Plasma lipids and blood fluidity in patients with polygenic hypercholesterolaemia treated with fluvastatin

The clinical benefit brought about by HMG-CoA reductase inhibitors (statins) may not entirely be due to their lipid-lowering effect. Further investigation is necessary in order to determine the significance of ancillary effects to the clinical benefit of statin treatment. We studied 27 polygenic hypercholesterolaemia (PHC) patients before and 3 and 6 months after fluvastatin treatment. A control group of 38 normal, sex and age matched, subjects were also studied. The following parameters were measured: haematimetry, serum lipids and general biochemistry, apo-A/B and lipoproteins, fibrinogen, blood filterability, red blood cell aggregation, blood and plasma viscosity. PHC patients showed lower blood filterability (16.00+/-0.99 vs 19.90+/-2.90 microl/s), higher plasma fibrinogen (274.8+/-41.5 vs 241.6+/-43.2 mg/dl), increased erythrocyte aggregation at low shear stress (8.10+/-1.15 vs 7.19+/-1.29) and increased plasma viscosity (1.26+/-0.06 vs 1.23+/-0.05 mPa.s). Notable lipid changes after 6 months fluvastatin treatment were not accompanied by measurable changes in the haemorheological alterations of the PHC patients.

Intracellular distribution of glycogen synthase and glycogen in primary cultured rat hepatocytes

Changes in the intracellular distribution of liver glycogen synthase (GS) might constitute a new regulatory mechanism for the activity of this enzyme at cellular level. Our previous studies indicated that incubation of isolated hepatocytes with glucose activated GS and resulted in its translocation from a homogeneous cytosolic distribution to the cell periphery. These studies also suggested a relationship with insoluble elements of the cytoskeleton, in particular actin. Here we show the translocation of GS in a different experimental model that allows the analysis of this phenomenon in long-term studies. We describe the reversibility of translocation of GS and its effect on glycogen distribution. Incubation of cultured rat hepatocytes with glucose activated GS and triggered its translocation to the hepatocyte periphery. The relative amount of the enzyme concentrated near the plasma membrane increased with time up to 8 h of incubation with glucose, when the glycogen stores reached their maximal value. The lithium-induced covalent activation of GS was not sufficient to cause its translocation to the cell periphery. The intracellular distribution of GS closely resembled that of glycogen. Our results showed an interaction between GS and an insoluble element of the hepatocyte matrix. Although no co-localization between actin filaments and GS was observed in any condition, disruption of actin cytoskeleton resulted in a significantly lower percentage of cells in which the enzyme translocated to the cell periphery in response to glucose. This observation suggests that the microfilament network has a role in the translocation of GS.

Shared control of hepatic glycogen synthesis by glycogen synthase and glucokinase

We have used recombinant adenoviruses (AdCMV-RLGS and AdCMV-GK) to overexpress the liver isoforms of glycogen synthase (GS) and glucokinase (GK) in primary cultured rat hepatocytes. Glucose activated overexpressed GS in a dose-dependent manner and caused the accumulation of larger amounts of glycogen in the AdCMV-RLGS-treated hepatocytes. The concentration of intermediate metabolites of the glycogenic pathway, such as glucose 6-phosphate (Glc-6-P) and UDP-glucose, were not significantly altered. GK overexpression also conferred on the hepatocyte an enhanced capacity to synthesize glycogen in response to glucose, as described previously [Seoane, Gómez-Foix, O'Doherty, Gómez-Ara, Newgard and Guinovart (1996) J. Biol. Chem. 271, 23756-23760], although, in this case, they accumulated Glc-6-P. When GS and GK were simultaneously overexpressed, the accumulation of glycogen was enhanced in comparison with cells overexpressing either GS or GK. Our results are consistent with the hypothesis that liver GS catalyses the rate-limiting step of hepatic glycogen synthesis. However, hepatic glycogen deposition from glucose is submitted to a system of shared control in which the 'controller', GS, is, in turn, controlled by GK. This control is indirectly exerted through Glc-6-P, which 'switches on' GS dephosphorylation and activation.

Identification of two essential glutamic acid residues in glycogen synthase

The detailed catalytic mechanism by which glycosyltransferases catalyze the transfer of a glycosyl residue from a donor sugar to an acceptor is not known. Through the multiple alignment of all known eukaryotic glycogen synthases we have found an invariant 17-amino acid stretch enclosed within the most conserved region of the members of this family. This peptide includes an E-X(7)-E motif, which is highly conserved in four families of retaining glycosyltransferases. Site-directed mutagenesis was performed in human muscle glycogen synthase to analyze the roles of the two conserved Glu residues (Glu-510 and Glu-518) of the motif. Proteins were transiently expressed in COS-1 cells as fusions to green fluorescence protein. The E510A and E518A mutant proteins retained the ability to translocate from the nucleus to the cytosol in response to glucose and to bind to intracellular glycogen. Although the E518A variant had approximately 6% of the catalytic activity shown by the green fluorescence protein-human muscle glycogen synthase fusion protein, the E510A mutation inactivated the enzyme. These results led us to conclude that the E-X(7)-E motif is part of the active site of eukaryotic glycogen synthases and that both conserved Glu residues are involved in catalysis. We propose that Glu-510 may function as the nucleophile and Glu-518 as the general acid/base catalyst.

Intracellular distribution of hepatic glucokinase and glucokinase regulatory protein during the fasted to refed transition in rats

We have studied the intracellular distribution in vivo of glucokinase (GK) and glucokinase regulatory protein (GKRP) in livers of fasted and refed rats, using specific antibodies against both proteins and laser confocal fluorescence microscopy. GK was found predominantly in the nucleus of hepatocytes from starved rats. GK was translocated to the cytoplasm in livers of 1- and 2-h refed animals, but returned to the nucleus after 4 h. GKRP concentrated in the hepatocyte nuclei and its distribution did not change upon refeeding. These results show that, in physiological conditions, GKRP is present predominantly in the nuclei of hepatocytes and that the translocation of hepatic GK from and to the nucleus is operative in vivo.

Glucokinase regulatory protein is essential for the proper subcellular localisation of liver glucokinase

Glucokinase (GK), a key enzyme in the glucose homeostatic responses of the liver, changes its intracellular localisation depending on the metabolic status of the cell. Rat liver GK and Xenopus laevis GK, fused to the green fluorescent protein (GFP), concentrated in the nucleus of cultured rat hepatocytes at low glucose and translocated to the cytoplasm at high glucose. Three mutant forms of Xenopus GK with reduced affinity for GK regulatory protein (GKRP) did not concentrate in the hepatocyte nuclei, even at low glucose. In COS-1 and HeLa cells, a blue fluorescent protein (BFP)-tagged version of rat liver GK was only able to accumulate in the nucleus when it was co-expressed with GKRP-GFP. At low glucose, both proteins concentrated in the nuclear compartment and at high glucose, BFP-GK translocated to the cytosol while GKRP-GFP remained in the nucleus. These findings indicate that the presence of and binding to GKRP are necessary and sufficient for the proper intracellular localisation of GK and directly involve GKRP in the control of the GK subcellular distribution.

Glycogenin, the primer of glycogen synthesis, binds to actin

We have studied the intracellular localization of glycogenin by fusing green fluorescent protein (GFP) to the N-terminus of rabbit muscle glycogenin and expressing the chimeric protein in C2C12, COS-1 and rat hepatic cells. The fusion protein showed a nuclear and cytosolic distribution and partially co-localized with actin in the cytosol. Disruption of the actin cytoskeleton with cytochalasin D led to a change in the pattern of green fluorescence, which coincided with that observed for the remaining non-depolymerized actin. The distribution of the single point mutant K324A was completely uniform and was not affected by this drug. These findings indicate that rabbit muscle glycogenin binds to actin through the heptapeptide 321DNIKKKL327, a common motif found in other actin-binding proteins, which is located at the C-terminal end of this protein, and suggest that the actin cytoskeleton plays an important role in glycogen metabolism.

Muscle glycogen synthase translocates from the cell nucleus to the cystosol in response to glucose

We have studied the intracellular localization of muscular glycogen synthase by fusing the green fluorescent protein (GFP) of the jelly-fish Aequorea victoria to the N-terminus of human muscle glycogen synthase (HMGS), and expressing the chimeric protein in C2C12, COS-1 cells, and primary cultured rat hepatocytes. In contrast to what we have recently found for the hepatic glycogen synthase (Fernandez-Novell et al. (1997) Biochem. J. 321, 227-231), the GFP/HMGS fusion protein is localized to the nucleus of the cell in the absence of glucose, and in the presence of the sugar it is essentially found in the cytosol. Insulin is not required for the translocation of the enzyme.

Identification of a novel bond between a histidine and the essential tyrosine in catalase HPII of Escherichia coli

A bond between the N delta of the imidazole ring of His 392 and the C beta of the essential Tyr 415 has been found in the refined crystal structure at 1.9 A resolution of catalase HPII of Escherichia coli. This novel type of covalent linkage is clearly defined in the electron density map of HPII and is confirmed by matrix-assisted laser desorption/ionization mass spectrometry analysis of tryptic digest mixtures. The geometry of the bond is compatible with both the sp3 hybridization of the C beta atom and the planarity of the imidazole ring. Two mutated variants of HPII active site residues, H128N and N201H, do not contain the His 392-Tyr 415 bond, and their crystal structures show that the imidazole ring of His 392 was rotated, in both cases, by 80 degrees relative to its position in HPII. These mutant forms of HPII are catalytically inactive and do not convert heme b to heme d, suggesting a relationship between the self-catalyzed heme conversion reaction and the formation of the His-Tyr linkage. A model coupling the two processes and involving the reaction of one molecule of H2O2 on the proximal side of the heme with compound 1 is proposed.

Charge reversal of a critical active-site residue of cytochrome-c peroxidase: characterization of the Arg48-->Glu variant

A new variant of cytochrome-c peroxidase in which the positively charged Arg48 present in the distal heme-binding pocket has been replaced with a Glu residue has been prepared and characterized to explore, in part, the possibility that a negative charge close to the heme could contribute to stabilization of a porphyrin-centered pi-cation radical in the compound I derivative of the variant. Between pH 4 and 8, this variant forms three pH-linked spectroscopic species. The electronic absorption and 1H-NMR spectra of the predominant form at low pH (HS1) are indicative of a high-spin, pentacoordinate heme iron system. Near neutral pH, a second high-spin species (HS2) is dominant, in which the heme iron center is hexacoordinated, with a water molecule as the sixth axial ligand. At high pH, the third form (LS) exhibits the spectroscopic characteristics of a low-spin, hexacoordinate heme center with bishistidine axial ligation. The apparent pKa values for these transitions are 4.4 and 7.4, respectively, in phosphate buffers and 5.0 and 7.1, respectively, in phosphate/nitrate buffers. Replacement of Arg48 with Glu reduces the thermal stability of the enzyme and also decreases the Fe(III)/Fe(II) reduction potential of the enzyme by approximately 50 mV relative to that of the wild-type enzyme. The stability of compound I formed by the variant is decreased although the rate at which it forms is just one order of magnitude less than that of the wild-type enzyme, thus confirming previous results which indicate that the function of residue 48 in the wild-type peroxidase is more related to the stability of compound I than to its formation [Erman, J. E., Vitello, L. B., Miller, M. A. & Kraut, J. (1992) J. Am. Chem. Soc. 114, 6592-6593; Vitello, L. B., Erman, J. E., Miller, M. A., Wang, J. & Kraut, J. (1993) Biochemistry 32, 9807-9818]. Stopped-flow studies failed to detect even transient formation of a porphyrin-centered radical following addition of hydrogen peroxide to the Fe(III)-enzyme. The consequences of this drastic electrostatic modification of the active site on the steady-state kinetics of the variant are relatively minor.

Electrostatic modification of the active site of myoglobin: characterization of the proximal Ser92Asp variant

The structural and functional consequences of the introduction of a negatively charged amino acid into the active site of horse heart myoglobin have been investigated by replacement of the proximal Ser92 residue (F7) with an aspartyl residue (Ser92Asp). UV-visible absorption maxima of various ferrous and ferric derivatives and low-temperature EPR spectra of the metaquo (metMb) derivative indicate that the active site coordination geometry has not been perturbed significantly in the variant. 1H-NMR spectroscopy provides direct evidence for the existence of a distal water molecule as the sixth ligand in the oxidized form of the variant at pD 5.7. Spectrophotometric pH titration of the Ser92Asp variant is consistent with this finding and with a pKa = 8.90 +/- 0.02 [25.0 degrees C, mu = 0.10 M (NaCl)] for titration of the distal water molecule, identical to the value reported for the wild-type protein. X-ray crystallography of the metMb derivative indicates that the heme substituents conserve their orientations in the variant protein, except for a slight reorientation of the pyrrole A propionate group to which Ser92 normally hydrogen bonds and reorientation of the carboxyl end of the pyrrole D propionate group. No change is observed in conformation of the proximal (His93) or distal (Wat156) heme ligands. 1H-NMR spectroscopy of the metMbCN form of the protein indicates that a slight rotation of the proximal His93 ligand has occurred in this derivative. Resonance Raman experiments indicate increased conformational heterogeneity in the proximal pocket of the variant. Failure to detect electron density for the Asp residue in the X-ray diffraction map of the variant protein and high average thermal factors for the pyrrole A propionate substituent are consistent with this observation. The variant exhibits novel pH-dependent behavior in the metMb form, as shown by 1H-NMR spectroscopy, and provides evidence for a heme-linked titratable group with a pKa of 5.4 in this derivative. The metMbCN and deoxyMb derivatives also exhibit pH-dependent behavior, with pKas of 5.60 +/- 0.07 and 6.60 +/- 0.07, respectively, compared to the wild-type values of 5.4 +/- 0.04 and 5.8 +/- 0.1. The heme-linked ionizable group is proposed to be His97 in all three derivatives. The reduction potential of the variant is 72 +/- 2 mV vs SHE [25.0 degrees C, mu = 0.10 M (phosphate), pH 6.0], an increase of 8 mV over the wild-type value. The possible influence of a number of variables on the magnitude of the reduction potential in myoglobin and other heme proteins is discussed.

Structure of the heme d of Penicillium vitale and Escherichia coli catalases

A heme d prosthetic group with the configuration of a cis-hydroxychlorin gamma-spirolactone has been found in the crystal structures of Penicillium vitale catalase and Escherichia coli catalase hydroperoxidase II (HPII). The absolute stereochemistry of the two heme d chiral carbon atoms has been shown to be identical. For both catalases the heme d is rotated 180 degrees about the axis defined by the alpha-gamma-meso carbon atoms, with respect to the orientation found for heme b in beef liver catalase. Only six residues in the heme pocket, preserved in P. vitale and HPII, differ from those found in the bovine catalase. In the crystal structure of the inactive N201H variant of HPII catalase the prosthetic group remains as heme b, although its orientation is the same as in the wild type enzyme. These structural results confirm the observation that heme d is formed from protoheme in the interior of the catalase molecule through a self-catalyzed reaction.

pH, electrolyte, and substrate-linked variation in active site structure of the Trp51Ala variant of cytochrome c peroxidase

Electronic absorption, MCD, and 1H NMR spectroscopy have been used to characterize the structures and linkage relationships of three active site states, LS1, HS, and LS2, of the Trp51Ala variant of yeast cytochrome c peroxidase (CcP) in the Fe(III) state. In addition, the binding of three substrates (styrene, catechol, and guaiacol) to the Fe(III) variant has been studied by 1H NMR spectroscopy, and the paramagnetically shifted resonances of the cyanide adduct of the variant have been assigned. The heme iron is hexacoordinated in all three pH-dependent states of the enzyme. LS1, the dominant acidic species, exhibits electronic and MCD spectra indicative of low-spin, bis-histidine coordination environment for the heme iron. The HS form, which dominates at intermediate pH, exhibits electronic, MCD, and 1H NMR spectra characteristic of high-spin heme Fe(III) with axial histidyl and water ligands. The LS2 species exhibits spectroscopic properties indicative of a bis-histidine, low-spin Fe(III) derivative. The equilibrium constants for interconversion of these forms of the variant enzyme are highly dependent on ionic strength, specific anions, and temperature of the solution, with the HS form stabilized relative to the other forms in the presence of several noncoordinating, anionic species. Aromatic substrates such as styrene, catechol, and guaiacol affect the chemical shifts of the heme substituents of the HS species but not of the LS2 species. Based on these results, a model is proposed that accounts to a large extent for the electrostatic origin of the three forms of the active site of the Trp51Ala variant and the mechanisms by which they are differentially stabilized in solution.

Trans effects on cysteine ligation in the proximal His93Cys variant of horse heart myoglobin

Three variants of horse heart myoglobin (Mb) in which the proximal His93 residue has been replaced with a Cys residue have been constructed and studied by NMR, EPR, and MCD spectroscopy to evaluate the contributions of proximal and distal residues to the coordination environment of the heme iron in these proteins. Although no experimental conditions were identified that allowed quantitative ligation of the cysteine residue to the heme iron in the His93Cys variant, all of the spectroscopic evidence collected for the His93Cys/His64Ile and His93Cys/His64Val double variants supports the assignment of thiolate as the ligand to iron in the oxidized forms of these variants. The double metMb variants exhibit Soret maxima that are considerably blue-shifted, 1H NMR spectra with decreased mean methyl resonances, and EPR spectra with highly rhombic g values. These spectroscopic data for the Fe(III) variants resemble the corresponding properties reported for ferricytochrome P-450. The decrease in the reduction potential of the double variants by 280 mV relative to wild-type protein is also consistent with the low midpoint potential of cytochrome P-450. MCD spectroscopy of these variants confirms that the proximal cysteine residue is not bound in the reduced forms of these proteins and, in the case of the His93Cys variant, that the distal histidine is coordinated to the iron. Similar coordination environments were created in the ferrimyoglobin variants by cyanogen bromide modification, which resulted in cyanation of the sulfur atom and prevented the ligation of Cys93 to the heme iron.(ABSTRACT TRUNCATED AT 250 WORDS)

The proximal ligand variant His93Tyr of horse heart myoglobin

The spectroscopic and structural properties of the His93Tyr variant of horse heart myoglobin have been studied to assess the effects of replacing the proximal His residue of this protein with a tyrosyl residue as occurs in catalases from various sources. The variant in the ferric form exhibits electronic spectra that are independent of pH between pH 7 and 10, and it exhibits changes in absorption maxima and intensity that are consistent with a five-coordinate heme iron center at the active site. The EPR spectrum of the variant is that of a high-spin, rhombic system similar to that reported for bovine liver catalase. The 1D 1H-NMR spectrum of the variant confirms the five-coordinate nature of the heme iron center and exhibits a broad resonance at 112.5 ppm that is attributable to the meta protons of the phenolate ligand. This result indicates that the new Tyr ligand flips at a significant rate in this protein. The thermal stability of the Fe(III) derivative is unchanged from that of the wild-type protein (pH 8) while the midpoint reduction potential [-208 mV vs SHE (pH 8.0, 25 degrees C)] is about 250 mV lower. The three-dimensional structure of the variant determined by X-ray diffraction analysis confirms the five-coordinate nature of the heme iron center and establishes that the introduction of a proximal Tyr ligand is accommodated by a shift of the F helix (residues 88-99) in which this residue resides away from the heme pocket. Additional effects of this change are small shifts in the positions of Leu29, a heme propionate, and a heme vinyl group that are accompanied by altered hydrogen bonding interactions with the heme prosthetic group.(ABSTRACT TRUNCATED AT 250 WORDS)

Proton linkage in formation of the cytochrome c-cytochrome c peroxidase complex: electrostatic properties of the high- and low-affinity cytochrome binding sites on the peroxidase

The electrostatic character of cytochrome c-cytochrome c peroxidase complex formation has been studied by potentiometric titration between pH 5.5 and 7.75. Potentiometric data obtained at ionic strength > or = 100 mM were adequately analyzed in terms of 1:1 complex formation while the simplest model capable of fitting similar data obtained at lower ionic strength involves the assumption of two inequivalent binding sites for the cytochrome on the peroxidase. The stability of cytochrome c binding at the high-affinity site is ca. three orders of magnitude greater than that observed for the low-affinity site and is optimal between pH 6.75 and 7. The electrostatic properties of the two binding sites are distinctly different because, at most values of pH, binding of cytochrome c to the high-affinity site results in proton release while binding of the cytochrome to the low-affinity site results in proton uptake. Furthermore, binding of the cytochrome to the low-affinity site appears to be least stable in the pH range where binding to the high-affinity site is optimal. Interestingly, the binding parameters derived from these measurements were independent of temperature, consistent with a substantial entropic contribution to complex stability. Ferricytochrome c binds to the peroxidase with a slightly greater affinity than does ferrocytochrome c, and no evidence for specific anion effects on complex stability was observed. At low ionic strength (< or = 50 mM) and high pH (7.75), the interaction of the two proteins is more complex and cannot be adequately analyzed in terms of the two-site model.

Recombinant human erythrocyte cytochrome b5

The gene encoding the human erythrocyte form of cytochrome b5 (97 residues in length) has been prepared by mutagenesis of an expression vector encoding lipase-solubilized bovine liver microsomal cytochrome b5 (93 residues in length) (Funk et al., 1990). Efficient expression of this gene in Escherichia coli has provided the first opportunity to obtain this protein in quantities sufficient for physical and functional characterization. Comparison of the erythrocytic cytochrome with the trypsin-solubilized bovine liver cytochrome b5 by potentiometric titration indicates that the principal electrostatic difference between the two proteins results from two additional His residues present in the human erythrocytic protein. The midpoint reduction potential of this protein determined by direct electrochemistry is -9 +/- 2 mV vs SHE at pH 7.0 (mu = 0.10 M, 25.0 degrees C), and this value varies with pH in a fashion that is consistent with the presence of a single ionizable group that changes pKa from 6.0 +/- 0.1 in the ferricytochrome to 6.3 +/- 0.1 in the ferrocytochrome with delta H degrees = -3.2 +/- 0.1 kcal/mol and delta S degrees = -11.5 +/- 0.3 eu (pH 7.0, mu = 0.10). The 1D 1H NMR spectrum of the erythrocytic ferricytochrome indicates that 90% of the protein binds heme in the "major" orientation and 10% of the protein binds heme in the "minor" orientation (pH 7.0, 25 degrees C) with delta H degrees = -2.9 +/- 0.3 kcal/mol and delta S degrees = -5.4 +/- 0.9 eu for this equilibrium.

Active site coordination chemistry of the cytochrome c peroxidase Asp235Ala variant: spectroscopic and functional characterization

Asp235 in yeast cytochrome c peroxidase forms a hydrogen bond with His175, the proximal histidyl residue, that has been suggested to be important in determining the electronic properties of the heme iron and that may be involved in stabilizing the higher oxidation states of the peroxidase that form transiently during catalysis. The current study employs 1H and 15N-NMR spectroscopy to study the electronic properties of and the effects of pH on the active site of the Asp235Ala variant. This variant exhibits three spectroscopic species between pH 5 and 9: a high-spin species that forms at low pH and two low-spin species that form successively at higher pH. Nevertheless, the activity of the variant exhibits a pH dependence virtually identical to that of the wild-type protein, though the activity of the variant is 3 orders of magnitude lower at all values of pH between pH 5 and 8.5. These findings suggest that the spin state and coordination environment of the heme iron in cytochrome c peroxidase do not dictate the rate of substrate (cytochrome c) oxidation. Binding of cyanide to the variant enzyme results in formation of a single species as detected by NMR spectroscopy. Analysis of high-resolution 1D and 2D 1H-NMR and 15N-NMR spectra of the cyanide adduct has permitted characterization of the properties of this derivative and the strength of the proximal ligand bond to the heme iron. Disruption of the hydrogen bond between the proximal histidine and Asp235 that exists in the wild-type enzyme dramatically reduces the strength of the interaction between the proximal ligand and the iron; this effect combined with concurrent changes in the distal heme-binding pocket accounts for the increase in reduction potential reported for the Fe3+/Fe2+ couple. The catalytic consequences of the structural and electronic properties of the variant elucidated in this study are discussed.

Transmutation of a heme protein

Residue Asn57 of bovine liver cytochrome b5 has been replaced with a cysteine residue, and the resulting variant has been isolated from recombinant Escherichia coli as a mixture of four major species: A, BI, BII, and C. A combination of electronic spectroscopy, 1H NMR spectroscopy, resonance Raman spectroscopy, electrospray mass spectrometry, and direct electrochemistry has been used to characterize these four major cytochrome derivatives. The red form A (E(m) = -19 mV) is found to possess a heme group bound covalently through a thioether linkage involving Cys57 and the alpha carbon of the heme 4-vinyl group. Form BI has a covalently bound heme group coupled through a thioether linkage involving the beta carbon of the heme 4-vinyl group. Form BII is similar to BI except that the sulfur involved in the thioether linkage is oxidized to a sulfoxide. The green form C (E(m) = 175 mV) possesses a noncovalently bound prosthetic group with spectroscopic properties characteristic of a chlorin. A mechanism is proposed for the generation of these derivatives, and the implications of these observations for the biosynthesis of cytochrome c and naturally occurring chlorin prosthetic groups are discussed.

Monooxygenase activity of cytochrome c peroxidase

Recombinant cytochrome c peroxidase (CcP) and a W51A mutant of CcP, in contrast to other classical peroxidases, react with phenylhydrazine to give sigma-bonded phenyl-iron complexes. The conclusion that the heme iron is accessible to substrates is supported by the observation that CcP and W51A CcP oxidize thioanisole to the racemic sulfoxide with quantitative incorporation of oxygen from H2O2. Definitive evidence for an open active site is provided by stereoselective epoxidation by both enzymes of styrene, cis-beta-methylstyrene, and trans-beta-methylstyrene. trans-beta-methylstyrene yields exclusively the trans-epoxide, but styrene yields the epoxide and phenylacetaldehyde, and cis-beta-methylstyrene yields both the cis- and trans-epoxides and 1-phenyl-2-propanone. The sulfoxide, stereoretentive epoxides, and 1-phenyl-2-propanone are formed by ferryl oxygen transfer mechanisms because their oxygen atom derives from H2O2. In contrast, the oxygen in the trans-epoxide from the cis-olefin derives primarily from molecular oxygen and is probably introduced by a protein cooxidation mechanism. cis-[1,2-2H]-1-Phenyl-1-propene is oxidized to [1,1-2H]-1-phenyl-2-propanone without a detectable isotope effect on the epoxide:ketone product ratio. The phenyl-iron complex is not formed and substrate oxidation is not observed when the prosthetic group is replaced by delta-meso-ethylheme. CcP thus has a sufficiently open active site to form a phenyl-iron complex, to oxidize thioanisole to the sulfoxide, and to epoxidize styrene and beta-methylstyrene. The results indicate that a ferryl (Fe(IV) = O)/protein radical pair can be coupled to achieve two-electron oxidations. The unique ability of CcP to catalyze monooxygenation reactions does not conflict with its peroxidase function because cytochrome c is oxidized at a distinct surface site (DePillis, G. D., Sishta, B. P., Mauk, A. G., and Ortiz de Montellano, P. R. (1991) J. Biol. Chem. 266, 19334-19341).

Recombinant cytochrome c peroxidase folds properly without conformational "annealing"

Recombinant cytochrome c peroxidase isolated from Escherichia coli has recently been reported to exhibit an abnormal electronic absorption spectrum that is converted to the normal spectrum after conformational "annealing" of the recombinant enzyme by passage over a cytochrome c affinity column. The current report provides evidence that the abnormal spectrum observed in some preparations of recombinant cytochrome c peroxidase arises from the presence of contaminant, damaged forms cytochrome c peroxidase with altered spectra. Removal of these contaminant forms produces a major cytochrome c peroxidase fraction with a normal spectrum. We conclude that elution of recombinant cytochrome c peroxidase over a cytochrome c affinity column does not produce normal enzyme through conformational "annealing" but that it produces purified enzyme through removal of contaminants.

Microbiologic oxidation of estratrienes and estratetraenes by Streptomyces roseochromogenes ATCC 13400

Incubation of estrone (1a) with Streptomyces roseochromogenes ATCC 13400 yielded a mixture of 3,16 alpha-dihydroxyestra-1,3,5(10)-trien-17-one (3a) and 3,17 beta-dihydroxyestra-1,3,5(10)-trien-16-one (4a). Transformation of 3-methoxyestra-1,3,5(10)-trien-17-one (1b), 3-hydroxyestra-1,3,5(10),9(11)-tetraen-17-one (2a), and 3-methoxyestra-1,3,5(10),9(11)-tetraen-17-one (2b) with the same microorganism gave the corresponding mixtures of 16 alpha-hydroxy-17-ketones and 17 beta-hydroxy-16-ketones (3b and 4b, 6a and 7a, 6b and 7b, respectively). In addition, in these three last experiments, the 16 beta-17 beta-dihydroxy derivatives 5b, 8a, and 8b, respectively, were also isolated. The complete assignments of the 13C nuclear magnetic resonance spectra of these compounds are given.