Overview of indigo biosynthesis by Flavin-containing Monooxygenases: History, industrialization challenges, and strategies

Indigo is a natural dye extensively used in the global textile industry. However, the conventional synthesis of indigo using toxic compounds like aniline, formaldehyde, and hydrogen cyanide has led to environmental pollution and health risks for workers. This method also faces growing economic, sustainability, and environmental challenges. To address these issues, the concept of bio-indigo or indigo biosynthesis has been proposed as an alternative to aniline-based indigo synthesis. Among various enzymes, Flavin-containing Monooxygenases (FMOs) have shown promise in achieving a high yield of bio-indigo. However, the industrialization of indigo biosynthesis still encounters several challenges. This review focuses on the historical development of indigo biosynthesis mediated by FMOs. It highlights several factors that have hindered industrialization, including the use of unsuitable chassis (Escherichia coli), the toxicity of indole, the high cost of the substrate L-tryptophan, the water-insolubility of the product indigo, the requirement of reducing reagents such as sodium dithionite, and the relatively low yield and high cost compared to chemical synthesis. Additionally, this paper summarizes various strategies to enhance the yield of indigo synthesized by FMOs, including redundant sequence deletion, semi-rational design, cheap precursor research, NADPH regeneration, large-scale fermentation, and enhancement of water solubility of indigo.

Enhanced production of bio-indigo in engineered Escherichia coli, reinforced by cyclopropane-fatty acid-acyl-phospholipid synthase from psychrophilic Pseudomonas sp. B14-6

Indigo dye is an organic compound with a distinctive blue color. Most of the indigo currently used in industry is produced via chemical synthesis, which generates a large amount of wastewater. Therefore, several studies have recently been conducted to find ways to produce indigo eco-friendly using microorganisms. Here, we produced indigo using recombinant Escherichia coli with both an indigo-producing plasmid and a cyclopropane fatty acid (CFA)-regulating plasmid. The CFA-regulating plasmid contains the cfa gene, and its expression increases the CFA composition of the phospholipid fatty acids of the cell membrane. Overexpression of cfa showed cytotoxicity resistance of indole, an intermediate product formed during the indigo production process. This had a positive effect on indigo production and cfa originated from Pseudomonas sp. B 14-6 was used. Optimal conditions for indigo production were determined by adjusting the expression strain, culture temperature, shaking speed, and isopropyl β-D-1-thiogalactopyranoside concentration. Treatment with Tween 80 at a particular concentration to increase the permeability of the cell membrane had a positive effect on indigo production. The strain with the CFA plasmid produced 4.1 mM of indigo after 24 h of culture and produced 1.5-fold higher indigo than the control strain without the CFA plasmid that produced 2.7 mM.

Structure-guided engineering of a flavin-containing monooxygenase for the efficient production of indirubin

Indirubin is a bisindole compound for the treatment of chronic myelocytic leukemia. Here, we presented a structure-guided method to improve the activity of a flavin-containing monooxygenase (bFMO) for the efficient production of indirubin in Escherichia coli. A flexible loop interlocked with the active pocket through a helix and the substrate tunnel rather than the active pocket in bFMO were identified to be two reconfigurable structures to improve its activity, resulting in K223R and N291T mutants with enhanced catalytic activity by 2.5- and 2.0-fold, respectively. A combined modification at the two regions (K223R/D317S) achieved a 6.6-fold improvement in catalytic efficiency (kcat/Km) due to enhancing π-π stacking interactions stabilization. Finally, an engineered E. coli strain was constructed by metabolic engineering, which could produce 860.7 mg/L (18 mg/L/h) indirubin, the highest yield ever reported. This work provides new insight into the redesign of FMOs to boost their activities and an efficient approach to produce indirubin.

Molecular and functional characterization of flavin-containing monooxygenases in pigs, dogs, and cats

Flavin-containing monooxygenases (FMOs) are drug-oxygenating enzymes that are present in the human genome as FMO1-5 and FMO6P. Among pig, dog, and cat FMOs, pig and dog FMO1 and FMO3 have been partly characterized, but other FMOs have not been systematically identified. In this study, orthologous FMO cDNAs were isolated from pig, dog, and cat livers and evaluated by sequence and phylogenetic analyses, tissue expression, and catalytic function. The amino acid sequences of pig, dog, and cat FMO1-5 shared high sequence identities (83-89%) with human FMO1-5 and were closely clustered in a phylogenetic tree. The gene structure and genomic organization of FMO1-5 were conserved across these species. Dog and pig FMO6P contained insertions of 1 and 83 bases, respectively, and are possibly pseudogenes similar to human FMO6P. Among the tissue types analyzed, pig FMO1 mRNA was abundant in liver, kidney, and lung; dog FMO3, FMO2, and FMO5 mRNAs were abundant in liver, lung, and kidney, respectively; cat FMO1 and FMO3 mRNAs were abundant in kidney and liver, respectively. Recombinant pig and dog FMO1-5 and cat FMO1-6 all mediated benzydamine and trimethylamine N-oxygenations and methyl p-tolyl sulfoxide S-oxygenation. The selective human FMO3 substrate trimethylamine was predominantly metabolized by pig FMO1, dog FMO3, and cat FMO3. Cat FMO6 was also active toward trimethylamine. These results suggest some similarities in the drug-metabolizing capabilities of FMO3 in dogs, cats, and humans and that dog and cat FMO3 generally have molecular and functional characteristics similar to human FMO3, being the major FMO in human liver.

Roles of selected non-P450 human oxidoreductase enzymes in protective and toxic effects of chemicals: review and compilation of reactions

This is an overview of the metabolic reactions of drugs, natural products, physiological compounds, and other (general) chemicals catalyzed by flavin monooxygenase (FMO), monoamine oxidase (MAO), NAD(P)H quinone oxidoreductase (NQO), and molybdenum hydroxylase enzymes (aldehyde oxidase (AOX) and xanthine oxidoreductase (XOR)), including roles as substrates, inducers, and inhibitors of the enzymes. The metabolism and bioactivation of selected examples of each group (i.e., drugs, “general chemicals,” natural products, and physiological compounds) are discussed. We identified a higher fraction of bioactivation reactions for FMO enzymes compared to other enzymes, predominately involving drugs and general chemicals. With MAO enzymes, physiological compounds predominate as substrates, and some products lead to unwanted side effects or illness. AOX and XOR enzymes are molybdenum hydroxylases that catalyze the oxidation of various heteroaromatic rings and aldehydes and the reduction of a number of different functional groups. While neither of these two enzymes contributes substantially to the metabolism of currently marketed drugs, AOX has become a frequently encountered route of metabolism among drug discovery programs in the past 10–15 years. XOR has even less of a role in the metabolism of clinical drugs and preclinical drug candidates than AOX, likely due to narrower substrate specificity.

Human flavin-containing monooxygenase 1 and its long-sought hydroperoxyflavin intermediate

Out of the five isoforms of human flavin-containing monooxygenase (hFMO), FMO1 and FMO3 are the most relevant to Phase I drug metabolism. They are involved in the oxygenation of xenobiotics including drugs and pesticides using NADPH and FAD as cofactors. Majority of the characterization of these enzymes has involved hFMO3, where intermediates of its catalytic cycle have been described. On the other hand, research efforts have so far failed in capturing the same key intermediate that is responsible for the monooxygenation activity of hFMO1. In this work we demonstrate spectrophotometrically the formation of a highly stable C4a-hydroperoxyflavin intermediate of hFMO1 upon reduction by NADPH and in the presence of O₂. The measured half-life of this flavin intermediate revealed it to be stable and not fully re-oxidized even after 30 min at 15 °C in the absence of substrate, the highest stability ever observed for a human FMO. In addition, the uncoupling reactions of hFMO1 show that this enzyme is <1% uncoupled in the presence of substrate, forming small amounts of H₂O₂ with no observable superoxide as confirmed by EPR spin trapping experiments. This behaviour is different from hFMO3, that is shown to form both H₂O₂ and superoxide anion radical as a result of ∼50% uncoupling. These data are consistent with the higher stability of the hFMO1 intermediate in comparison to hFMO3. Taken together, these data demonstrate the different behaviours of these two closely related enzymes with consequences for drug metabolism as well as possible toxicity due to reactive oxygen species.

Abscisic acid-mediated induction of FLAVIN-CONTAINING MONOOXYGENASE 2 leads to reduced accumulation of methylthioalkyl glucosinolates in Arabidopsis thaliana

Side-chain modification contributes to the structural diversity of aliphatic glucosinolates (GSLs), a class of sulfur-containing secondary metabolites found in Brassicales. The first step in side-chain modification of aliphatic GSLs is the S-oxygenation of the methylthioalkyl (MT) moiety to the methylsulfinylalkyl (MS) moiety. This reaction is catalyzed by flavin-containing monooxygenase (FMO_GS-OX), which is encoded by seven genes in Arabidopsis thaliana. Therefore, the regulation of FMO_GS-OX gene expression is key to controlling side-chain structural diversity. In this study, we demonstrated that the expression of FMO_GS-OX2 and FMO_GS-OX4 was induced by glucose treatment, independent of MYB28/29 and MYC2/3/4, the transcription factors that positively regulate aliphatic GSL biosynthesis. Glucose treatment of the abscisic acid (ABA)-related mutants indicated that glucose-triggered upregulation of FMO_GS-OX2 and FMO_GS-OX4 was partially regulated by ABA through the key negative regulators ABI1 and ABI2, and the positive regulator SnRK2, but not via the transcription factor ABI5. In wild-type plants, glucose treatment drastically reduced the accumulation of 4-methylthiobutyl (4MT) GSL, whereas a decrease in 4MT GSL was not observed in the fmo_gs-ox2, abi1-1, abi2-1, aba2-1, or aba3-1 mutants. This result indicated that the decreased accumulation of 4MT GSL by glucose treatment was attributed to upregulation of FMO_GS-OX2 via the ABA signaling pathway.

An indigo-producing plant, Polygonum tinctorium, possesses a flavin-containing monooxygenase capable of oxidizing indole

Polygonum tinctorium (P. tinctorium) is an indigo plant that is cultivated for a specific metabolite that it produces i.e., indoxyl β-D-glucoside (indican). In this study, flavin-containing monooxygenase (PtFMO) from P. tinctorium was cloned. When recombinant PtFMO was expressed in E. coli in the presence of tryptophan, indigo production was observed. Furthermore, we measured the activity of PtFMO using the membrane fraction from E. coli and found that it could produce indigo using indole as a substrate. The co-expression of PtFMO with indoxyl β-D-glucoside synthase (PtIGS), which catalyzes the glucosylation of indoxyl, brought about the formation of indican in E. coli. The results showed that indican was synthesized by sequential reactions of PtFMO and PtIGS. In three-week-old P. tinctorium specimens, the first leaves demonstrated higher levels of PtFMO expression than the subsequent leaves. This result coincided with that of our prior study on PtIGS expression level. Our study provides evidence that PtFMO might contribute to indican biosynthesis.

N- and S-oxygenation activity of truncated human flavin-containing monooxygenase 3 and its common polymorphic variants

Human flavin-containing monooxygenase 3 (FMO3) is a membrane-bound, phase I drug metabolizing enzyme. It is highly polymorphic with some of its variants demonstrating differences in rates of turnover of its substrates: xenobiotics including drugs as well as dietary compounds. In order to measure its in vitro activity and compare any differences between the wild type enzyme and its polymorphic variants, we undertook a systematic study using different engineered proteins, heterologously expressed in bacteria, purified and catalytically characterized with 3 different substrates. These included the full-length as well as the more soluble C-terminal truncated versions of the common polymorphic variants (E158K, V257M and E308G) of FMO3 in addition to the full-length and truncated wild-type proteins. In vitro activity assays were performed with benzydamine, tamoxifen and sulindac sulfide, whose products were measured by HPLC. Differences in catalytic properties between the wild-type FMO3 and its common polymorphic variants were similar to those observed with the truncated, more soluble versions of the enzymes. Interestingly, the truncated enzymes were better catalysts than the full-length proteins. The data obtained point to the feasibility of using the more soluble forms of this enzyme for in vitro drug assays as well as future biotechnological applications possibly in high throughput systems such as bioelectrochemical platforms and biosensors.

Production of indigo through the use of a dual-function substrate and a bifunctional fusion enzyme

The current chemical process for industrial indigo production puts a heavy burden on the environment. An attractive option would be to develop an alternative biotechnological process which does not rely on a petrochemical. This study describes a new biotransformation approach in which l-tryptophan is used as starting material. Its conversion to indigo can be achieved through recombinant overexpression of a bifunctional fusion enzyme, flavin-containing monooxygenase (FMO) fused to tryptophanase (TRP). First, TRP converts l-tryptophan into pyruvate, ammonia and indole. The formed indole serves as substrate for FMO, resulting in indigo formation, while pyruvate fuels the cells for regenerating the required NADPH. To optimize this bioconversion, different fusion constructs were tested. Fusing TRP to FMO at either the N-terminus (TRP-FMO) or the C-terminus (FMO-TRP) resulted in similar high expression levels of bifunctional fusion enzymes. Using whole cells and l-tryptophan as a precursor, high production levels of indigo could be obtained, significantly higher when compared with cells containing only overexpressed FMO. The TRP-FMO containing cells gave the highest yield of indigo resulting in full conversion of 2.0 g l-tryptophan into 1.7 g indigo per liter of culture. The process developed in this study provides an alternative biotransformation approach for the production of indigo starting from biobased starting material.

Uncoupled human flavin-containing monooxygenase 3 releases superoxide radical in addition to hydrogen peroxide

Human flavin-containing monooxygenase 3 (hFMO3) is a drug-metabolizing enzyme capable of performing N- or S-oxidation using the C4a-hydroperoxy intermediate. In this work, we employ both wild type hFMO3 as well as an active site polymorphic variant (N61S) to unravel the uncoupling reactions in the catalytic cycle of this enzyme. We demonstrate that in addition to H₂O₂ this enzyme also produces superoxide anion radicals as its uncoupling products. The level of uncoupling was found to vary between 50 and 70% (WT) and 90-98% (N61S) for incubations with NADPH and benzydamine over a period of 5 or 20 min, respectively. For the first time, we were able to follow the production of the superoxide radical in hFMO3, which was found to account for 13-18% of the total uncoupling of this human enzyme. Moreover, measurements in the presence or absence of the substrate show that the substrate lowers the level of uncoupling only related to the H₂O₂ and not the superoxide radical. This is consistent with the entry point of the substrate in this enzyme's catalytic cycle. These findings highlight the importance of the involvement of hFMO3 in the production of radicals in the endoplasmic reticulum, as well as the relevance of single-nucleotide polymorphism leading to deleterious effects of oxidative stress.

Hepatic Flavin-containing Monooxygenase and Aldehyde Oxidase Activities in Male Domestic Pigs at Different Ages

BACKGROUND

Age has a significant impact on activities of hepatic metabolizing enzymes in humans and animals. Flavin-containing Monooxygenase (FMO) and Aldehyde Oxidase (AO) are two important hepatic enzymes. Understanding of the impact of age on these two enzymes is still limited in pigs.

OBJECTIVE

The aim of this work was to assess hepatic FMO and AO activities of male domestic pigs at five different ages of 1 day, 2, 5, 10 and 20 weeks.

METHODS

Porcine liver microsomes and cytosol were prepared from the livers of male domestic pigs at ages of 1 day, 2, 5, 10 and 20 weeks. FMO activity was assessed using N-oxidation of benzydamine in porcine liver microsomes and AO activity was evaluated using oxidation of O6-benzylguanine in the porcine liver cytosol.

RESULTS

Porcine hepatic FMO activity was substantial at the age of 1 day, rapidly increased in 2 weeks, and remained high afterwards. Porcine hepatic AO activity was minimal at the age of 1 day and gradually increased to the maximum in 5 weeks and remained relatively constant to the age of 20 weeks. Porcine hepatic FMO activity is higher than other species, including humans. Age-dependent FMO developmental pattern in porcine liver is different from porcine hepatic CYP450 and human hepatic FMO. Porcine hepatic AO activity is much lower than humans although their developmental patterns are similar.

CONCLUSION

Age impact on hepatic activities of both FMO and AO is obvious in domestic male pigs although age patterns of both enzymes are different.

Thyrotoxic rubber antioxidants, 2-mercaptobenzimidazole and its methyl derivatives, cause both inhibition and induction of drug-metabolizing activity in rat liver microsomes after repeated oral administration

We examined the effects of thyrotoxic rubber antioxidants, 2-mercaptobenzimidazole (MBI, 0.3 mmol/kg/day) and its methyl derivatives, methyl-MBIs [4-methyl-MBI (4-MeMBI, 0.6 mmol/kg/day), 5-methyl-MBI (5-MeMBI, 0.6 mmol/kg/day), and 4(or 5)-methyl-MBI (4(5)-MeMBI, 0.6 or 1.2 mmol/kg/day)], on the drug-metabolizing activity in male rat liver microsomes by 8-day repeated oral administration. The weight of liver and thyroid were increased by all the test chemicals; MBI was most potent, and there was no additive or synergistic effect between 4-MeMBI and 5-MeMBI. MBI decreased the cytochrome P450 (CYP) content, NADPH-cytochrome P450 reductase (POR) activity, 7-ethoxycoumarin O-deethylation (ECOD) activity, and flavin-containing monooxygenase (FMO) activity, but increased the 7-pentoxyresorufin O-depentylation (PROD) activity, suggesting inhibition of the drug-metabolizing activity on the whole but induce some activities such as the CYP2B activity. On the contrary, all the methyl-MBIs increased the CYP content, CYB5 content, ECOD activity, 7-ethoxyresorufin O-deethylation (EROD) activity, and PROD activity, indicating that they are mostly inducible of the CYP activity. However, the methyl-MBIs decreased the FMO activity, and 5-MeMBI and 4(5)-MeMBI appeared inhibitory for CYPs 2C11 and 2C13. Between 4-MeMBI and 5-MeMBI, there was no additive or synergistic effect on the drug-metabolizing activity, but was counteraction. It was concluded that MBI and methyl-MBIs had both inhibitory and inducible effects on the drug-metabolizing activity in rat liver microsomes at thyrotoxic doses. The effects of 4(5)-MeMBI indicated that the increased liver weight alone can be a hepatotoxic sign but not an adaptive no-adverse response in toxicity studies. The present results were related to the toxicokinetic profiles of MBI and 4(5)-MeMBI in the repeated toxicity studies.

The metabolic fate of isotopically labeled trimethylamine-N-oxide (TMAO) in humans

Trimethylamine-N-oxide (TMAO) is associated with chronic disease risk. However, little is known about the metabolic fate of dietary TMAO. This study sought to quantitatively elucidate the metabolic fate of orally consumed TMAO in humans. As part of a crossover feeding study, healthy young men (n=40) consumed 50-mg deuterium-labeled methyl d9-TMAO (d9-TMAO), and enrichments of TMAO and its derivatives were measured in blood for 6 h, urine and stool, as well as skeletal muscle in a subset of men (n=6). Plasma d9-TMAO was detected as early as 15 min, increased until 1 h and remained elevated through the 6-h period. TMAO exhibited an estimated turnover time of 5.3 h, and ~96% of the dose was eliminated in urine by 24 h, mainly as d9-TMAO. No d9-TMAO was detected in feces. Notably, d9-TMAO and d9-trimethylamine were detected in skeletal muscle (n=6) at 6 h, and the enrichment ratio of d9-TMAO to d9-trimethylamine was influenced by a genetic variant in flavin-containing monooxygenase isoform 3 (FMO3 G472A). These results suggest that the absorption of orally consumed TMAO is near complete and does not require processing by gut microbes. TMAO exhibits fast turnover in the circulation with the majority being eliminated in urine within 24 h. A small portion of the dose, however, is taken up by extrahepatic tissue in a manner that appears to be under the influence of FMO3 G472A polymorphism. This trial was registered at clinicaltrials.gov as NCT02558673.

elegans flavin-containing monooxygenase-4 is essential for osmoregulation in hypotonic stress

Studies in Caenorhabditis elegans have revealed osmoregulatory systems engaged when worms experience hypertonic conditions, but less is known about measures employed when faced with hypotonic stress. Inactivation of fmo-4, which encodes flavin-containing monooxygenase-4, results in dramatic hypoosmotic hypersensitivity; worms are unable to prevent overwhelming water influx and swell rapidly, finally rupturing due to high internal hydrostatic pressure. fmo-4 is expressed prominently in hypodermis, duct and pore cells but is excluded from the excretory cell. Thus, FMO-4 plays a crucial osmoregulatory role by promoting clearance of excess water that enters during hypotonicity, perhaps by synthesizing an osmolyte that acts to establish an osmotic gradient from excretory cell to duct and pore cells. C. elegans FMO-4 contains a C-terminal extension conserved in all nematode FMO-4s. The coincidently numbered human FMO4 also contains an extended C-terminus with features similar to those of FMO-4. Although these shared sequence characteristics suggest potential orthology, human FMO4 was unable to rescue the fmo-4 osmoregulatory defect. Intriguingly, however, mammalian FMO4 is expressed predominantly in the kidney - an appropriate site if it too is, or once was, involved in osmoregulation.

Flavin-containing monooxygenase S-oxygenation of a series of thioureas and thiones

Mammalian flavin-containing monooxygenase (FMO) is active towards many drugs with a heteroatom having the properties of a soft nucleophile. Thiocarbamides and thiones are S-oxygenated to the sulfenic acid which can either react with glutathione and initiate a redox-cycle or be oxygenated a second time to the unstable sulfinic acid. In this study, we utilized LC-MS/MS to demonstrate that the oxygenation by hFMO of the thioureas under test terminated at the sulfenic acid. With thiones, hFMO catalyzed the second reaction and the sulfinic acid rapidly lost sulfite to form the corresponding imidazole. Thioureas are often pulmonary toxicants in mammals and, as previously reported by our laboratory, are excellent substrates for hFMO2. This isoform is expressed at high levels in the lung of most mammals, including non-human primates. Genotyping to date indicates that individuals of African (up to 49%) or Hispanic (2-7%) ancestry have at least one allele for functional hFMO2 in lung, but not Caucasians nor Asians. In this study the major metabolite formed by hFMO2 with thioureas from Allergan, Inc. was the sulfenic acid that reacted with glutathione. The majority of thiones were poor substrates for hFMO3, the major form in adult human liver. However, hFMO1, the major isoform expressed in infant and neonatal liver and adult kidney and intestine, readily S-oxygenated thiones under test, with Kms ranging from 7 to 160 μM and turnover numbers of 30-40 min(-1). The product formed was identified by LC-MS/MS as the imidazole. The activities of the mouse and human FMO1 and FMO3 orthologs were in good agreement with the exception of some thiones for which activity was much greater with hFMO1 than mFMO1.

Mammalian flavin-containing monooxygenase (FMO) as a source of hydrogen peroxide

Flavin-containing monooxygenase (FMO) oxygenates drugs/xenobiotics containing a soft nucleophile through a C4a hydroperoxy-FAD intermediate. Human FMOs 1, 2 and 3, expressed in Sf9 insect microsomes, released 30-50% of O₂ consumed as H₂O₂ upon addition of NADPH. Addition of substrate had little effect on H₂O₂ production. Two common FMO2 (the major isoform in the lung) genetic polymorphisms, S195L and N413K, were examined for generation of H₂O₂. FMO2 S195L exhibited higher "leakage", producing much greater amounts of H₂O₂, than ancestral FMO2 (FMO2.1) or the N413K variant. S195L was distinct in that H₂O₂ generation was much higher in the absence of substrate. Addition of superoxide dismutase did not impact H₂O₂ release. Catalase did not reduce levels of H₂O₂ with either FMO2.1 or FMO3 but inhibited H₂O₂ generated by FMO2 allelic variants N413K and S195L. These data are consistent with FMO molecular models. S195L resides in the GxGxSG/A NADP(+) binding motif, in which serine is highly conserved (76/89 known FMOs). We hypothesize that FMO, especially allelic variants such as FMO2 S195L, may enhance the toxicity of xenobiotics such as thioureas/thiocarbamides both by generation of sulfenic and sulfinic acid metabolites and enhanced release of reactive oxygen species (ROS) in the form of H₂O₂.

Flavin-containing monooxygenase, a new clue of pathological proteins in the rotenone model of parkinsonism

Parkinson's disease (PD) is a major age-related neurodegenerative disorder characterized by loss of dopaminergic neurons in the substantia nigra par compacta (SNpc) and accumulation of aggregated alpha-synuclein in brain areas. Rotenone is a neurotoxin that is routinely used to model PD, thus to help us understand the mechanisms of neural death. Flavin-containing monooxygenase (FMO), usually known as an important hepatic microsomal enzyme like cytochrome P450, was found to play a role in the brain recent years. In our study we aimed to find out the role that FMO might play in PD pathology. Thus we successfully generated rotenone model in primary midbrain dopaminergic neurons and identified the apoptosis of neurons caused by rotenone. We found that in rotenone model of Parkinsonism, the expression/protein level of parkin and FMO1 were decreased accompanied by the activation of caspase 3. Blocking FMO activity by FMO inhibitor methimazole directly caused activation of caspase 3, meanwhile parkin protein level was decreased. Our data indicated that FMO, whose dysfunction could be a reason for the apoptosis of dopaminergic neurons in rotenone model, might be a new clue of pathological proteins in rotenone model of parkinsonism. Meanwhile, it was suggested that parkin function was compromised in neuro-pathological states, thereby further adding to the cellular survival stress.

Determination of Cellular Localization of Expression of Flavin-Containing Monooxygenase Genes in Mouse Tissues by In Situ Hybridization

Methods are described for the cellular localization of expression of flavin-containing monooxygenase (FMO) genes in various mouse tissues by in situ hybridization. These include the production of digoxigenin (DIG)-labeled antisense and sense RNA probes by transcription from FMO cDNA templates, the preparation of paraffin wax-embedded and cryostat tissue sections, the hybridization of RNA probes to tissue sections, and the specific detection of hybridized probes using an antibody to DIG.

Expression of Recombinant Flavin-Containing Monooxygenases in a Baculovirus/Insect Cell System

The baculovirus/insect cell heterologous expression system provides an important tool for investigating the catalytic activity of individual drug-metabolizing enzymes toward a particular substrate. In this chapter we describe a baculovirus/insect cell system that we have used for the expression of human and mouse flavin-containing monooxygenases. Methods are described for the generation of recombinant baculoviral DNAs, via both site-specific transposition in Escherichia coli and site-specific recombination in vitro; adaptation of Spodoptera frugiperda (Sf) 9 cells to shaking culture and to serum-free medium; cryopreservation and transfection of Sf9 cells; amplification of baculovirus and determination of viral titer; analysis of baculoviral DNA; and expression and analysis of recombinant proteins.