The Roles of Putidaredoxin and P450cam in Methylene Hydroxylation

The steroid-9 alpha-hydroxylation system from Nocardia species

The steroid 9 alpha-hydroxylase from Nocardia species M117 was found to be an electron-transport chain consisting of an NADH-dependent flavoprotein reductase and two iron-sulfur proteins named protein II and protein III. The components were partially purified. The flavoprotein reductase from Nocardia species M117 was enriched 20-fold to 100 units/mg and protein III 200-fold to 2400 units/mg protein. Protein II has a molecular weight of approximately 214 000. The purification factor of protein II was not determined. The absorption spectrum of protein II shows a maximum at 425 nm in the oxidized form and maxima at 510 nm, 415 nm and 370 nm in the reduced state; whereas protein III has a prominent maximum at 452 nm in the oxidized form and no absorption maximum in the reduced state. Carbon monoxide treatment of the reduced forms of protein II and protein III showed no maximum at 450 nm. Both proteins II and III are sensitive to oxygen. The hydroxylase activity can be reconstituted from the isolated components. Activity of the combined proteins was demonstrated by product analysis and NADH consumption produced by the addition of progesterone. Protein III catalyzes the reduction of cytochrome c in the presence of NADH and Nocardia flavoprotein reductase. The reconstitution of hydroxylase activity from cytochrome-free enzyme preparations excludes the participation of cytochrome P-450 in this steroid hydroxylase system.

Accumulation of 6-deoxyerythronolide B in a normal strain of Streptomyces erythreus and hydroxylation at carbon 6 of the erythranolide ring system by a soluble noninduced cell-free enzyme system

Erythronolide B, a presumed intermediate in the biosynthesis of the erythromycins, has been shown to be formed from 6-deoxyerythronolide B by hydroxylation at C-6. The substrate, a metabolite of a blocked mutant of Streptomyces erythreus and postulated to be an intermediate in the biosynthesis of the erythromycins, is found also in wild-type cultures of S. erythreus CA340 either normally or in increased amount when an inhibitor of NADPH function is present. The hydroxylation of 6-deoxyerythronolide B is catalyzed by a stable and soluble cell-free enzyme preparation obtained from noninduced S. erythreus CA340, and the maximal specific activity of the hydroxylase system is found with the protein fraction precipitating between 50% and 90% of saturation with ammonium sulfate. The hydroxylase activity correlates well with the specific content of a cytochrome P-450 moiety present in the system and is inhibited by anaerobiosis and carbon monoxide.

The iron-sulphur centres of soluble hydrogenase from Alcaligenes eutrophus

The soluble hydrogenase (hydrogen:NAD+ oxidoreductase (EC 1.12.1.2) from Alcaligenes eutrophus has been purified to homogeneity by an improved procedure, which includes preparative electrophoresis as final step. The specific activity of 57 mumol H2 oxidized/min per mg protein was achieved and the yield of pure enzyme from 200 g cells (wet weight) was about 16 mg/purification. After removal of non-functional iron, analysis of iron and acid-labile sulphur yielded average values of 11.5 and 12.9 atoms/molecule of enzyme, respectively. p-Chloromercuribenzoate was a strong inhibitor of hydrogenase and apparently competed with NAD not with H2. Chelating agents, CO and O2 failed to inhibit enzyme activity. The oxidized hydrogenase showed an EPR spectrum with a small signal at g = 2.02. On reduction the appearance of a high temperature (50--77 K) signal at g = 2.04, 1.95 and a more complex low temperature (less than 30 K) spectrum at g = 2.04, 2.0, 1.95, 1.93, 1.86 was observed. The pronounced temperature dependence and characteristic lineshape of the signals obtained with hydrogenase in 80--85% dimethylsulphoxide demonstrated that iron-sulphur centres of both the [2Fe-2S] and [4Fe-4S] types are present in the enzyme. Quantitation of the EPR signals indicated the existence of two identical centres each of the [4Fe-4S] and of the [2Fe-2S] type. The midpoint redox potentials of the [4Fe-4S] and the [2Fe-2S] centres were determined to be -445 mV and -325 mV, respectively. Spin coupling between two centres, indicated by the split feature of the low temperature spectrum of the native hydrogenase around g = 1.95, 1.93, has been established by power saturation studies. On reduction of the [Fe-4S] centres, the electron spin relaxation rate of the [2Fe-2S] centres was considerably increased. Treatment of hydrogenase with CO caused no change in EPR spectra.

The drug metabolism systems of liver and liver tumors: a comparison of activities and characteristics

Transplantable rat liver tumors 5123 t.c., 7288 ct.c., 5123 t.c.(H) and the Novikoff hepatoma have active mixed function oxidase systems capable of metabolizing a variety of drug and polycyclic hydrocarbon substrates. The tumor drug metabolism systems are at best 20% as active as rat liver. The tumor drug metabolism activities are induced by pretreatment with phenobarbital or beta-naphthoflavone and can be inhibited with specific inhibitors such as carbon monoxide or 7,8-benzoflavone. Tumor drug metabolism systems appear to consist of cytochrome P-450 and cytochrome P-450 reductase. The properties of the two protein components from tumors are highly similar to the corresponding components of the liver drug metabolism system. Cytochrome P-450 reductase has been at least partially purified from the Novikoff hepatoma and hepatoma 5123 t.c.(H). The kinetic and physical properties of the tumor reductases are similar to those of the liver reductase except that the Km of hepatoma 5123 t.c.(H) reductase, but not of the Novikoff hepatoma reductase for NADPH, is elevated an order of magnitude over the Km of the liver reductase. The mechanism for the interaction of electron donor and electron acceptor with liver or tumor reductases seems to be a sequential reaction mechanism. Experiments on the NADP-inhibition of the interaction of NADPH and cytochrome c with liver reductase indicate that NADP is competitive with NADPH and noncompetitive with cytochrome c. This result is consistent with the postulate of a sequential reaction for NADPH-cytochrome P-450 reductases of liver and tumors. These data support the conclusions that an active drug metabolism system is present in liver tumors and that the tumor systems are constituted like the liver system.

Magnetic circular dichroism of Pseudomonas putida cytochrome P-450 in near infrared region

Magnetic circular dichroism spectra of oxidized, reduced and carbonmonoxy reduced forms of cytochrome P-450 from D-camphor grown Pseudomonas putida (P-450cam) were studied in the near infrared region (650 to 1200 nm) at various temperatures in the presence of D-camphor. Oxidized P-450cam with camphor exhibited positive (+) and negative (-) magnetic CD bands at 825 and 970 nm, respectively, and both of them were assigned to Faraday B terms. The magnetic CD spectrum of reduced P-450cam in the presence of D-camphor exhibited at least five components in the region between 650 to 1175 nm and one of them at 760 nm showed considerably smaller magnitude than that of the corresponding band of deoxymyoglobin. These results were interpreted to mean that the heme-iron in both oxidized and reduced P-450cam has a ligand field symmetry lower than C4v, i.e. a strong rhombic character of the heme in cytochrome P-450. Carbonmonoxide complex of reduced P-450cam exhibited no detectable magnitude of magnetic CD in the near infrared region but showed CD bands at 710 (-) and 850 (+) nm. The results were compared and discussed with those of carbonmonoxy hemoglobin and myoglobin. In addition, temperature dependent changes in the spin state of oxidized P-450cam from high to low by decrease of temperature were observed by measuring both magnetic CD and absorption spectra in the near ultraviolet and visible regions (300 to 650 nm), provided that the temperature of the sample was varied slowly (approximately 3 degrees C/min) between room and liquid nitrogen temperature in a 0.03 M phosphate buffer (pH 7.2) containing a saturated amount of D-camphor and 70% (v/v) glycerol. The significance of this phenomenon is also discussed.

Electron paramagnetic resonance studies of cytochrome P-450 and adrenal ferredoxin in single whole rat adrenal glands. Effect of corticotropin

Low and high spin ferric cytochrome P-450 and reduced adrenal ferredoxin (adrenodoxin) have been directly studied by EPR techniques in whole rat adrenal glands. The spectra obtained correspond closely to those obtained from sub-cellular fractions except in the case of low spin ferric cytochrome P-450, where there are differences in the shape of the g = 2.41 line. The relative magnitudes of these peaks in anaerobic and aerobic rapidly frozen adrenals from control and corticotropin stimulated hypophysectomised rats were used to investigate the control and rate limiting steps in adrenal steroid biosynthesis via cytochrome P-450. All adrenals showed a close to maximal level of reduced adrenodoxin and aerobic and anaerobic glands from control rats and aerobic glands from corticotropin stimulated rats showed similar quantities of low spin ferric cytochrome P-450. On anaerobiosis the quantity of low spin ferric cytochrome in adrenals from corticotropin stimulated rats dropped to 30--40% of the aerobic level. Treatment of the rats with cycloheximide prior to administration of corticotropin prevented these changes. Approximately 0.4% of the total cytochrome P-450 was high spin ferric in control adrenals and in aerobic stimulated adrenals this rose to approximately to 0.6%. These results demonstrate that association of substrate with cytochrome P-450 is the rate limiting step in adrenal steroidogenesis via cytochrome P-450. It is suggested on the basis of these and mitochondrial optical and EPR experiments that the limiting step being observed is cholesterol binding to cholesterol side chain cleavage cytochrome P-450, and that the rate of this association is stimulated by corticotropin.

[Hydrocarbon metabolism in a marine bacterium]

The marine bacterium L.16.1 (Alcaligenes sp.) grows preferentially on alkanes (C10 to C18) with a very high growth yield (98 per cent); optimal growth depends strictly on the presence of a well-defined NaCl concentration (100 mM). Our strain is constitutive for the enzymatic systems responsible for the oxidation of alkanes to fatty acids, i.e. NADH-dependent hydroxylase, alcohol and aldehyde dehydrogenases, the latter of which located at the cytoplasmic membrane level. The aerobic oxidation of primary alcohols by particulate extracts prepared in the presence of 400 mM NaCl is NAD+-dependent (Km = 0.082 mM, Vmax = 238 with decanol). With extracts prepared in the absence of NaCl, Vmax undergoes a very strong decrease. On the contrary , the NAD+ (P)+-dependent oxidation of aldehydes is carried out anaerobically by the same extracts irrespective of the presence or the absence of added Na+ in the solutions used for the preparation of these extracts. A possible explanation for our results could be that Na+ acts on the enzymatic systems for which the maintenance of the membrane integrity is essential. This interpretation is consistent with the slowing down of the growth speed accompanying the decrease of NaCl concentration in the growth medium. With regard to alcohol and aldehyde-dehydrogenases, it is noteworthy that these enzymes behave like similar enzymatic activities induced by alkanes in other microorganisms.

A 4-methoxybenzoate O-demethylase from Pseudomonas putida. A new type of monooxygenase system

A strain of Pseudomonas putida grown on 4-methoxybenzoate as sole carbon source contains an enzyme system for the O-demethylation of this substrate. The enzyme system is purifiable and can be separated into two components: an NADH-dependent reductase and an iron-containing and acid-labile-sulfur-containing monooxygenase. The reductase, of molecular weight 42000 and containing two chromophores, an FMN and an iron-sulfur complex (EPR at g = 1.95), reduces both one-electron and two-electron acceptors (i.e., ferricyanide, 2,6-dichloroindophenol, cytochrome c, and cytochrome b5) at an optimum pH of 8.0. Increasing ionic strength affects these activities differently. The absolute spectrum of the oxidized displays distinct absorption peaks at 409 and 463 nm and a small shoulder between 538 and 554 nm. Treatment with dithionite or NADH reduces the absorbance throughout the visible range, yielding a spectrum with small maxima at 402 and 538 nm. Spectroscopic characteristics of the reductase indicate a tight coupling between its two chromophores. The iron-containing and acid-labile-sulfur-containing monooxygenase, which has a molecular weight of about 120000, contains an iron-sulfur chromophore with an EPR signal at g = 1.90. This protein is a dimer whose subunits each have a molecular weight of about 50000 and are perhaps identical. The optical absorption properties are somewhat unusual. In contrast to other iron-sulfur proteins, there is no significant peak near 415 nm in the absorption spectrum of the oxidized protein, but rather one at 455 nm. The presence of the substrate 4-methoxybenzoate increases both the NADH-dependent reductase. Hydroxylation can be achieved by the monooxygenase also in absence of the reductase with artifical reductants. This enzyme opens a new group of oxygenases within the classification scheme, i.e., iron-containing and labile-sulfur-containing monooxygenases. From the reported data, a scheme for the interaction of the isolated pigments and their relationship to various acceptors is proposed.

On the structure of putidaredoxin and cytochrome P-450 cam and their mode of interaction

Structural and immunochemical experiments with putidaredoxin, cytochrome P-450cam, and their 1:1 complex have led us to the following conclusions: Despite the remarkable sequence homology between putidaredoxin and adrenodoxin which permits a tentative assignment of cysteines binding to the (Fe-S)2 prosthetic group, these redox proteins cannot replace each other in reconstitution experiments because putidaredoxin contains a disulfide loop close to its P-450cam binding site. This feature may also be responsible for the complete lack of immunochemical cross reactivity between these proteins. The stability of putidaredoxin can be enhanced significantly by cross linkage with glutaraldehyde without change in spectral, catalytic, or immunochemical properties, Putidaredoxin also gains stability by binding to the P-450-camphor complex in a 1:1 ratio. Precipitation of this complex with anti-P-450cam antibodies gives access to site specific antibodies directed against the putidaredoxin binding site of P-450cam. A series of putidaredoxin-cytochrome P-450cam-substrate complexes with ratios of 1 to 6 molecules of redoxin per molecule of cytochrome have been obtained by migration of excess redoxin across prefocused P-450cam in electrofocusing. Complete inhibition of camphor hydroxylation was achieved by anti-P-450cam antibodies, their Fab fragments, anti-putidaredoxin-trimer antibodies, and antibodies directed against the putidaredoxin-P-450cam complex. Five major antigenic sites were tentatively established for P-450cam, two of which seem to be associated with the BrCN hemepeptide while one each relates to the putidaredoxin binding site, the Trp-Arg site close to the C-terminus, and the site surrounding the most reactive SH group which gives rise to dimer formation. Iodination, of P-450cam at tyrosyl residues only permitted use of a sensitive radioimmunoassay procedure for testing of cross reacting material (CRM) remaining after degradation of P-450cam with BrCN and enzymes, denaturation with acetone, and complex formation with the redoxin. The BrCN hemepeptide still has a Soret maximum at 390 nm and reacts with CO yielding a P-420 spectrum. All 6 half-cystines of P-450cam are present as free sulfhydryls and can be titrated after denaturation but only 4 of them are available in the P-450-camphor complex. Three of these are close to each other and the heme, and work in concert; their alkylation with N-ethyl maleimide (NEM) leads to shifts of the Soret from 391 to 417 nm and concomitant changes in redox potential, EPR-signals and DPNH-reactivity. The fifth SH group is protected by camphor while the 6th SH group, still present in the BrCN heme-peptide, is implicated in chelation to the heme iron by a drastic change in EPR spectra, reflecting pure axial symmetry at the heme after complete alkylation by NEM.