Molecular cloning and tissue distribution of rat sarcosine dehydrogenase

Transcriptomics integrated with metabolomics reveals perfluorobutane sulfonate (PFBS) exposure effect during pregnancy and lactation on lipid metabolism in rat offspring

Emerging epidemiological evidence indicates potential associations between gestational perfluorobutane sulfonate (PFBS) exposure and adverse metabolic outcomes in offspring. However, the underlying mechanisms remain unclear. Our study aimed to investigate PFBS exposure effects during pregnancy and lactation on rat offspring lipid profiles and the possible underlying mechanisms. Although the biochemical index difference including total cholesterol (TC), triglyceride (TG), high-density lipoprotein (HDL), low-density lipoprotein (LDL), alanine amino transaminase (ALT), aspartate amino transferase (AST), and fasting blood glucose between exposed groups and the control group was not significant, transcriptome analyses showed that the differentially expressed genes (DEGs) in the 50 mg/kg/day PFBS exposure group were significantly related to protein digestion and absorption, peroxisome proliferator activated-receptor (PPAR) signaling pathway, xenobiotic metabolism by cytochrome P450, glycine, serine and threonine metabolism, β-alanine metabolism, bile secretion, unsaturated fatty acid (FA) biosynthesis, and alanine, aspartate and glutamate metabolism. Untargeted metabolomics analyses identified 17 differential metabolites in the 50 mg/kg/day PFBS exposure group. Among these, phosphatidylserine [PS (18:0/22:6(4Z,7Z,10Z,13Z,16Z,19Z))], lysoPE (18:1(11Z)/0:0), and PS (14:0/20:4(5Z,8Z,11Z,14Z)) were significantly correlated with phospholipid metabolism disorders. Correlation analysis indicated the DEGs, including FA binding protein (Fabp4), spermine oxidase (Smox), Fabp2, acyl-CoA thioesterase 5 (Acot5), sarcosine dehydrogenase (Sardh), and amine oxidase, copper-containing 3 (Aoc3) that significantly enriched in xenobiotic metabolism by cytochrome P450 and glycine, serine, and threonine metabolism signaling pathways were highly related to the differential metabolite pantetheine 4'-phosphate. Pantetheine 4'-phosphate was significantly negatively associated with non-high-density lipoprotein (non-HDL) and TC levels. Collectively, our study indicated that maternal PFBS exposure at a relatively low level could alter gene expression and metabolic molecules in lipid metabolism-related pathway series in rat offspring, although the effects on metabolic phenotypes were not significant within the limited observational period, using group-wise and trend analyses.

Transcriptome analysis of acute high temperature-responsive genes and pathways in Palaemon gravieri

Temperature is an important variable factor in aquaculture which affects the health, survival, behavior, growth, and development of aquatic animals. Palaemon gravieri is one of the main economic shrimps in marine capture fisheries of the East China Sea and the South China Yellow Sea; however, it cannot tolerate high temperatures, thereby, resulting in unsuccessful large-scale farming. Thus far, there are few studies on the effects of acute high temperature on P. graviera. Therefore, it is especially important to study the effects of temperature fluctuations, especially acute high temperature, on P. gravieri. In this study, P. gravieri was treated with acute high-temperature stress, which gradually rose from 15 °C to 30 °C in 3 h, then remained at 30 °C for 12 h. The hepatopancreas of shrimps from five time points was collected once at 15 °C and thereafter, every 3 h after 30 °C. The samples of G0, G1, and G4 were selected for transcriptome analysis. A total of 18,308 unigenes were annotated, of which 7744 were differentially expressed. Most differentially expressed genes (DEGs) come from several physiological and biochemical processes, such as metabolism (GRHPR, ALDH5A1, GDH), immunity (HSP70, Rab5B, Rab10, CASP7), and stress-related process (UGT, GST, HSP60, HSP90). The results indicated that acute high temperature significantly reduced the metabolic capacity of shrimp but enhanced the immune capacity, which seemed to be an emergency metabolic compensation technique to resist stress. This study contributes to ongoing research on the physiological mechanism of P. gravieri response to acute high temperature.

Metabolomic-based clinical studies and murine models for acute pancreatitis disease: A review

Acute pancreatitis (AP) is one of the most common gastroenterological disorders requiring hospitalization and is associated with substantial morbidity and mortality. Metabolomics nowadays not only help us to understand cellular metabolism to a degree that was not previously obtainable, but also to reveal the importance of the metabolites in physiological control, disease onset and development. An in-depth understanding of metabolic phenotyping would be therefore crucial for accurate diagnosis, prognosis and precise treatment of AP. In this review, we summarized and addressed the metabolomics design and workflow in AP studies, as well as the results and analysis of the in-depth of research. Based on the metabolic profiling work in both clinical populations and experimental AP models, we described the metabolites with potential utility as biomarkers and the correlation between the altered metabolites and AP status. Moreover, the disturbed metabolic pathways correlated with biological function were discussed in the end. A practical understanding of current and emerging metabolomic approaches applicable to AP and use of the metabolite information presented will aid in designing robust metabolomics and biological experiments that result in identification of unique biomarkers and mechanisms, and ultimately enhanced clinical decision-making.

Molecular cloning of rat acss3 and characterization of mammalian propionyl-CoA synthetase in the liver mitochondrial matrix

Among the three acyl-CoA synthetase short-chain family members (ACSS), ACSS3 is poorly characterized. To characterize ACSS3, we performed molecular cloning and protein expression of rat acss3 and determined its intracellular localization, tissue distribution, and substrate specificity. Transient expression of rat ACSS3 in HeLa cells resulted in a 10-fold increase of acetyl-CoA synthetase activity compared with that in control cells. The acss3 transcripts are expressed in a wide range of tissues, with the highest levels observed in liver tissue followed by kidney tissue. Subcellular fractionation using liver tissue showed that ACSS3 is localized into the mitochondrial matrix. Among the short-chain fatty acids examined, recombinant ACSS3, purified from Escherichia coli cells transformed with the plasmid containing rat acss3, preferentially utilized propionate with a KM value of 0.19 mM. Knockdown of acss3 in HepG2 cells resulted in a significant decrease of ACSS3 expression level and propionyl-CoA synthetase activity in cell lysates. Levels of ACSS3 in the liver and the activity of propionyl-CoA synthetase in the mitochondria were significantly increased by fasting. These results suggested that ACSS3 is a liver mitochondrial matrix enzyme with high affinity to propionic acid, and its expression level is upregulated under ketogenic conditions.

Preclinical Evaluation of 11C-Sarcosine as a Substrate of Proton-Coupled Amino Acid Transporters and First Human Application in Prostate Cancer

Sarcosine is a known substrate of proton-coupled amino acid transporters (PATs), which are overexpressed in selected tissues and solid tumors. Sarcosine, an N-methyl derivative of the amino acid glycine and a metabolic product of choline, plays an important role for prostate cancer aggressiveness and progression. Methods:¹¹C-radiolabeled sarcosine was tested as a new PET imaging probe in comparison with ¹¹C-choline in 2 prostate cancer tumor xenograft models (DU-145 and PC-3). We characterized ¹¹C-sarcosine transport in PC-3 and LNCaP tumor cells and performed ¹¹C-sarcosine PET with CT in the first human subject with localized Gleason 4 + 3 prostate cancer. Target metabolite analyses of sarcosine and its natural precursors, glycine and choline, were performed from independent human prostate tissues. Results: In vitro assays indicated blockage of ¹¹C-sarcosine uptake into PC-3 and LNCaP tumor cells by excess unlabeled (cold) sarcosine. 5-hydroxy-l-tryptophan, but not 2-aminobicyclo-(2,2,1)-heptane-2-carboxylic acid, competitively inhibited ¹¹C-sarcosine tumor cell uptake, confirming PAT-mediated transport. In vivo tumor-to-background ratios (TBRs) obtained from ¹¹C-sarcosine PET were significantly elevated compared with ¹¹C-choline in DU-145 (TBR: 1.92 ± 0.11 for ¹¹C-sarcosine vs. 1.41 ± 0.13 for ¹¹C-choline [n = 10; P < 0.002]) and PC-3 tumors (TBR: 1.89 ± 0.2 for ¹¹C-sarcosine vs. 1.34 ± 0.16 for ¹¹C-choline [n = 7; P < 0.002]). ¹¹C-sarcosine produced high-contrast images in 1 case of localized clinically significant prostate cancer. Target metabolite analyses revealed significant stepwise increases of sarcosine, glycine, and choline tissue levels from benign prostate tissue to localized prostate cancer and subsequently metastatic disease. ¹¹C-sarcosine showed a favorable radiation dosimetry with an effective dose estimate of 0.0045 mSv/MBq, resulting in 2.68 mSv for a human subject (600-MBq dose). Conclusion:¹¹C-sarcosine is a novel radiotracer for PATs and shows initial utility for prostate cancer imaging, with potential benefit over commonly used ¹¹C-choline.

Evaluation of Oxidative Stress Parameters and Energy Metabolism in Cerebral Cortex of Rats Subjected to Sarcosine Administration

Sarcosine is an N-methyl derivative of the amino acid glycine, and its elevation in tissues and physiological fluids of patients with sarcosinemia could reflect a deficient pool size of activated 1-carbon units. Sarcosinemia is a rare inherited metabolic condition associated with mental retardation. In the present study, we investigated the acute effect of sarcosine and/or creatine plus pyruvate on some parameters of oxidative stress and energy metabolism in cerebral cortex homogenates of 21-day-old Wistar rats. Acute administration of sarcosine induced oxidative stress and diminished the activities of adenylate kinase, GAPDH, complex IV, and mitochondrial and cytosolic creatine kinase. On the other hand, succinate dehydrogenase activity was enhanced in cerebral cortex of rats. Moreover, total sulfhydryl content was significantly diminished, while DCFH oxidation, TBARS content, and activities of SOD and GPx were significantly enhanced by acute administration of sarcosine. Co-administration of creatine plus pyruvate was effective in the prevention of alterations provoked by sarcosine administration on the oxidative stress and the enzymes of phosphoryltransfer network. These results indicate that acute administration of sarcosine may stimulate oxidative stress and alter the energy metabolism in cerebral cortex of rats. In case these effects also occur in humans, they may contribute, along with other mechanisms, to the neurological dysfunction of sarcosinemia, and creatine and pyruvate supplementation could be beneficial to the patients.

Chemically induced acute model of sarcosinemia in wistar rats

In the present study, we developed an acute chemically induced model of sarcosinemia in Wistar rats. Wistar rats of 7, 14 and 21 postpartum days received sarcosine intraperitoneally in doses of 0.5 mmol/Kg of body weight three time a day at intervals of 3 h. Control animals received saline solution (NaCl 0.85 g%) in the same volume (10 mL/Kg of body weight). The animals were killed after 30 min, 1, 2, 3 or 6 h after the last injection and the brain and the blood were collected for sarcosine measurement. The results showed that plasma and brain sarcosine concentrations achieved levels three to four times higher than the normal levels and decreased in a time-dependent way, achieving normal levels after 6 hours. Considering that experimental animal models are useful to investigate the pathophysiology of human disorders, our model of sarcosinemia may be useful for the research of the mechanisms of neurological dysfunction caused by high tissue sarcosine levels.

Sarcosine as a potential prostate cancer biomarker--a review

Prostate cancer (CaP) is the most common type of tumour disease in men. Early diagnosis of cancer of the prostate is very important, because the sooner the cancer is detected, the better it is treated. According to that fact, there is great interest in the finding of new markers including amino acids, proteins or nucleic acids. Prostate specific antigen (PSA) is commonly used and is the most important biomarker of CaP. This marker can only be detected in blood and its sensitivity is approximately 80%. Moreover, early stages cannot be diagnosed using this protein. Currently, there does not exist a test for diagnosis of early stages of prostate cancer. This fact motivates us to find markers sensitive to the early stages of CaP, which are easily detected in body fluids including urine. A potential is therefore attributed to the non-protein amino acid sarcosine, which is generated by glycine-N-methyltransferase in its biochemical cycle. In this review, we summarize analytical methods for quantification of sarcosine as a CaP marker. Moreover, pathways of the connection of synthesis of sarcosine and CaP development are discussed.

Glycine metabolism in animals and humans: implications for nutrition and health

Glycine is a major amino acid in mammals and other animals. It is synthesized from serine, threonine, choline, and hydroxyproline via inter-organ metabolism involving primarily the liver and kidneys. Under normal feeding conditions, glycine is not adequately synthesized in birds or in other animals, particularly in a diseased state. Glycine degradation occurs through three pathways: the glycine cleavage system (GCS), serine hydroxymethyltransferase, and conversion to glyoxylate by peroxisomal D-amino acid oxidase. Among these pathways, GCS is the major enzyme to initiate glycine degradation to form ammonia and CO2 in animals. In addition, glycine is utilized for the biosynthesis of glutathione, heme, creatine, nucleic acids, and uric acid. Furthermore, glycine is a significant component of bile acids secreted into the lumen of the small intestine that is necessary for the digestion of dietary fat and the absorption of long-chain fatty acids. Glycine plays an important role in metabolic regulation, anti-oxidative reactions, and neurological function. Thus, this nutrient has been used to: (1) prevent tissue injury; (2) enhance anti-oxidative capacity; (3) promote protein synthesis and wound healing; (4) improve immunity; and (5) treat metabolic disorders in obesity, diabetes, cardiovascular disease, ischemia-reperfusion injuries, cancers, and various inflammatory diseases. These multiple beneficial effects of glycine, coupled with its insufficient de novo synthesis, support the notion that it is a conditionally essential and also a functional amino acid for mammals (including pigs and humans).

Characterization of the neuropsychological phenotype of glycine N-methyltransferase-/- mice and evaluation of its responses to clozapine and sarcosine treatments

Glycine N-methyltransferase (GNMT) affects cellular methylation capacity through regulating the ratio between S-adenosylmethionine (SAM) and S-adenosylhomocysteine (SAH). The product of its enzymatic reaction-sarcosine has antipsychotic effect in patients with schizophrenia. In this study, through RT-PCR and immunohistochemical staining, we demonstrated that GNMT expressed in various neurons located in the cerebral cortex, hippocampus, substantia nigra and cerebellum. Compared to the wild-type mice, Gnmt-/- mice had significantly lower level of sarcosine in the cerebral cortex. Real-time PCR identified genes involved in the methionine metabolism (Dnmt1 and Dnmt3a), ErbB (Nrg1 and ErbB4) and mTOR (Akt2, S6, S6k1 and S6k2) signaling pathways were dysregulated significantly in the cortex of Gnmt-/- mice. Acoustic startle reflex test demonstrated that Gnmt-/- mice had significantly lower level of prepulse inhibition and the deficit was ameliorated through clozapine or sarcosine treatment. Furthermore, liver-specific-human-GNMT transgenic with Gnmt-/- (Tg-GNMT/Gnmt-/-) mice were used to rule out that the phenotype was due to abnormal liver function. In summary, the neuropsychological abnormalities found in Gnmt-/- mice may represent an endophenotype of schizophrenia. GNMT plays an important role in maintaining normal physiological function of brain and Tg-GNMT/Gnmt-/- mice are useful models for development of therapeutics for patients with schizophrenia.

The tumor suppressor activity of the transmembrane protein with epidermal growth factor and two follistatin motifs 2 (TMEFF2) correlates with its ability to modulate sarcosine levels

The type I transmembrane protein with epidermal growth factor and two follistatin motifs 2 (TMEFF2) is expressed in brain and prostate and overexpressed in prostate cancer, but its role in this disease is unclear. Several studies have suggested that TMEFF2 plays a role in suppressing the growth and invasive potential of human cancer cells, whereas others suggest that the shed portion of TMEFF2, which lacks the cytoplasmic region, has a growth-promoting activity. Here we show that TMEFF2 has a dual mode of action. Ectopic expression of wild-type full-length TMEFF2 inhibits soft agar colony formation, cellular invasion, and migration and increases cellular sensitivity to apoptosis. However, expression of the ectodomain portion of TMEFF2 increases cell proliferation. Using affinity chromatography and mass spectrometry, we identify sarcosine dehydrogenase (SARDH), the enzyme that converts sarcosine to glycine, as a TMEFF2-interacting protein. Co-immunoprecipitation and immunofluorescence analysis confirms the interaction of SARDH with full-length TMEFF2. The ectodomain does not bind to SARDH. Moreover, expression of the full-length TMEFF2 but not the ectodomain results in a decreased level of sarcosine in the cells. These results suggest that the tumor suppressor activity of TMEFF2 requires the cytoplasmic/transmembrane portion of the protein and correlates with its ability to bind to SARDH and to modulate the level of sarcosine.

Mammalian MTHFD2L encodes a mitochondrial methylenetetrahydrofolate dehydrogenase isozyme expressed in adult tissues

Previous studies in our laboratory showed that isolated, intact adult rat liver mitochondria are able to oxidize the 3-carbon of serine and the N-methyl carbon of sarcosine to formate without the addition of any other cofactors or substrates. Conversion of these 1-carbon units to formate requires several folate-interconverting enzymes in mitochondria. The enzyme(s) responsible for conversion of 5,10-methylene-tetrahydrofolate (CH(2)-THF) to 10-formyl-THF in adult mammalian mitochondria are currently unknown. A new mitochondrial CH(2)-THF dehydrogenase isozyme, encoded by the MTHFD2L gene, has now been identified. The recombinant protein exhibits robust NADP(+)-dependent CH(2)-THF dehydrogenase activity when expressed in yeast. The enzyme is localized to mitochondria when expressed in CHO cells and behaves as a peripheral membrane protein, tightly associated with the matrix side of the mitochondrial inner membrane. The MTHFD2L gene is subject to alternative splicing and is expressed in adult tissues in humans and rodents. This CH(2)-THF dehydrogenase isozyme thus fills the remaining gap in the pathway from CH(2)-THF to formate in adult mammalian mitochondria.

Compartmentalization of Mammalian folate-mediated one-carbon metabolism

The recognition that mitochondria participate in folate-mediated one-carbon metabolism grew out of pioneering work beginning in the 1950s from the laboratories of D.M. Greenberg, C.G. Mackenzie, and G. Kikuchi. These studies revealed mitochondria as the site of oxidation of one-carbon donors such as serine, glycine, sarcosine, and dimethylglycine. Subsequent work from these laboratories and others demonstrated the participation of folate coenzymes and folate-dependent enzymes in these mitochondrial processes. Biochemical and molecular genetic approaches in the 1980s and 1990s identified many of the enzymes involved and revealed an interdependence of cytoplasmic and mitochondrial one-carbon metabolism. These studies led to the development of a model of eukaryotic one-carbon metabolism that comprises parallel cytosolic and mitochondrial pathways, connected by one-carbon donors such as serine, glycine, and formate. Sequencing of the human and other mammalian genomes has facilitated identification of the enzymes that participate in this intercompartmental one-carbon metabolism, and animal models are beginning to clarify the roles of the cytoplasmic and mitochondrial isozymes of these enzymes. Identifying the mitochondrial transporters for the one-carbon donors and elucidating how flux through these pathways is controlled are two areas ripe for exploration.

The glycine transport inhibitor sarcosine is an inhibitory glycine receptor agonist

Sarcosine is an endogenous amino acid that is a competitive inhibitor of the type I glycine transporter (GlyT1), an N-methyl-d-aspartate receptor (NMDAR) co-agonist, and an important intermediate in one-carbon metabolism. Its therapeutic potential for schizophrenia further underscores its clinical importance. The structural similarity between sarcosine and glycine and sarcosine's ability to serve as an NMDAR co-agonist led us to examine whether sarcosine is also an agonist at the inhibitory glycine receptor (GlyR). We examined this possibility using whole-cell recordings from cultured embryonic mouse hippocampal neurons and found that sarcosine evoked a dose-dependent, strychnine sensitive, Cl(-) current that cross-inhibited glycine currents. Sarcosine evoked this current with Li(+) in the extracellular solution to block GlyT1, in neurons treated with the essentially irreversible GlyT1 inhibitor N[3-(4'-fluorophenyl)-3-(4'-phenylphenoxy)propyl]sarcosine (NFPS), and in neurons plated in the absence of glia. These results indicate that the sarcosine currents did not result from GlyT1 inhibition or heteroexchange. We conclude that sarcosine is a GlyR agonist.

Prefrontal cortex and spinal cord mediated anti-neuropathy and analgesia induced by sarcosine, a glycine-T1 transporter inhibitor

Sarcosine is a competitive inhibitor of glycine type 1 transporter. We hypothesized that it may have analgesic and anti-neuropathic efficacy by a dual action: affecting neurotransmission in the prefrontal cortex as well as within the spinal cord. In rats with spared nerve injury (SNI) oral sarcosine reduced mechanical sensitivity for the injured limb (anti-neuropathy or anti-allodynia) as well as for the uninjured limb (analgesia), showing better dose efficacy for the injured limb. Intrathecal administration of sarcosine was more effective in reducing mechanical sensitivity for the uninjured paw. In contrast, prefrontal cortex infusions of sarcosine acutely reduced mechanical sensitivity for the injured paw. Repeated daily oral sarcosine induced anti-neuropathy, observed only after days of repeated treatment; this long-term effect disappeared a few days after treatment cessation. The findings indicate that manipulating glycine-T1 transporter at multiple central sites can induce acute analgesia, as well as acute and long-term reduction in neuropathic pain behavior. Analgesic effects seem primarily mediated through spinal cord circuitry while anti-neuropathic effects seem mediated through prefrontal cortex circuitry, most likely through distinct molecular pathways. The results suggest that such an approach may provide a novel venue for treating clinical pain conditions.

Transcriptome profiling analysis reveals multiple modulatory effects of Ginkgo biloba extract in the liver of rats on a high-fat diet

Leaf extract of Ginkgo biloba (GBE) is increasingly used as a herbal medicine for the treatment of neurodegenerative, cardiovascular and cerebrovascular diseases. Several studies have demonstrated many protective effects of GBE in neurons, the endothelium and liver. In this study, we investigated the molecular mechanisms underlying the effects of GBE in disorders induced by long-term exposure to a high-fat diet (HFD). Rats were fed an HFD with or without the GBE product GBE50 for 19 weeks. We found that GBE50 reduced the development of fatty liver induced by an HFD and inhibited the commonly observed elevation of serum cholesterol and lactate dehydrogenase levels. Transcriptome profiling analysis showed that several genes were modulated by GBE50 in liver, including those involved in lipid metabolism, carbohydrate metabolism, vascular constriction, ion transportation, neuronal systems and drug metabolism. Notably, a number of genes coding for proteins involved in cholesterol metabolism were repressed, and some were upregulated. Fatty acid biosynthesis appeared to be repressed, whereas fatty acid metabolism appeared to be enhanced. In conclusion, using transcriptome profiling analysis, we demonstrated the molecular basis for the pleiotropic effects of GBE50, particularly those involved in lipid metabolism. This study provided new clues for further pharmacological study of GBEs.

Human mitochondrial C1-tetrahydrofolate synthase: submitochondrial localization of the full-length enzyme and characterization of a short isoform

Mammalian mitochondrial C(1)-tetrahydrofolate (THF) synthase (MTHFDIL gene product) is a monofunctional 10-formyl-THF synthetase, lacking the 5,10-methylene-THF dehydrogenase and 5,10-methenyl-THF cyclohydrolase activities typically found in the trifunctional cytoplasmic proteins. Here, we report the submitochondrial localization of epitope-tagged human mitochondrial C(1)-THF synthase expressed in Chinese hamster ovary cells. Mitochondrial fractionation experiments show that human mitochondrial C(1)-THF synthase behaves as a peripheral membrane protein, tightly associated with the matrix side of the mitochondrial inner membrane. Inner mitochondrial membrane association was also observed for the endogenous mitochondrial C(1)-THF synthase in adult rat spleen. We also purified and characterized the recombinant protein product (short isoform) of the alternatively spliced short transcript of the mitochondrial isozyme. Methylene-THF dehydrogenase assays confirmed that the short isoform is not enzymatically active. The purified short isoform was used in the production of polyclonal antibodies specific for the mitochondrial isozyme. These antibodies detected endogenous full-length mitochondrial C(1)-THF synthase in mitochondria from adult rat spleen and human placenta, confirming the expression of the mitochondrial isozyme in adult mammalian tissues.

A targeted proteomic approach for the analysis of rat liver mitochondrial outer membrane proteins with extensive sequence coverage

Membrane proteins play an important role in cellular function. However, their analysis by mass spectrometry often is hindered by their hydrophobicity and/or low abundance. In this article, we present a method for the mass spectrometric analysis of membrane proteins based on the isolation of the resident membranes, isolation of the proteins by gel electrophoresis, and electroelution followed by enzymatic digestion by both trypsin and proteinase K. With this method, we have achieved 82-99% sequence coverage for the membrane proteins carnitine palmitoyltransferase-I (CPT-I), long-chain acyl-CoA synthetase (LCAS), and voltage-dependent anion channel (VDAC), isolated from rat liver mitochondrial outer membranes, including the transmembrane domains of these integral membrane proteins. This high sequence coverage allowed the identification of the isoforms of the proteins under study. This methodology provides a targeted approach for examining membrane proteins in detail.

Microbiology and biochemistry of nicotine degradation

Several bacterial species are adapted to nicotine, the main alkaloid produced by the tobacco plant, as growth substrate. A general outline of nicotine catabolism by these bacteria is presented, followed by an emphasis on new insights based on molecular biology and biochemical work obtained with the catabolic plasmid pAO1 of Arthrobacter nicotinovorans. Its 165-kb sequence revealed the genetic structure of nicotine catabolism and allowed the assignment of new enzyme activities to specific gene products, which extends the known biochemical steps of this pathway. Potential implications of the progress in our understanding of bacterial breakdown of nicotine for biotechnological applications are discussed.

A novel gamma-N-methylaminobutyrate demethylating oxidase involved in catabolism of the tobacco alkaloid nicotine by Arthrobacter nicotinovorans pAO1

Nicotine catabolism, linked in Arthrobacter nicotinovorans to the presence of the megaplasmid pAO1, leads to the formation of gamma-N-methylaminobutyrate from the pyrrolidine ring of the alkaloid. Until now the metabolic fate of gamma-N-methylaminobutyrate has been unknown. pAO1 carries a cluster of ORFs with similarity to sarcosine and dimethylglycine dehydrogenases and oxidases, to the bifunctional enzyme methylenetetrahydrofolate dehydrogenase/cyclohydrolase and to formyltetrahydrofolate deformylase. We cloned and expressed the gene carrying the sarcosine dehydrogenase-like ORF and showed, by enzyme activity, spectrophotometric methods and identification of the reaction product as gamma-aminobutyrate, that the predicted 89 395 Da flavoprotein is a demethylating gamma-N-methylaminobutyrate oxidase. Site-directed mutagenesis identified His67 as the site of covalent attachment of FAD and confirmed Trp66 as essential for FAD binding, for enzyme activity and for the spectral properties of the wild-type enzyme. A Km of 140 microm and a kcat of 800 s(-1) was determined when gamma-N-methylaminobutyrate was used as the substrate. Sarcosine was also turned over by the enzyme, but at a rate 200-fold slower than gamma-N-methylaminobutyrate. This novel enzyme activity revealed that the first step in channelling the gamma-N-methylaminobutyrate generated from nicotine into the cell metabolism proceeds by its oxidative demethylation.

A novel tetrahydrofolate-dependent O-demethylase gene is essential for growth of Sphingomonas paucimobilis SYK-6 with syringate

Sphingomonas paucimobilis SYK-6 degrades syringate to 3-O-methylgallate (3MGA), which is finally converted to pyruvate and oxaloacetate via multiple pathways in which protocatechuate 4,5-dioxygenase, 3MGA dioxygenase, and gallate dioxygenase are involved. Here we isolated the syringate O-demethylase gene (desA), which complemented the growth deficiency on syringate of a Tn5 mutant of the SYK-6 derivative strain. The desA gene is located 929 bp downstream of ferA, encoding feruloyl-coenzyme A synthetase, and consists of a 1,386-bp open reading frame encoding a polypeptide with a molecular mass of 50,721 Da. The deduced amino acid sequence of desA showed 26% identity in a 325-amino-acid overlap with that of gcvT of Escherichia coli, which encodes the tetrahydrofolate (H(4)folate)-dependent aminomethyltransferase involved in glycine cleavage. The cell extract of E. coli carrying desA converted syringate to 3MGA only when H(4)folate was added to the reaction mixture. DesA catalyzes the transfer of the methyl moiety of syringate to H(4)folate, forming 5-methyl-H(4)folate. Vanillate and 3MGA were also used as substrates for DesA; however, the relative activities toward them were 3 and 0.4% of that toward syringate, respectively. Disruption of desA in SYK-6 resulted in a growth defect on syringate but did not affect growth on vanillate, indicating that desA is essential to syringate degradation. In a previous study the ligH gene, which complements the growth deficiency on vanillate and syringate of a chemical-induced mutant of SYK-6, DC-49, was isolated (S. Nishikawa, T. Sonoki, T. Kasahara, T. Obi, S. Kubota, S. Kawai, N. Morohoshi, and Y. Katayama, Appl. Environ. Microbiol. 64:836-842, 1998). Disruption of ligH resulted in the same phenotype as DC-49; its cell extract, however, was found to be able to convert vanillate and syringate in the presence of H(4)folate. The possible role of ligH is discussed.

Mammalian Electron Transferring Flavoprotein·Flavoprotein Dehydrogenase Complexes Observed by Microelectrospray Ionization-Mass Spectrometry and Surface Plasmon Resonance

Microelectrospray ionization-mass spectrometry was used to directly observe electron transferring flavoprotein.flavoprotein dehydrogenase interactions. When electron transferring flavoprotein and porcine dimethylglycine dehydrogenase or sarcosine dehydrogenase were incubated together in the absence of substrate, a relative molecular mass corresponding to the flavoprotein.electron transferring flavoprotein complex was observed, providing the first direct observation of these mammalian complexes. When an acyl-CoA dehydrogenase family member, human short chain acyl-CoA dehydrogenase, was incubated with dimethylglycine dehydrogenase and electron transferring flavoprotein, the microelectrospray ionization-mass spectrometry signal for the dimethylglycine dehydrogenase.electron transferring flavoprotein complex decreased, indicating that the acyl-CoA dehydrogenases have the ability to compete with the dimethylglycine dehydrogenase/sarcosine dehydrogenase family for access to electron transferring flavoprotein. Surface plasmon resonance solution competition experiments revealed affinity constants of 2.0 and 5.0 microm for the dimethylglycine dehydrogenase-electron transferring flavoprotein and short chain acyl-CoA dehydrogenase-electron transferring flavoprotein interactions, respectively, suggesting the same or closely overlapping binding motif(s) on electron transferring flavoprotein for dehydrogenase interaction.

Glycine transporter I inhibitor, N-methylglycine (sarcosine), added to antipsychotics for the treatment of schizophrenia

BACKGROUND

Hypofunction of N-methyl-D-aspartate glutamate receptor had been implicated in the pathophysiology of schizophrenia. Treatment with D-serine or glycine, endogenous full agonists of the glycine site of N-methyl-D-aspartate receptor, or D-cycloserine, a partial agonist, improve the symptoms of schizophrenia. N-methylglycine (sarcosine) is an endogenous antagonist of glycine transporter-1, which potentiates glycine's action on N-methyl-D-aspartate glycine site and can have beneficial effects on schizophrenia.

METHODS

Thirty-eight schizophrenic patients were enrolled in a 6-week double-blind, placebo-controlled trial of sarcosine (2 g/d), which was added to their stable antipsychotic regimens. Twenty of them received risperidone. Measures of clinical efficacy and side effects were determined every other week.

RESULTS

Patient who received sarcosine treatment revealed significant improvements in their positive, negative, cognitive, and general psychiatric symptoms. Similar therapeutic effects were observed when only risperidone-treated patients were analyzed. Sarcosine was well-tolerated, and no significant side effect was noted.

CONCLUSIONS

Sarcosine treatment can benefit schizophrenic patients treated by antipsychotics including risperidone. The significant improvement with the sarcosine further supports the hypothesis of N-methyl-D-aspartate receptor hypofunction in schizophrenia. Glycine transporter-1 is a novel target for the pharmacotherapy to enhance N-methyl-D-aspartate function.

Sequence of the 165-kilobase catabolic plasmid pAO1 from Arthrobacter nicotinovorans and identification of a pAO1-dependent nicotine uptake system

The 165-kb catabolic plasmid pAO1 enables the gram-positive soil bacterium Arthrobacter nicotinovorans to grow on the tobacco alkaloid L-nicotine. The 165,137-nucleotide sequence, with an overall G+C content of 59.7%, revealed, besides genes and open reading frames (ORFs) for nicotine degradation, a complete set of ORFs for enzymes essential for the biosynthesis of the molybdenum dinucleotide cofactor, as well as ORFs related to uptake and utilization of carbohydrates, sarcosine, and amino acids. Of the 165 ORFs, approximately 50% were related to metabolic functions. pAO1 conferred to A. nicotinovorans the ability to take up L-[(14)C]nicotine from the medium, with an K(m) of 5.6 +/- 2.2 micro M. ORFs of putative nicotine transporters formed a cluster with the gene of the D-nicotine-specific 6-hydroxy-D-nicotine oxidase. ORFs related to replication, chromosome partitioning, and natural transformation functions (dprA) were identified on pAO1. Few ORFs showed similarity to known conjugation-promoting proteins, but pAO1 could be transferred by conjugation to a pAO1-negative strain at a rate of 10(-2) to 10(-3) per donor. ORFs with no known function represented approximately 35% of the pAO1 sequence. The positions of insertion sequence elements and composite transposons, corroborated by the G+C content of the pAO1 sequence, suggest a modular composition of the plasmid.

Organization of the genes involved in dimethylglycine and sarcosine degradation in Arthrobacter spp.: implications for glycine betaine catabolism

The nucleotide sequences of two cloned DNA fragments containing the structural genes of heterotetrameric sarcosine oxidase (soxBDAG) and dimethylglycine dehydrogenase (dmg) from Arthrobater spp. 1-IN and Arthrobacter globiformis, respectively, have been determined. Open reading frames were identified in the soxBDAG operon corresponding to the four subunits of heterotetrameric sarcosine oxidase by comparison with the N-terminal amino-acid sequences and the subunit relative molecular masses of the purified enzyme. Alignment of the deduced sarcosine oxidase amino-acid sequence with amino-acid sequences of functionally related proteins indicated that the arthrobacterial enzyme is highly homologous to sarcosine oxidase from Corynebacterium P-1. Deletion and expression analysis, and alignment of the deduced amino-acid sequence of the dmg gene, showed that dmg encodes a novel dimethylglycine oxidase, which is related to eukaryotic dimethylglycine dehydrogenase, and contains nucleotide-binding, flavinylation and folate-binding motifs. The recombinant dimethylglycine oxidase was purified to homogeneity and characterized. The DNA located upstream and downstream of both the soxBDAG and dmg genes is predicted to encode enzymes involved in the tetrahydrofolate-dependent assimilation of methyl groups. Based on the sequence analysis reported herein, pathways are proposed for glycine betaine catabolism in Arthrobacter species, which involve the identified folate-dependent enzymes.

Cloning of dimethylglycine dehydrogenase and a new human inborn error of metabolism, dimethylglycine dehydrogenase deficiency

Dimethylglycine dehydrogenase (DMGDH) (E.C. number 1.5.99.2) is a mitochondrial matrix enzyme involved in the metabolism of choline, converting dimethylglycine to sarcosine. Sarcosine is then transformed to glycine by sarcosine dehydrogenase (E.C. number 1.5.99.1). Both enzymes use flavin adenine dinucleotide and folate in their reaction mechanisms. We have identified a 38-year-old man who has a lifelong condition of fishlike body odor and chronic muscle fatigue, accompanied by elevated levels of the muscle form of creatine kinase in serum. Biochemical analysis of the patient's serum and urine, using (1)H-nuclear magnetic resonance NMR spectroscopy, revealed that his levels of dimethylglycine were much higher than control values. The cDNA and the genomic DNA for human DMGDH (hDMGDH) were then cloned, and a homozygous A-->G substitution (326 A-->G) was identified in both the cDNA and genomic DNA of the patient. This mutation changes a His to an Arg (H109R). Expression analysis of the mutant cDNA indicates that this mutation inactivates the enzyme. We therefore confirm that the patient described here represents the first reported case of a new inborn error of metabolism, DMGDH deficiency.

Association of betaine-homocysteine S-methyltransferase with microtubules

In mammals, betaine of the mitochondrial matrix is used in the cytosol by betaine-homocysteine S-methyltransferase for methionine synthesis. The resulting dimethylglycine is shuttled back into the mitochondrial matrix for further degradation. Nanospray tandem mass spectrometry and N-terminal amino acid sequencing of microtubule-associated proteins from rat liver tubulin revealed that betaine-homocysteine S-methyltransferase is microtubule associated. This was confirmed by confocal laser scanning microscopy of HepG2 cells labeled with betaine-homocysteine S-methyltransferase- and alpha-tubulin-specific monoclonal antibodies. The association of betaine-homocysteine S-methyltransferase with the cytoskeleton may functionally integrate the mitochondrial and cytoplasmic compartments of choline degradation.

Structure and analysis of the human dimethylglycine dehydrogenase gene

Dimethylglycine dehydrogenase (DMGDH; E.C. 1.5.99.2) is an enzyme involved in the catabolism of choline, catalyzing the oxidative demethylation of dimethylglycine (DMG) to form sarcosine. Subsequently, sarcosine dehydrogenase (SDH; E.C. 1.5.99.1) converts sarcosine to glycine via a similar reaction. Both enzymes are found as monomers in the mitochondrial matrix, and both contain 1 mol of covalently bound flavin adenine dinucleotide. DMGDH and SDH also utilize a noncovalently bound folate coenzyme that receives the "1-carbon" groups that are removed by DMGDH and SDH, forming "active formaldehyde." We have recently described a new inborn error of metabolism of DMGDH characterized by an unusual fish-like body odor. To augment our study of this new disorder, we have isolated two human genomic clones that together contain 16 exons of coding sequence for the hDMGDH gene. Fluorescent in situ hybridization analysis of the hDMGDH gene indicates that it is found on chromosome 5q12.2-q12.3. In addition, several polymorphisms have been identified in the hDMGDH cDNA sequence. Population analysis of two Ser/Pro polymorphisms found 367 amino acids apart reveals a skew of alleles, with the haplotypes Ser/Pro or Pro/Ser (79%) overrepresented compared to the number of Ser/Ser or Pro/Pro alleles observed. Possible functional consequences of these findings are discussed. Characterization of the gene structure for hDMGDH will aid in the study of patients with inherited defects of this enzyme.

Cloning and mapping of the cDNA for human sarcosine dehydrogenase, a flavoenzyme defective in patients with sarcosinemia

Sarcosine dehydrogenase is a liver mitochondrial matrix flavoenzyme that is defective in patients with sarcosinemia, a rare autosomal metabolic defect characterized by elevated levels of sarcosine in blood and urine. Some patients also exhibit mental retardation and growth failure. A full-length cDNA for human sarcosine dehydrogenase was isolated from an adult liver cDNA library. The first 22 residues in the deduced amino acid sequence exhibit features expected for a mitochondrial targeting sequence. The predicted mass of the mature human liver sarcosine dehydrogenase (99,505 Da) is in good agreement with that observed for rat liver sarcosine dehydrogenase ( approximately 100,000 Da). Human sarcosine dehydrogenase exhibits 89% identity with rat liver sarcosine dehydrogenase and strong homology ( approximately 35% identity) with rat liver dimethylglycine dehydrogenase, a sarcosine dehydrogenase-related protein from Rhodobacter capsulatus, and the regulatory subunit from bovine pyruvate dehydrogenase phosphatase. The human sarcosine dehydrogenase gene is at least 75.3 kb long and located on chromosome 9q34. The adult human liver clone is assembled from 21 exons (1-6, 7a, 8a, 9-21). Two smaller cDNA clones, isolated from adult liver and infant brain libraries, were assembled from the same sarcosine dehydrogenase gene by the use of alternate polyadenylation and splice sites. This is the first report of the genomic structure of the sarcosine dehydrogenase gene in any species. The observed chromosomal location is consistent with genetic studies with a mouse model for sarcosinemia that map the mouse gene to a region of mouse chromosome 2 syntenic with human 9q33-q34. The availability of the SDH gene sequence will enable characterization of the genotypes of sarcosinemia patients with different phenotypes.