for myristic acid (C14) showed similar enzyme kinetics to those seen for C15. As shorter or longer carbon chain lengths were used, Km values increased. The turnover numbers for fatty acids with carbon chain lengths of more than 11 were of the same order of magnitude (103 min−1), but the turnover number for undecanoic acid (C11) was less. Dicarboxylic fatty acids and methyl myristate were not metabolized, but monomethyl hexadecanedioate and ω-hydroxypalmitic acid were metabolized, though with lower turnover values. Arachidonic acid was a good substrate, comparable to C14 or C15. The metabolite of arachidonic acid was only α-hydroxyarachidonic acid. Alkanes, fatty alcohols, and fatty aldehydes were not utilized as substrates. Analysis of the optical configurations of the α-hydroxylated products demonstrated that the products were S-enantiomers (more than 98% enantiomerically pure). These results suggested that this P450 enzyme is strictly responsible for fatty acids and catalyzes highly stereo- and regioselective hydroxylation, where structure of ω-carbon and carboxyl carbon as well as carbon chain length of fatty acids are important for substrate-enzyme interaction.

Direct involvement of hydrogen peroxide in bacterial α-hydroxylation of fatty acid

We have reported that fatty‐acid α‐hydroxylase partially purified from Sphingomonas paucimobilis required NADH and molecular oxygen. In this study, we found that the reaction was greatly inhibited by catalase. Glutathione and glutathione peroxidase also inhibited α‐hydroxylation, but superoxide dismutase and mannitol did not. Replacement of NADH and molecular oxygen by hydrogen peroxide increased the α‐hydroxylation activity. In the presence of hydrogen peroxide, molecular oxygen was not required for the activity. These findings suggest that hydrogen peroxide was essential for bacterial α‐hydroxylase.

Superoxide dismutase from Mycobacterium species, strain Takeo

Superoxide dismutase from Mycobacterium species, strain Takeo, has been purified to homogeneity as judged by disc gel electrophoresis and ultracentrifugation. The enzyme was found to have a molecular weight of approximately 61 500 by sedimentation equilibrium and to contain manganese by atomic absorption and electron spin resonance spectra. The amino acid composition was also determined. The enzyme was considerably stable to the treatment with sodium dodecyl sulfate; unless incubating at 80°C for 2 min, it was not completely dissociated into the subunits. The molecular weight of the subunit was found to be approximately 21 000. Antibodies against the superoxide dismutase were produced by immunization of rabbits with the enzyme, and the γ-globulin fraction was purified. Superoxide dismutase preparations obtained from various species of mycobacteria and nocardia cross-reacted to different degrees with these antibodies on the Ouchterlony double diffusion plates. Comparative immunological studies indicated that strain Takeo might be most closely related to Myobacterium smegmatis among species of mycobacteria and nocardia tested. The antibodies against superoxide dismutase may be used as a valuable tool for the classification of mycobacteria.

Crystallization and preliminary X-ray diffraction analysis of fatty-acid hydroxylase cytochrome P450BSβ from Bacillus subtilis

Cytochrome P450 isolated from Bacillus subtilis (P450BSβ; MW 48 kDa) catalyzes the hydroxylation of long-chain fatty acids at the α and β positions using H2O2 as an oxidant. Crystals of the substrate-free form of P450BSβ belonging to the trigonal space group P3221 or P3121 were obtained by the sitting-drop vapour-diffusion method using a precipitate solution consisting of 10%(w/v) PEG 4000 and 50 mM MES pH 6.8. Another crystal form, belonging to the rhombohedral space group R3 or R32, was obtained from precipitate solution consisting of 10% PEG 4000, 0.15 mM magnesium acetate and 50 mM MES pH 6.5 in the presence of 2 mM myristic acid (substrate). Using synchrotron radiation, both P450BSβ crystals diffracted to 2.5 A resolution. Bijvoet and dispersive anomalous difference Patterson maps show a clear peak corresponding to the haem iron.

Phytanic acid α-hydroxylation by bacterial cytochrome P450

Fatty acid α-hydroxylase, a cytochrome P450 enzyme, from Sphingomonas paucimobilis, utilizes various straight-chain fatty acids as substrates. We investigated whether a recombinant fatty acid α-hydroxylase is able to metabolize phytanic acid, a methyl-branched fatty acid. When phytanic acid was incubated with the recombinant enzyme in the presence of H2O2, a reaction product was detected by gas chromatography, whereas a reaction product was not detected in the absence of H2O2. When a heat-inactivated enzyme was used, a reaction product was not detected with any concentration of H2O2. Analysis of the methylated product by gas chromatography-mass spectrometry revealed a fragmentation pattern of 2-hydroxyphytanic acid methyl ester. By single-ion monitoring, the mass ion and the characteristic fragmentation ions of 2-hydroxyphytanic acid methyl ester were detected at the retention time corresponding to the time of the product observed on the gas chromatogram. The Km value for phytanic acid was approximately 50 μM, which was similar to that for myristic acid, although the calculated Vmax for phytanic acid was about 15-fold lower than that for myristic acid. These results indicate that a bacterial cytochrome P450 is able to oxidize phytanic acid to form 2-hydroxyphytanic acid.

Effect of triton X‐100 and trypsin on NADPH‐cytochromeC reductase reconstitutively active in fatty acid ω‐hydroxylation

In earlier papers [1 ,2] , we reported that a fatty acid ~-hydroxylation system in porcine kidney cortex microsomes was resolved into 2 protein fractions called Fraction I and II, which contained a CO-binding hemoprotein, and NADPH-cytochrome c reductase, respectively. Fraction II was replaced by the corresponding fraction from porcine liver microsomes (liver Fraction II) or spinach ferredoxin-NADP reductase with ferredoxin. Recently, liver Fraction II has been extensively purified. The present paper describes that the purified preparation of liver Fraction II exists in the monodisperse form in the presence of an appropriate concentration of Triton X-100, and that it can be easily transformed into a reconstitutively inactive form, the molecular weight of which is similar to that of trypsinextracted NADPH-cytochrome c reductase.

PURIFICATION AND CHARACTERIZATION OF TWO NEW CYTOCHROME P-450 RELATED TO CYP2C SUBFAMILY FROM RABBIT SMALL INTESTINE MICROSOMES

Two forms of cytochrome P-450, designated P-450id and P-450ie, were purified to specific contents of 14.3 and 15.0 nmol of P-450/mg of protein, respectively, from small intestine mucosa microsomes of rabbits. P-450id and P-450ie showed apparent molecular weights of 50 and 49 kDa, respectively, on SDS-PAGE. Both P-450s catalyzed N-demethylation of nitrosodimethylamine. The NH2-terminal amino acid sequence (first 19 residues) of P-450id exhibited 74-90% identity with those of six members of the rabbit P-450 2C subfamily, except for P-450 2C3. Similarly, the NH2-terminal sequence (first 22 residues) of P-450ie showed 73-86% identity with those of the same members of the rabbit P-450 2C subfamily. The peptide mapping patterns of the two P-450s were quite different from each other. In addition, P-450id did not cross-react with the guinea-pig antibodies against P-450ie. The results indicate that rabbit small intestine mucosa contain two new distinct forms of P-450s, both of which may be classified into the 2C subfamily.

Cell surface expression of immature H glycoprotein in measles virus-infected cells

Two forms of hemagglutinin (H) protein, one with an apparent molecular mass of 78 kDa (78K H protein) and the other with that of 74 kDa (74K H protein), are present in cells infected with measles virus (MV). We previously observed that only the mature 78K H protein, a completely glycosylated form of the 74K H protein, was expressed on the cell surface of the infected cells. In the present study, we detected transient expression of the 74K H protein on the cell surface of infected cells by pulse-chase studies, although the level of this expression was much lower than that of the 78K H protein. On the cell surface the 74K H protein was present as dimers and sensitive to endo-beta-N-acetylglucosaminidase H digestion. Treatment with brefeldin A, which blocks the transport of membrane and secretory proteins from the endoplasmic reticulum to the Golgi apparatus, inhibited the cell surface expression of the 78K H protein, but not that of the 74K H protein. These data suggest that a part of the MV 74K H proteins could be transported directly to the cell surface - probably via an alternative pathway - without processing to the complex form in the Golgi apparatus.

Some properties of a fatty acid ω-hydroxylation system solubilized from liver microsomes

Ichikawa and Yamano [ 1,2] reported that the purified cytochrome P-450 from rabbit liver microsomes was readily reduced by NADPH, ferredoxin-NADP reductase and ferredoxin (spinach electron transport system). However, the activities of aniline hydroxylation and aminopyrine demethylation could not be restored by the reduction of the cytochrome P-450 with such spinach electron transport system. We have recently found that the w-hydroxylation system of medium-chain fatty acids in pig kidney microsomes was resolved into two protein fractions, one of which was replaced by the spinach electron transport system [3] . In the present work, this finding was extended to the fatty acid w-hydroxylation system in rat liver microsomes. In addition, it was found that the treatment of the enzyme preparations with ether resulted in a great decrease of the activity, which could be markedly restored by Triton X-100.