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1.
Background
Membrane-associated progesterone receptors (MAPRs) are thought to mediate a number of rapid cellular effects not involving changes in gene expression. They do not show sequence similarity to any of the classical steroid receptors. We were interested in identifying distant homologs of MAPR better to understand their biological roles.Results
We have identified MAPRs as distant homologs of cytochrome b 5. We have also found regions homologous to cytochrome b 5 in the mammalian HERC2 ubiquitin transferase proteins and a number of fungal chitin synthases.Conclusions
In view of these findings, we propose that the heme-binding cytochrome b 5 domain served as a template for the evolution of membrane-associated binding pockets for non-heme ligands. 相似文献2.
Jan Pyrih Karel Harant Eva Martincová Robert Sutak Emmanuel Lesuisse Ivan Hrdy Jan Tachezy 《Eukaryotic cell》2014,13(2):231-239
The anaerobic intestinal pathogen Giardia intestinalis does not possess enzymes for heme synthesis, and it also lacks the typical set of hemoproteins that are involved in mitochondrial respiration and cellular oxygen stress management. Nevertheless, G. intestinalis may require heme for the function of particular hemoproteins, such as cytochrome b5 (cytb5). We have analyzed the sequences of eukaryotic cytb5 proteins and identified three distinct cytb5 groups: group I, which consists of C-tail membrane-anchored cytb5 proteins; group II, which includes soluble cytb5 proteins; and group III, which comprises the fungal cytb5 proteins. The majority of eukaryotes possess both group I and II cytb5 proteins, whereas three Giardia paralogs belong to group II. We have identified a fourth Giardia cytb5 paralog (gCYTb5-IV) that is rather divergent and possesses an unusual 134-residue N-terminal extension. Recombinant Giardia cytb5 proteins, including gCYTb5-IV, were expressed in Escherichia coli and exhibited characteristic UV-visible spectra that corresponded to heme-loaded cytb5 proteins. The expression of the recombinant gCYTb5-IV in G. intestinalis resulted in the increased import of extracellular heme and its incorporation into the protein, whereas this effect was not observed when gCYTb5-IV containing a mutated heme-binding site was expressed. The electrons for Giardia cytb5 proteins may be provided by the NADPH-dependent Tah18-like oxidoreductase GiOR-1. Therefore, GiOR-1 and cytb5 may constitute a novel redox system in G. intestinalis. To our knowledge, G. intestinalis is the first anaerobic eukaryote in which the presence of heme has been directly demonstrated. 相似文献
3.
To understand the role of the structural elements of cytochrome b 5 in its interaction with cytochrome P450 and the catalysis performed by this heme protein, we carried out comparative structural and functional analysis of the two major mammalian forms of membrane-bound cytochrome b 5 — microsomal and mitochondrial, designed chimeric forms of the heme proteins in which the hydrophilic domain of one heme protein is replaced by the hydrophilic domain of another one, and investigated the effect of the highly purified native and chimeric heme proteins on the enzymatic activity of recombinant cytochromes P4503A4 and P45017A1 (CYP3A4 and CYP17A1). We show that the presence of a hydrophobic domain in the structure of cytochrome b 5 is necessary for its effective interaction with its redox partners, while the nature of the hydrophobic domain has no significant effect on the ability of cytochrome b 5 to stimulate the activity of cytochrome P450-catalyzed reactions. Thus, the functional properties of cytochrome b 5 are mainly determined by the structure of the hemebinding domain. 相似文献
4.
Emma L. Reid Karen D. Weynberg John Love Michail N. Isupov Jennifer A. Littlechild William H. Wilson Steven L. Kelly David C. Lamb Michael J. Allen 《FEBS letters》2013
Cytochrome b5 is a ubiquitous electron transport protein. The sequenced viral OtV-2 genome, which infects Ostreococcus tauri, was predicted to encode a putative cytochrome b5 enzyme. Using purified OtV-2 cytochrome b5 we confirm this protein has identical spectral properties to purified human cytochrome b5 and additionally that the viral enzyme can substitute for yeast cytochrome b5 in yeast cytochrome P450 51 mediated sterol 14α-demethylation. The crystal structure of the OtV-2 cytochrome b5 enzyme reveals a single domain, comprising four β sheets, four α helices and a haem moiety, which is similar to that found in larger eukaryotic cytochrome proteins. As a product of a horizontal gene transfer event involving a subdomain of the host fumarate reductase-like protein, OtV-2 cytochrome b5 appears to have diverged in function and is likely to have evolved an entirely new role for the virus during infection. Indeed, lacking a hydrophobic C-terminal anchor, OtV-2 encodes the first cytosolic cytochrome b5 characterised. The lack of requirement for membrane attachment (in contrast to all other microsomal cytochrome b5s) may be a reflection of the small size of the host cell, further emphasizes the unique nature of this virus gene product and draws attention to the potential importance of cytochrome b5 metabolic activity at the extremes of cellular scale. 相似文献
5.
Cytochrome proteins perform a broad spectrum of biological functions ranging from oxidative metabolism to electron transport and are thus essential to all organisms. The b-type cytochrome proteins bind heme noncovalently, are expressed in many different forms and are localized to various cellular compartments. We report the characterization of the cytochrome b5 (Cyt-b) gene of Drosophila virilis and compare its structure to the Cyt-b gene of Drosophila melanogaster. As in D. melanogaster, the D. virilis gene is nuclear encoded and single copy. Although the intron/exon structures of these homologues differ, the Cyt-b proteins of D. melanogaster and D. virilis are approximately 75% identical and share the same size coding regions (1,242 nucleotides) and protein products (414 amino acids). The Drosophila Cyt-b proteins show sequence similarity to other b-type cytochromes, especially in the N-terminal heme-binding domain, and may be targeted to the mitochondrial membrane. The greatest levels of similarity are observed in areas of potential importance for protein structure and function. The exon sequences of the D. virilis Cyt-b gene differ by a total of 292 base changes. However, 62% of these changes are silent. The high degree of conservation between species separated by 60 million years of evolution in both the DNA and amino acid sequences suggests this nuclear cytochrome b5 locus encodes an essential product of the Drosophila system.Correspondence to: C.E. Rozek 相似文献
6.
Immunochemical evidence for the participation of cytochrome b5 in microsomal stearyl-CoA desaturation reaction 总被引:2,自引:0,他引:2
A rabbit antiserum was prepared against rat liver microsomal cytochrome b5, and utilized in demonstrating the participation of this cytochrome in the microsomal stearyl-CoA desaturation reaction. The antiserum inhibited the NADH-cytochrome c reductase activity of rat liver microsorncs, but it did not inhibit either NADH-ferricyanide or NADPH-cytochrome c reductase activity of the microsomes. Thus, the inhibitory effect of the antiserum on the microsomal electron-transferring reactions seemed to be specific to those which require the participation of cytochrome b5.The NADH-dependent and NADPH-dependent desaturations of stearyl CoA by rat liver microsomes were strongly inhibited by the antiserum. The reduction of cytochrome b5 by NADH-cytochrome b5 reductase as well as the reoxidation of the reduced cytochrome b3 by the desaturase, the terminal cyanide-sensitive factor of the desaturation system, was also strongly inhibited by the antiserum. When about 90%, of cytochrome b5 was removed from rat liver microsomes by protease treatment, the desaturation activity of the microsomes became much more sensitive to inhibition by the antiserum. These results confirmed our previous conclusion that the reducing equivalent for the desaturation reaction is transferred from NAD(P)H to the cyanidesensitive factor mainly via cytochrome b5 in the microsomal membranes. 相似文献
7.
Stéphane T. Gabilly Beth Welty Dreyfuss Mohamed Karamoko Vincent Corvest Janette Kropat M. Dudley Page Sabeeha S. Merchant Patrice P. Hamel 《The Journal of biological chemistry》2010,285(39):29738-29749
The c-type cytochromes are metalloproteins with a heme molecule covalently linked to the sulfhydryls of a CXXCH heme-binding site. In plastids, at least six assembly factors are required for heme attachment to the apo-forms of cytochrome f and cytochrome c6 in the thylakoid lumen. CCS5, controlling plastid cytochrome c assembly, was identified through insertional mutagenesis in the unicellular green alga Chlamydomonas reinhardtii. The complementing gene encodes a protein with similarity to Arabidopsis thaliana HCF164, which is a thylakoid membrane-anchored protein with a lumen-facing thioredoxin-like domain. HCF164 is required for cytochrome b6f biogenesis, but its activity and site of action in the assembly process has so far remained undeciphered. We show that CCS5 is a component of a trans-thylakoid redox pathway and operates by reducing the CXXCH heme-binding site of apocytochrome c prior to the heme ligation reaction. The proposal is based on the following findings: 1) the ccs5 mutant is rescued by exogenous thiols; 2) CCS5 interacts with apocytochrome f and c6 in a yeast two-hybrid assay; and 3) recombinant CCS5 is able to reduce a disulfide in the CXXCH heme-binding site of apocytochrome f. 相似文献
8.
M. M. Marchenko O. V. Ketsa 《Biochemistry (Moscow) Supplemental Series B: Biomedical Chemistry》2012,6(4):322-328
The activity of liver microsomal and Guerin??s carcinoma NADH-cytochrome b 5 reductase, the content and the rate of cytochrome b 5 oxidation-reduction have been investigated in tumor-bearing rats exposed to preliminary irradiation. Preliminary irradiation of rats (before transplantation of Guerin??s carcinoma) resulted in the decrease of NADH-cytochrome b 5 reductase activity and the content of cytochrome b 5 in the Guerin??s carcinoma microsomal fraction in the latent and logarithmic phases of oncogenesis compared with the non-irradiated tumor-bearing rats. The effect of irradiation preceding transplantation of the tumor to rats results in the increase of enzymatic activities of liver microsomal NADH-cytochrome b 5 reductase in the latent and logarithmic phases of tumor growth as compared with non-irradiated tumor-bearing rats. At the same time the content of cytochrome b 5 decreased, while the rate of its oxidation-reduction rate simultaneously increased in the liver microsomal fraction of tumor-bearing rats. 相似文献
9.
Lederer F 《European biophysics journal : EBJ》2011,40(12):1283-1299
Yeast flavocytochrome b 2 tranfers reducing equivalents from lactate to oxygen via cytochrome c and cytochrome c oxidase. The enzyme catalytic cycle includes FMN reduction by lactate and reoxidation by intramolecular electron transfer to heme b 2. Each subunit of the soluble tetrameric enzyme consists of an N terminal b 5-like heme-binding domain and a C terminal flavodehydrogenase. In the crystal structure, FMN and heme are face to face, and appear to be in a suitable orientation and at a suitable distance for exchanging electrons. But in one subunit out of two, the heme domain is disordered and invisible. This raises a central question: is this mobility required for interaction with the physiological acceptor cytochrome c, which only receives electrons from the heme and not from the FMN? The present review summarizes the results of the variety of methods used over the years that shed light on the interactions between the flavin and heme domains and between the enzyme and cytochrome c. The conclusion is that one should consider the interaction between the flavin and heme domains as a transient one, and that the cytochrome c and the flavin domain docking areas on the heme b 2 domain must overlap at least in part. The heme domain mobility is an essential component of the flavocytochrome b 2 functioning. In this respect, the enzyme bears similarity to a variety of redox enzyme systems, in particular those in which a cytochrome b 5-like domain is fused to proteins carrying other redox functions. 相似文献
10.
Hirofumi Fukushima Shigenobu Umeki Takehito Watanabe Yoshinori Nozawa 《Biochemical and biophysical research communications》1982,105(2):502-508
With the use of detergents and successive column chromatographies, Tetrahymena b-type cytochrome was purified from microsomes to a specific content of 36.0 nmol per mg of protein. The purified form showed a single band on SDS-polyacrylamide gel with molecular weight of 22,000. The spectral properties of the reduced b-type cytochrome, the α-peak of which is situated at 560 nm and asymmetric with a shoulder at 556 nm, was different from that of rat liver microsomal cytochrome b5. However, it was reducible by NADH in the presence of NADH-cytochrome b5 reductase purified from rat liver microsomes.The results indicated that the microsomal b-type cytochrome should be designated as cytochrome b5 of a ciliated protozoan, Tetrahymena pyriformis. 相似文献
11.
(i) Compounds activating the microsomal electron transfer oxidative reactions, e.g., the mixed function oxidase (aminopyrine, aniline), the Δ9-desaturase (stearyl-CoA), and lipid peroxidation reaction (iron pyrophosphate), cause a decrease in the steady-state reduced level of cytochrome b5. (ii) In the absence of substrates, the kox for cytochrome b5 was the same whether reduced by NADH or NADPH (about 0.045 S?1, indicating that no distinction exists between the cytochrome b5 involved in NADH-driven and NADPH-driven microsomal reactions which utilize this hemoprotein. (iii) The agents activating the oxidative pathways affect the first-order rate constant for cytochrome b5 oxidation (kox), but the apparent first-order rate constant obtained for reduction (kred) of cytochrome b5 by NADPH is still more than 10 times the kox, and the kred obtained with NADH is still more than 100 times the kox. (iv) Of the compounds used, only stearyl-CoA caused a decrease in the NADH-supported steady-state reduced level of cytochrome b5. This effect is probably due to a detergent-like action of stearyl-CoA on the membrane proteins, interfering with some interactions (e.g., NADPH-cytochrome c reductase with cytochrome P-450; NADH-cytochrome b5 reductase with cytochrome b5). (v) Based upon the kinetic and steady-state measurements it is concluded that substrate-induced changes in the steady-state reduced level of cytochrome b5 are evidence for a decrease in the population of this hemoprotein available to the reductase due to competition with other more favored acceptors, (vi) Measurements using the duration of the reduced state and rates of electron flow through cytochrome b5 reveal that normally about 60% of the NADH-derived reducing equivalents go through cytochrome b5 while only about one electron in nine passes through this cytochrome when NADPH is the source of reducing equivalents. Substrates of the various pathways alter the proportion of electrons passing through cytochrome b5 depending upon their activating or inhibiting action on cytochrome b5-dependent or -independent reactions. 相似文献
12.
Electron transport from untreated to mersalyzed microsomal vesicles at the level of NADH-cytochrome b5 reductase or cytochrome b5 has been demonstrated in the absence of added water-soluble electron carriers. A similar effect was shown in the systems “intact mitochondria — mersalyzed microsomes” and “mersalyzed mitochondria— untreated microsomes”. No measurable electron transport between intact and mersalyzed particles of inner mitochondrial membrane was found. The obtained data suggest that the capability to carry out intermembrane electron transfer is specific for NADH-cytochrome b5 reductase and/or cytochrome b5, localized in microsomal and outer mitochondrial membranes. 相似文献
13.
Noor Khalidah Abdul Hamid Greta Carmona-Anto?anzas óscar Monroig Douglas R. Tocher Giovanni M. Turchini John A. Donald 《PloS one》2016,11(3)
Rainbow trout, Oncorhynchus mykiss, are intensively cultured globally. Understanding their requirement for long-chain polyunsaturated fatty acids (LC-PUFA) and the biochemistry of the enzymes and biosynthetic pathways required for fatty acid synthesis is important and highly relevant in current aquaculture. Most gnathostome vertebrates have two fatty acid desaturase (fads) genes with known functions in LC-PUFA biosynthesis and termed fads1 and fads2. However, teleost fish have exclusively fads2 genes. In rainbow trout, a fads2 cDNA had been previously cloned and found to encode an enzyme with Δ6 desaturase activity. In the present study, a second fads2 cDNA was cloned from the liver of rainbow trout and termed fads2b. The full-length mRNA contained 1578 nucleotides with an open reading frame of 1365 nucleotides that encoded a 454 amino acid protein with a predicted molecular weight of 52.48 kDa. The predicted Fads2b protein had the characteristic traits of the microsomal Fads family, including an N-terminal cytochrome b5 domain containing the heme-binding motif (HPPG), histidine boxes (HDXGH, HFQHH and QIEHH) and three transmembrane regions. The fads2b was expressed predominantly in the brain, liver, intestine and pyloric caeca. Expression of the fasd2b in yeast generated a protein that was found to specifically convert eicosatetraenoic acid (20:4n-3) to eicosapentaenoic acid (20:5n-3), and therefore functioned as a Δ5 desaturase. Therefore, rainbow trout have two fads2 genes that encode proteins with Δ5 and Δ6 desaturase activities, respectively, which enable this species to perform all the desaturation steps required for the biosynthesis of LC-PUFA from C18 precursors. 相似文献
14.
Gregory J. Workun Kamila Moquin Richard A. Rothery Joel H. Weiner 《Microbiology and molecular biology reviews》2008,72(2):228-248
Summary: The importance of molybdoenzymes is exemplified both by the debilitating and fatal human diseases caused by their deficiency and by their persistence throughout evolution. Here, we show that the protein fold of the molybdopyranopterin-containing domain of sulfite oxidase (the SUOX fold) can be found in all three domains of life. Analyses of sequence data and protein structure comparisons (secondary structure matching) show that the SUOX fold is found in enzymes that have quite distinct macromolecular architectures comprising one or more domains and sometimes subsidiary subunits. These are summarized as follows: (i) animal SUOXs that contain an N-terminal cytochrome b5 domain and an SUOX fold fused to a C-terminal dimerization domain; (ii) plant SUOX that contains an SUOX fold fused to a C-terminal dimerization domain; (iii) the YedY protein from Escherichia coli, which comprises only the SUOX fold; (iv) the sulfite dehydrogenase from Starkeya novella that contains the SUOX fold, a dimerization domain, and an additional c-type cytochrome subunit; and (v) the plant-type nitrate reductases, exemplified by that of Pichia angusta, that contain an N-terminal SUOX fold, a dimerization domain, a cytochrome b5 domain, and a C-terminal NADH binding flavin adenine dinucleotide-containing domain. We used the primary sequences of the proteins containing an SUOX fold to mine 559 sequences of related proteins. A phylogeny of a nonredundant subset of these sequences was generated, and the resultant clades were categorized by sequence motif analyses in the context of the available protein structures. Based on the motif analyses, cladistics, and domain conservations, we are able to postulate a plausible pathway of SUOX fold enzyme evolution. 相似文献
15.
An antibody preparation elicited against purified, lysosomal-solubilized NADH-cytochrome b5 reductase from rat liver microsomes was shown to interact with methemoglobin reductase of human erythrocytes by inhibiting the rate of erythrocyte cytochrome b5 reduction by NADH. The ferricyanide reductase activity of the enzyme was not inhibited by the antibody, suggesting that the inhibition of methemoglobin reductase activity may be due to interference with the binding of cytochrorme b5 to the flavoprotein. Under conditions of limiting concentrations of flavoprotein, the antibody inhibited the rate of methemoglobin reduction in a reconstituted system consisting of homogeneous methemoglobin reductase and cytochrome b5 from human erythrocytes. This inhibition was due to the decreased level of reduced cytochrome b5 during the steady state of methemoglobin reduction while the rate of methemoglobin reduction per reduced cytochrome b5 stayed constant, suggesting that the enzyme was not concerned with an electron transport between the reduced cytochrome b5 and methemoglobin.An antibody to purified, trypsin-solubilized cytochrome b5 from rat liver microsomes was shown to inhibit erythrocyte cytochrome b5 reduction by methemoglobin reductase and NADH to a lesser extent than microsomal cytochrome b5 preparations from rat liver (trypsin solubilized or detergent solubilized) and pig liver (trypsin solubilized). The results presented establish that soluble methemoglobin reductase and cytochrome b5 of human erythrocytes are immunochemically similar to NADH-cytochrome b5 reductase and cytochrome b5 of liver microsomes, respectively. 相似文献
16.
Purification and Characterization of Microsomal Cytochrome b(5) and NADH Cytochrome b(5) Reductase from Pisum sativum 总被引:2,自引:2,他引:0
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In this communication we document the reproducible protocols for the purification of milligram quantities of cytochrome b5 and NADH-cytochrome b5 reductase from the microsomal fraction of Pisum sativum. The cytochrome b5 component of this NADH linked electron transport chain was found to have a molecular mass of 16,400 daltons and the reductase a molecular mass of 34,500 daltons. These components could be reconstituted into a functional NADH oxidase activity active in the reduction of exogenous cytochrome c or ferricyanide. In the latter assay the purified reductase exhibited a turnover number of 22,000 per minute. The amino-terminal amino acid sequence of the cytochrome b5 component was determined by sequential Edmund degredation, thus providing crucial information for the efficient cloning of this central protein of plant microsomal electron transfer. 相似文献
17.
The role of NADH-cytochrome b5 reductase and cytochrome b5 as electron carriers in NADH-supported electron transport reactions in rat liver microsomes has been examined by measuring three enzyme activities: NADH-cytochrome P-450 reductase, NADH-peroxidase, and NADH-cytochrome c reductase. The first two reactions are known to involve the participation of an NADH-specific reductase and cytochrome P-450 whereas the third requires the reductase and cytochrome b5. Antibody prepared against NADH-cytochrome b5 reductase markedly inhibited the NADH-peroxidase and NADH-cytochrome c reductase activities suggesting the involvement of this NADH-specific reductase in these reactions. Liver microsomes prepared from phenobarbital-pretreated rats were digested with subtilisin to remove cytochrome b5 and the submicrosomal particles were collected by centrifugation. The specific content of cytochrome b5 in the digested particles was about 5% of that originally present in liver microsomes and all three enzyme activities showed similar decreases whereas NADH-ferricyanide reductase activity (an activity associated with the flavoenzyme NADH-cytochrome b5 reductase) remained virtually unchanged. Binding of an excess of detergent-purified cytochrome b5 to the submicrosomal particles at 37 °C for 20 min followed by centrifugation and enzymic measurements revealed a striking increase in the three enzyme activities. Further evidence for cytochrome b5 involvement in the NADH-peroxidase reaction was the marked inhibition by antibody prepared against the hemoprotein. These results suggest that in microsomal NADH-supported cytochrome P-450-dependent electron transport reactions, cytochrome b5 functions as an intermediate electron carrier between NADH-cytochrome b5 reductase and cytochrome P-450. 相似文献
18.
Homogeneous cytochrome b5 from human erythrocytes 总被引:3,自引:0,他引:3
D E Hultquist R T Dean R H Douglas 《Biochemical and biophysical research communications》1974,60(1):28-34
Homogeneous cytochrome b5 has been isolated from large volumes of human erythrocytes by sequential chromatography on DEAE-cellulose, Amberlite CG-50, Bio-Gel P-60, and DEAE-Sephadex A-50. A molecular weight of 15,300 was determined by SDS disc gel electrophoresis. Trypsin converted the protein to a smaller hemepeptide which was indistinguishable from trypsin-cytochrome b5 of human liver microsomes by disc gel electrophoresis. The data suggest that erythrocyte cytochrome b5 has the same structure as a segment of liver microsomal cytochrome b5 and is intermediate in size between the trypsin- and detergent-solubilized forms of the liver protein. 相似文献
19.
Peter Hlavica 《Archives of biochemistry and biophysics》1984,228(2):600-608
Complex formation between the phenobarbital-inducible form of rabbit liver microsomal cytochrome P-450 incorporated into phosphatidylcholine and detergent-solubilized cytochrome b5 is associated with a low-to-high spin transition of the former pigment. It is concluded that the proteins combine in a 1:1 molar ratio. CD spectral analysis in the far uv region reveals that interaction of the cytochromes results in a conformational change of one or both hemoproteins. Such a cytochrome b5-induced structural alteration of the reconstituted enzyme system is accompanied by an increase in affinity of 4-chloroaniline for cytochrome P-450, as measured in terms of cumene hydroperoxide-supported N-oxidation of the arylamine; the maximum velocity of the catalytic process remains unchanged. Similarly, incorporation into the assay media of cytochrome b5 decreases the apparent Kd values of both the amine substrate and the oxygen donor, as determined by optical titration. Stopped-flow spectrophotometric studies on the influence of cytochrome b5 on the kinetics of binding to cytochrome P-450 of 4-chloroaniline and/or cumene hydroperoxide show that the rates of formation and decay of the adducts change as the molar ratio of cytochrome b5 to cytochrome P-450 varies. Moreover, cytochrome b5 modifies the activation energies required for production of the substrate-bound oxy complex. These findings suggest that cytochrome b5, apart from its well-known role as an electron carrier, might exert an effector function in the cytochrome P-450 system. 相似文献
20.
The phenomenon of induction of the NADPH-specific hydroxylase system by sodium phenobarbital was used to determine the content of cytochrome b5 in each microsomal electron-transfer chain. It turned out that the specific activities of NADPH-dependent reductases and the cytochrome P-450 quantity were increased approximately 1.86 times and the activities of NADH-dependent reductases were somewhat decreased (0.89 times) in microsomes of induced rats. It is assumed that a subfraction of cytochrome b5 included in the NADPH-oxygenase complex is induced together with the other carriers of the chain. The second subfraction of the hemoprotein, in the course of induction, behaves as a typical component of the NADH-oxidizing complex. On the basis of the data obtained, the calculation was made, which showed that the NADPH-oxidation chain contains from to of the total microsomal cytochrome b5 pool. 相似文献