Molecular Cloning, Escherichia coli Expression and Genomic Organization of Squalene Synthase Gene from Artemisia annua

A 1 539 by squalene synthase (AaSQS) cDNA was cloned from a high-yield Artemisia annua L. strain 001 by reverse transcription-polymerise chain reaction (RT-PCR). The amino acid sequence of AaSQS is 70%, 77%, 44% and 39%a identical to that of squalene synthases from Arabidopsis thaliana, tobacco, human and yeast, respectively. The AaSQS genomic DNA has a complex organization containing 14 exons and 13 introns. Full-length or C-terminal truncated cDNA was subcloned into prokaryotic expression vector pET30a and the constructed plasmid was introduced to Escherichia coli strain BL21 (DE3) for induced overexpression. No squalene synthase protein with expected molecular mass was observed in E. cola containing the putative full-length squalene synthase cDNA, however, overexpression in E. coli was achieved by truncating 30 amino acids of hydrophobic region at the carboxy terminus.

cDNA Cloning and Sequencing of Squalene Synthase of Artemisa apiacea

[Objective] cDNA from squalene synthase was cloned and sequenced.[Method] A pair of specific primers was designed according to the cDNA gene sequence of squalene synthase published in GenBank.Total RNA was extracted from the cell of Artemisia apiacea.The genes of squalene synthase were amplified by using RT-PCR.It was connected with pMD19-T vector and the cloned fragment sequences were analyzed.[Result] SS gene with the whole length of 1 257 bp was amplified and the fragment encoded 418 amino acids.The homo...

Detection and Analysis of Squalene in Oil from Olive Fruits of Different Varieties and of Different Degrees of Maturity

[Objective] This study aimed to identify the difference in squalene content among different olive varieties and the law of squalene content change in the same olive variety of different degrees of maturity, with the objective to provide technical support for the harvest and processing of olive fruits. [Method] Taking 13 introduced olive varieties including three varieties of eight different grades of maturity, fat acid w3s first extracted by Soxhlet extraction and then squalene was quantitatively and qualitatively analyzed by gas chromatography-mass spectrometry （GC-MS） method. [Result] The results showed that squalene content was the highest in CG-32, and the lowest in Leccino among the 13 olive varieties. And squalene content increased with the degree of maturity in the three olive varieties including CG-32, Frantoio and Ascolana Tenera. [Conclusion] A more simple and rapid method for the determina- tion of squatene content was established.

Dietary Effect of Squalene on Lipid Metabolism of Obese/Diabetes KK-<i>A^y</i>Mice and Wild-Type C57BL/6J Mice

The purpose of this study was to evaluate the influence of squalene (SQ) on plasma and hepatic lipid levels of obese/diabetic KK-Ay mice and wild-type C57BL/6J mice. SQ supplementation significantly increased the HDL cholesterol of KK-Ay mice, which was paralleled with no significant difference in the total and non-HDL cholesterol levels. The increase in HDL cholesterol was also found in the plasma of normal C57BL/6J mice, but the difference was not significant. SQ administration significantly increased neutral lipids (NL) in the liver of KK-Ay mice, while no significant difference was observed in the polar lipids and the total cholesterol levels. The increase in NL was primarily due to the increase in TAG. However, the cholesterol level significantly increased due to SQ intake in the liver of C57BL/6J mice, while no significant difference was found in other lipid levels. The present study suggests that SQ may effectively increase HDL cholesterol level, an important anti-atherosclerotic factor, especially in subjects with metabolic disorders.

Synthesis of Novel Hexathiolated Squalene and Its Thiol-Ene Photopolymerization with Unsaturated Monomers

In this work is described the synthesis of a multifunctional thiolated squalene. Thiol-ene coupling reactions were employed to functionalize the six double bonds of squalene, using thiolacetic acid. Hydrolysis of the resulting thioacetates, rendered the corresponding hexathiolated squalene SQ6SH. This compound was further photopolymerized separately with triallyl cyanurate, pentaerythritol triacrylate and diethyleneglycol divinyl ether. Real Time FTIR kinetics revealed that homopolymerization of the ene monomers took place in addition to the thiol-ene photopolymerization. Flexible films were obtained when SQ6SH was photopolymerized in bulk with the above mentioned unsaturated monomers.

Depletion of squalene epoxidase in synergy with glutathione peroxidase 4 inhibitor RSL3 overcomes oxidative stress resistance in lung squamous cell carcinoma

Background:Lung squamous cell carcinoma(Lusc)lacks effective targeted therapies and has a poor prognosis.Disruption of squalene epoxidase(SQLE)has been implicated in metabolic disorders and cancer.However,the role of SQLE as a monooxygenase involved in oxidativestressremainsunclear.Methods:We analyzed the expression and prognosis of lung adenocarcinoma(LUAD)and LUSC samples from GEO and TCGA databases.The proliferative activity of the tumors after intervention of SQLE was verified by cell and animal experiments.JC-1 assay,flow cytometry,and Western blot were used to show changes in apoptosis after intervention of sQLE.Flow cytometry and fluorescence assay of ROs levels were used to indicate oxidative stress status.Results:We investigated the unique role of SQLE expression in the diagnosis and prognosis prediction of LUSC.Knockdown of SQLE or treatment with the SQLE inhibitor terbinafine can suppress the proliferation of LUsC cells by inducing apoptosis and reactive oxygen species accumulation.However,depletion of SQLE also results in the impairment of lipid peroxidation and ferroptosis resistance such as upregulation of glutathione peroxidase 4.Therefore,prevention of SQLE in synergy with glutathione peroxidase 4 inhibitor RSL3 effectively mitigates the proliferation and growth of LUSC.Conclusion:Our study indicates that the low expression of sQLE employs adaptive survival through regulating the balance of apoptosis and ferroptosis resistance.In future,the combinational therapy of targeting sQLE and ferroptosis could be a promising approach in treating LUSC.

Plant-derived squalene supplementation improves growth performance and alleviates acute oxidative stress-induced growth retardation and intestinal damage in piglets

Piglets are particularly susceptible to oxidative stress,which causes inferior growth performance and intestinal damage.Squalene(SQ),a natural bioactive substance enriched in shark liver oil,shows excellent antioxidant properties and can currently be obtained at a low cost from deodorizer distillate during the production of plant oil.This study aimed to evaluate the effects of plant-derived SQ supplementation on the growth performance of piglets and explore the beneficial roles of SQ against oxidative stress and intestinal injury in diquat-challenged piglets.Forty piglets were randomly divided into five groups and fed a basal diet supplemented with SQ at 0,500,1000,or 2000 mg/kg for 5 weeks.Acute oxidative stress was induced in the piglets with diquat(10 mg/kg BW)at the fourth week of the experiment,followed by a 7-d recovery period.Results showed that before the diquat challenge,SQ supplementation significantly improved growth performance(average daily gain and feed conversion ratio)and serum antioxidant status,and after the diquat challenge,SQ supplementation significantly mitigated diquat-induced growth arrest,intestinal villous atrophy,intestinal epithelial cell apoptosis,intestinal hyperpermeability,and deficiency of intestinal epithelial tight junction proteins(zonula occludens-1,occludin,and claudin-3).Under oxidative stress induced by diquat,SQ supplementation consistently improved the antioxidant status of the small intestine,liver,and muscle.In vitro,SQ was shown to alleviate hydrogen peroxide(H2O2)-induced increase of the levels of intracellular reactive oxygen species and apoptosis of porcine intestinal epithelial cells.Taken together,SQ supplementation improves growth performance and effectively alleviates acute oxidative stress-induced growth retardation and intestinal injury via improving antioxidant capacity in piglets.Our findings may provide an efficient strategy for alleviating oxidative stress-induced inferior growth performance and intestinal damage in piglets.

Physical exercise reverses immuno-cold tumor microenvironment via inhibiting SQLE in non-small cell lung cancer

Dear Editor,Physical exercise has been shown to be associated with reduced cancer incidence and cancer-associated mortality[1,2],but the underlying mechanisms are obscure.Immunometabolic regulation has emerged as one of the most prominent mechanisms explaining the effects of exercise on cancer[1,2].Physical exercise primarily lowers blood cholesterol and triglycerides,and protects against cardiovascular diseases[3].However,whether physical exercise can modulate cholesterol metabolism in tumor cells is currently unknown.

Pumpkin seeds as nutraceutical and functional food ingredient for future:A review

Pumpkin belongs to the family of Cucurbitaceae,which comprises several species that has economical as well as agronomical importance.All parts of pumpkin are edible and laden with beneficial neutraceutical compounds.Pumpkin seeds are valuable source protein which can help in eradicating protein malnutrition and lipids(rich in PUFAs)contains essential as well as non essential fatty acids which prevents from various ailments like cancer and other cardiovascular diseases.Since,seeds of pumpkin are abundant in macro(magnesium,phosphorous,potassium,sodium and calcium)and micro minerals(iron,copper,manganese,zinc and selenium),they can be used as an incredible dietary supplement which in turn helps in curbing various deficiency disorders.This review enlightens the characteristics of pumpkin seeds,process of valorization of pumpkin seeds and the effect of processing on their nutritional composition which have been studied currently with the aim to use this wonder seeds for human wellbeing.Pumpkin seeds possess many bioactive compounds like polyphenols,flavonoids,phytosterols and squalene which makes it a lucrative raw material for pharmacological and food industries.Pumpkin seeds work as anti-depressant and helps majorly in the treatment of benign prostate hyperplasia(BHP).Daily consumption of pumpkin seeds can reduce the chances of Alzheimer's and Parkinson's disease.Pumpkin seeds are rich in tocopherols and can be used for oil extraction for edible purposes and utilized in other food formulations for future use.

Transcriptome-Wide Identification and Functional Analysis of PgSQE08-01 Gene in Ginsenoside Biosynthesis in Panax ginseng C.A.Mey.

Panax ginseng C.A.Mey.is an important plant species used in traditional Chinese medicine,whose primary active ingredient is a ginsenoside.Ginsenoside biosynthesis is not only regulated by transcription factors but also controlled by a variety of structural genes.Nonetheless,the molecular mechanism underlying ginsenoside biosynthesis has always been a topic in the discussion of ginseng secondary metabolites.Squalene epoxidase(SQE)is a key enzyme in the mevalonic acid pathway,which affects the biosynthesis of secondary metabolites such as terpenoid.Using ginseng transcriptome,expression,and ginsenoside content databases,this study employed bioinformatic methods to systematically analyze the genes encoding SQE in ginseng.We first selected six PgSQE candidates that were closely involved in ginsenoside biosynthesis and then identified PgSQE08-01 to be highly associated with ginsenoside biosynthesis.Next,we constructed the overexpression vector pCAMBIA3301-PgSQE08-01 and the RNAi vector pART27-PgSQE08-01 and transformed ginseng adventitious roots using Agrobacterium rhizogenes,to obtain positive hairy-root clones.Thereafter,quantitative reverse transcriptionpolymerase chain reaction and high-performance liquid chromatography were used to determine the expression of relevant genes and ginsenoside content,respectively.Then,we focused on the function of PgSQE08-01 gene,which was noted to be involved in ginsenoside biosynthesis.Thus,these findings not only provided a molecular basis for the identification of important functional genes in ginseng but also enriched genetic resources for the biosynthesis of ginsenosides using synthetic biology.

Cloning and characterization of squalene synthase and cycloartenol synthase from Siraitia grosvenorii

Mogrosides and steroid saponins are tetracyclic triterpenoids found in Siraitia grosvenorii.Squalene synthase(SQS) and cycloartenol synthase(CAS) are key enzymes in triterpenoid and steroid biosynthesis.In this study,full-length cDNAs of SgSQS and SgCAS were cloned by a rapid amplification of cDNA-ends with polymerase chain reaction(RACE-PCR) approach.The SgSQS cDNA has a 1254 bp open reading frame(ORF) encoding 417 amino acids,and the SgCAS cDNA contains a 2298 bp ORF encoding 765 amino acids.Bioinformatic analysis showed that the deduced SgSQS protein has two transmembrane regions in the C-terminal.Both SgSQS and SgCAS have significantly higher levels in fruits than in other tissues,suggesting that steroids and mogrosides are competitors for the same precursors in fruits.Combined in silico prediction and subcellular localization,experiments in tobacco indicated that SgSQS was probably in the cytoplasm or on the cytoskeleton,and SgCAS was likely located in the nucleus or cytosol.These results will provide a foundation for further study of SgSQS and SgCAS gene functions in S.grosvenorii,and may facilitate improvements in mogroside content in fruit by regulating gene expression.

Arabidopsis Squalene Epoxidase 3 （SQE3） Complements SQE1 and Is Important for Embryo Development and Bulk Squalene Epoxidase Activity

The existence of multigenic families in the mevalonate pathway suggests divergent functional roles for pathway components involved in the biosynthesis of plant sterols. Squalene epoxidases （SQEs） are key components of this pathway, and Squalene Epoxidase 1 （SQE1） has been identified as a fundamental enzyme in this biosynthetic step. In the present work, we extended the characterization of the remaining SQE family members, phylogenetically resolving between true SQEs and a subfamily of SQE-like proteins that is exclusive to Brassicaceae. Functional characterization of true SQE family members, Squalene Epox- idase 2 （SQE2） and Squalene Epoxidase 3 （SQE3）, indicates that SQE3, but not SQE2, contributes to the bulk SQE activity in Arabidopsis, with sqe3-1 mutants accumulating squalene and displaying sensitivity to ter- binafine. We genetically demonstrated that SQE3 seems to play a particularly significant role in embryo development. Also, SQE1 and SQE3 both localize in the endoplasmic reticulum, and SQE3 can functionally complement SQEI. Thus, SQE1 and SQE3 seem to be two functionally unequal redundant genes in the pro- motion of plant SQE activity in Arabidopsis.

Molecular Cloning and Expression of Squalene Epoxidase from a Medicinal Plant, Bupleurum chinense

Objective In plant, squalene epoxidase （SE） catalyzes the first oxygenation step in the biosynthetic pathway of triterpenoid and phytosterol, representing one of the rate-limiting enzymes in this pathway. Bupleurum chinense is an important medicinal herb with its major active constituents such as triterpenoid saponins and saikosaponins. In order to obtain the series of enzymatic genes involved in saikosaponin biosynthesis, a cDNA of SE, designated BcSEI, was cloned from B. chinense. Methods The BcSEI gene was cloned by homology-based PCR and 5＇/3＇ RACE methods from the adventitious roots of B. chinense. The physical and chemical parameters of BcSE1 protein were predicted by protparam. In order to discover hints in amino acid sequences on the dominant functions in the biosynthesis of saponin or phytosterol, sequences of SE from other plants were downloaded from NCBI for sequences alignment and phylogenetic analysis. BcSEI was cloned into a yeast mutant KLNI （MATa, ergl.＇：URA3, leu2, ura3, and trpl） to verify the enzyme activity of BcSE1. Additionally, the tissue-specific expression and methyl jasmonate （MeJA） inducibility of BcSEI were investigated using quantitative real-time PCR. Results The predicted protein of BcSE1 is highly similar to SEs from other plants sharing amino acid sequence identities of up to 88%. The BcSEI can functionally complement with yeast SE gene （ERGI） when expressed in the KLNI mutant （MATa, ergl：：URA3, leu2, ura3, and trpl）. Using as controls with ^-amyrin synthase （G-AS） which is presumed to catalyze the first committed step in saikosaponin biosynthesis and a cycloartenol synthase （CAS） relating to the phytosterol biosynthesis, the transcript of BcSE1 was significantly elevated by MeJA in adventitious roots of B. chinenseand the transcript of BcSElwas most abundant in the fruits and flowers of plants, followed by that in the leaves and roots, and least in stems. Conclusion It is the first time to illustrate the molecular information of SE in B. chinense and to clone the full-length SEgene in plants of genus Bupleurum L.

Squalene epoxidase promotes colorectal cancer cell proliferation through accumulating calcitriol and activating CYP24A1-mediatedMAPK signaling

Background:Colorectal cancer(CRC)is one of the most malignant tumorswith high incidence,yet its molecular mechanism is not fully understood,hindering the development of targeted therapy.Metabolic abnormalities are a hallmark of cancer.Targeting dysregulated metabolic features has become an important direction for modern anticancer therapy.In this study,we aimed to identify a new metabolic enzyme that promotes proliferation of CRC and to examine the related molecular mechanisms.Methods:We performed RNA sequencing and tissue microarray analyses of human CRC samples to identify new genes involved in CRC.Squalene epoxidase(SQLE)was identified to be highly upregulated in CRC patients.The regulatory function of SQLE in CRC progression and the therapeutic effect of SQLE inhibitors were determined by measuring CRC cell viability,colony and organoid formation,intracellular cholesterol concentration and xenograft tumor growth.Themolecularmechanism of SQLE functionwas explored by combining transcriptome and untargeted metabolomics analysis.Western blotting and realtime PCR were used to assess MAPK signaling activation by SQLE.Results:SQLE-related control of cholesterol biosynthesis was highly upregulated in CRC patients and associated with poor prognosis.SQLE promoted CRC growth in vitro and in vivo.Inhibition of SQLE reduced the levels of calcitriol(active form of vitamin D3)and CYP24A1,followed by an increase in intracellular Ca2+concentration.Subsequently,MAPK signaling was suppressed,resulting in the inhibition of CRC cell growth.Consistently,terbinafine,an SQLE inhibitor,suppressed CRC cell proliferation and organoid and xenograft tumor growth.Conclusions:Our findings demonstrate that SQLE promotes CRC through the accumulation of calcitriol and stimulation of CYP24A1-mediated MAPK signaling,highlighting SQLE as a potential therapeutic target for CRC treatment.

Mycorrhizas Affect Polyphyllin Accumulation of Paris polyphylla var.yunnanensis through Promoting PpSE Expression

Paris polyphylla var.yunnanensis is a traditional Chinese medicinal plant,in which polyphyllin as the main medicinal component is an important secondary metabolite with bioactivity.Arbuscular mycorrhizal fungi(AMF)have multiple positive effects on plants,while it is not clear whether AMF increase the content of medicinal components in medicinal plants.In this study,a total of nine AMF treatments were laid to analyze the mycorrhizal effect on polyphyllin accumulation and PpHMGR and PpSE expression of P.polyphylla var.yunnanensis.AMF increased the content of polyphyllin in the cultivated variety with low relation to the increase of inoculation intensity.Polyphyllin I,II,and VII were identified and partly improved by AMF inoculation,dependent on AMF treatments and culture environments.Similarly,the PpHMGR and PpSE expression was induced by mycorrhization,dependent on AMF species,whilst the induction was more obvious in PpSE than in PpHMGR after mycorrhization.It concluded that the symbiotic relationship between P.polyphylla var.yunnanensis and AMF increased polyphyllin content level in the plant,which was associated with the up-regulation of PpSE transcripts.

Effects of Arsenic Treatments on Saponin Content and Heterogeneity Extracted from Rhizome and Main Root of Panax notoginseng Plants Grown in Shaded Field

As contamination is one of important factors to Panax notoginseng quality and safety. Saponin is one of important compounds with the medicinal values of P. notoginseng. The impact of soil As on production of saponin of P. notoginseng knew very little. This study was performed to determine content and heterogeneity of saponins from P. notoginseng and its mechanisms upon treatments with different concentration levels of As in soil. Plants of P. notoginseng were treated with arsenic [As (V)] at 0, 20, 80, 140, 20 and 260 mg/kg concentration levels which were supplied as sodium arsenate (Na3AsO4). These experimental plants were grown in shade condition in a greenhouse. Plants were harvested at vigorous vegetative growth and fruit ripening stages, separately. Effects of As treatments on saponin content, and heterogeneity of monomers in the mixtures of notoginesenosides and ginsenosides, enzymatic activity and gene expression level of squalene synthetase were determined for rhizome and main root tissues. Results show that:(1) Of all the As treatments from the lowest to the highest concentration levels, the As content in both rhizome and main roots from As-treated plants was within the standard level for superior products derived from P. notoginseng. The content of notoginsenosides from all tissues except the main roots at fruit ripening stage, was 5% higher than the standard level specified in the Chinese Pharmacopoeia;(2) The treatment of As at 20 mg/kg led to an 3.5% - 183.9% increases in total notoginesenosides content in rhizome and main roots, respectively. Treatments with the highest As concentration at 260 mg/kg resulted in a significant decline in total notoginsenosides content, and lower enzymatic activity and gene expression levels of squalene synthetase;(3) Under As treatment conditions, the ratio of Rb1/Rg1 decreased but the ratio of (Rb1 + Rg1)/R1 increased in both rhizomes and main roots. Conclusively, this study demonstrated that low As concentration (20 - 80 mg/kg) treatments resulted in higher notoginsenoside content in P. notoginseng. However, treatments with high As concentrations had an adverse effect. The repression in the synthesis of notoginsenoside and interruption of the conversion process from propanaxadiol into propanaxatriol are responsible for more heterogeneous monomer mixtures and low notoginsenoside content. For plants treated with the highest As concentration of 260 mg/kg, both gene expression and enzymatic activities of squalene synthetase were greatly repressed thus leading to a significantly low saponin content in rhizome and main root tissues.

Functional characterization of triterpene synthases in Cibotium barometz

Cibotium barometz(Linn.)J.Sm.,a tree fern in the Dicksoniaceae family,is an economically important industrial exported plant in China and widely used in Traditional Chinese Medicine.C.barometz produces a range of bioactive triterpenes and their metabolites.However,the biosynthetic pathway of triterpenes in C.barometz remains unknown.To clarify the origin of diverse triterpenes in C.barometz,we conducted de novo transcriptome sequencing and analysis of C.barometz rhizomes and leaves to identify the candidate genes involved in C.barometz triterpene biosynthesis.Three C.barometz triterpene synthases(CbTSs)candidate genes were obtained.All of them were highly expressed in C.barometz rhizomes,consisting of the accumulation pattern of triterpenes in C.barometz.To characterize the function of these CbTSs,we constructed a squalene-and oxidosqualene-overproducing yeast chassis by overexpressing all the enzymes in the MVA pathway under the control of GAL-regulated promoter and disrupted the GAL80 gene in Saccharomyces cerevisiae simultaneously.Heterologous expressing CbTS1,CbTS2,and CbTS3 in engineering yeast strain produced cycloartenol,dammaradiene,and diploptene,respectively.Phylogenetic analysis revealed that CbTS1 belongs to oxidosqualene cyclase,while CbTS2 and CbTS3 belong to squalene cyclase.These results decipher enzymatic mechanisms underlying the origin of diverse triterpene in C.barometz.

Effect of light quality on total gypenosides accumulation and related key enzyme gene expression in Gynostemma pentaphyllum

Objective： Light quality has effect on the accumulation of gypenosides in the medicinal plant Gynosternma pentaphyllum in the family Cucurbitaceae, while the squalene synthase （SS） and squalene epoxidase （SE） are the key enzymes for gypenoside biosynthesis, The objective of this study was to elucidate the rela- tionship between light quality and biosynthesis key enzyme involving the regulation of gypenoside accu- mulation. Methods： The content of total gypenosides was measured by colorimetric method and the expression of SS and SE gene was determined by quantitative Real-time PCR in the seedlings of G. pentaphyllum which were grown with different light quality. Results： Light quality showed remarkable impacts on the accumulation of total gypenosides. The highest content of total gypenosides in the plant under red light condition was determined, followed by blue light and white light, while the lowest content was recorded under dark condition, qRT-PCR analysis proved that the expression levels of SS and SE genes were also affected by light quality. The high-level gene expressions of SS and SE were found in the plant under red light condition, followed by blue light, with the least content in darkness. The statistical analysis revealed that the total gypenosides were significantly different in different light treatment and the content of total gypenosides was positively related to the expression of SS and SE genes. Conclusions： Light quality regulates gypenoside accumulation via altering the expression of SS and SE in G. pentaphyllum.

Antifungal Activity of Aspidin BB from Dryopteris fragrans against Trichophyton rubrum Involved Inhibition of Ergosterol Biosynthesis

Objectives Aspidin BB, a typical phloroglucinol derivative from Dryopteris fragrans, possesses significant antifungal property. This study aimed to investigate potential mechanism of antifungal activity of Aspidin BB against Trichophyton rubrum which is the most common pathogens responsible for chronic dermatophytosis. Methods The minimum inhibitory concentration （MIC） ofAspidin BB against strains was determined by broth microdilution. The effects of Aspidin BB on ergosterol biosynthesis were investigated by content determination based on UPLC method. Besides, the effects of drugs on squalene epoxidase （SE） in T. rubrum cell membrane were analyzed. Results MIC value of Aspidin BB against T. rubrum was 25.0 IJg/mL. Aspidin BB reduced ergosterol content significantly, but no notable effect on squalene epoxidase activity. Conclusion The results suggested that Aspidin BB inhibited ergosterol biosynthesis. However, it was not squalene epoxidase but other components may sever as possible targets in ergosterol biosynthesis pathway.

New insights into the role of cytochrome P450 reductase (POR) in microsomal redox biology

Cytochrome P450 reductase(POR)is an essential electron transfer protein located on the endoplasmic reticulum of most cell types,and has long been appreciated for its role in cytochrome P450-mediated drug metabolism.Additional roles and electron acceptors for POR have been described,but it is largely with the recent availability of POR-null tissues that these supplemental roles for POR have been able to be explored.These studies have confirmed POR as the principal redox partner for the microsomal P450s responsible for drug and xenobiotic metabolism as well as cholesterol and bile acid synthesis,and for heme oxygenase,which catalyzes the initial step in the breakdown of heme.Surprisingly,these studies have revealed that squalene monooxygenase,an enzyme essential to cholesterol synthesis,has a second unknown redox partner in addition to POR,and that 7-dehydrocholesterol reductase,previously proposed to require POR as an electron donor,functions fully independently of POR.These studies have also helped define the role of cytochrome b5 in P450 catalysis,and raise the question as to the extent to which POR contributes to b5-dependent redox pathways.