bluuebunny/crossref_metadata_2025 huggingface dataset:
Low salt intake modulates insulin signaling, JNK activity and IRS-1ser307 phosphorylation in rat tissues
Authors: Prada Patrícia Oliveira , Coelho Michella Soares , Zecchin Henrique Gottardello , Dolnikoff Miriam Sterman , Gasparetti Alessandra Lia , Furukawa Luzia Naôko Shinohara , Saad Mario José Abdalla , Heimann Joel Claudio
Published: June 2005

A severe restriction of sodium chloride intake has been associated with insulin resistance and obesity. The molecular mechanisms by which the low salt diet (LS) can induce insulin resistance have not yet been established. The c-jun N-terminal kinase (JNK) activity has been involved in the pathophysiology of obesity and induces insulin resistance by increasing inhibitory IRS-1ser307 phosphorylation. In this study we have evaluated the regulation of insulin signaling, JNK activation and IRS-1ser307 phophorylation in liver, muscle and adipose tissue by immunoprecipitation and immunoblotting in rats fed with LS or normal salt diet (NS) during 9 weeks. LS increased body weight, visceral adiposity, blood glucose and plasma insulin levels, induced insulin resistance and did not change blood pressure. In LS rats a decrease in PI3-K/Akt was observed in liver and muscle and an increase in this pathway was seen in adipose tissue. JNK activity and IRS-1ser307 phosphorylation were higher in insulin-resistant tissues. In summary, the insulin resistance, induced by LS, is tissue-specific and is accompanied by activation of JNK and IRS-1ser307 phosphorylation. The impairment of the insulin signaling in these tissues, but not in adipose tissue, may lead to increased adiposity and insulin resistance in LS rats.
Increased oxygen consumption rates in response to high glucose detected by a novel oxygen biosensor system in non-human primate and human islets
Authors: Wang Wenjing , Upshaw Lisa , Strong D Michael , Robertson R Paul , Reems JoAnna
Published: June 2005

In this study, we investigated the use of a novel oxygen biosensor system to detect changes in oxygen consumption rates (OCRs) by islets in response to glucose. Islets from non-human primate and human pancreata were seeded into an oxygen biosensor system microplate and exposed to basal (2.8 or 5.6 mM) or high (16.7 or 33.3 mM) glucose over either a long-term or a short-term culture. Our data clearly demonstrated that non-human primate islets cultured in high glucose conditions exhibited significant increases in OCRs over a 168 h extended culture period (P<0.05), which indicates an accelerated rate of β-cell metabolism triggered by glucose over time. Significant increases in OCRs (P<0.01) were also attained in both non-human primate and human islets exposed to high glucose conditions in a 120 min short-term incubation period. OCRs exhibited by human islets exposed to different glucose concentrations correlated with insulin secretion (r2=0.7681, P<0.01). Moreover, the OCR stimulation index (i.e. OCR at high glucose/OCR at basal glucose) was significantly greater in human islets displaying high viabilities as opposed to islets exhibiting low viabilities (P<0.05). Together these data demonstrate that this novel oxygen biosensor system documents significant increases in islet oxygen consumption upon acute and chronic exposure to high glucose concentrations. Importantly, this methodology rapidly and robustly detects changes in OCRs by islets in response to high glucose stimulation that correlate well with the metabolic activities and functional viability of islets and clearly delineates significant differences in OCR stimulation index between high and low viability human islets, and therefore may prove to be an effective approach for quickly assessing the functional viability of islets prior to transplantation.
Induction of pancreatic acinar cell proliferation by thyroid hormone
Authors: Ledda-Columbano G M , Perra A , Pibiri M , Molotzu F , Columbano A
Published: June 2005

Thyroid hormone is known to elicit diverse cellular and metabolic effects in various organs, including mitogenesis in the rat liver. In the present study, experiments were carried out to determine whether thyroid hormone is able to stimulate cell proliferation in another quiescent organ such as the pancreas. 3,5,3′-l-tri-iodothyronine (T3) added to the diet at a concentration of 4 mg/kg caused a striking increase in nuclear bromodeoxyuridine (BrdU) incorporation of rat acinar cells 7 days after treatment (the labeling index was 46.7% in T3-treated rats vs 7.1% in controls). BrdU incorporation was limited to the acinar cells, with duct cells and islet cells being essentially negative. The increase in DNA synthesis was accompanied by the presence of several mitotic figures. Histological examination of the pancreas did not exhibit any sign of T3-induced toxicity. Determination of the apoptotic index, measurement of the serum levels of α-amylase and lipase, and glycemia determination did not show any increase over control values, suggesting that the enhanced proliferation of acinar cells was a direct effect induced by T3 and not a regenerative response consequent to acinar or β-cell injury. Additional experiments showed that DNA synthesis was induced as early as 2 days after T3 treatment (the labeling index was 9.4 vs 1.9% in controls) and was associated with increased protein levels of cyclin D1, cyclin A and proliferating cell nuclear antigen, with no substantial differences in the expression of the cyclin-dependent kinase inhibitor p27. The mitogenic effect of T3 on the pancreas was not limited to the rat, since extensive acinar cell proliferation was also observed in the pancreas of mice treated with T3 for 1 week (the labeling index was 28% in T3-treated mice vs 1.8% in controls). Treatment with three other ligands of nuclear receptors, ciprofibrate, all-trans retinoic acid and 1,4-bis[2-(3,5-dichloropyridyloxy)]benzene, induced little or no pancreatic cell proliferation. These results demonstrated that T3 is a powerful inducer of cell proliferation in the pancreas and suggested that pancreatic acinar cell proliferation by selected agents may have potential for therapeutic use.
The E23K variant in the Kir6.2 subunit of the ATP-sensitive K+ channel does not augment impaired glucose tolerance in Caribbean subjects with a family history of type 2 diabetes
Authors: Ezenwaka Chidum , Kalloo Risha , Uhlig Mathias , Schwenk Robert , Eckel Juergen
Published: June 2005

The E23K variant of the Kir6.2 gene has been shown to be associated with type 2 diabetes mellitus in Caucasian subjects. Because offspring of type 2 diabetic patients have a genetically increased risk of developing diabetes, we sought to identify the E23K variant of the Kir6.2 gene in offspring of Caribbean patients with type 2 diabetes and assess the contribution of this variant to impaired glucose tolerance in these subjects. Forty-six offspring of patients with type 2 diabetes and 39 apparently healthy subjects whose immediate parents were not diabetic (‘control’) were studied after an overnight fast. Anthropometric indices were measured and blood samples were collected. Fasting and 2 h plasma glucose, insulin and lipids were subsequently determined. Insulin resistance was calculated using the homeostatic model assessment technique. The offspring and control subjects had similar frequencies of the E23K polymorphism (52.6 vs 45.5%, P>0.05) and the frequency of the E23K variant did not differ significantly between gender and ethnic distributions, irrespectively of a family history of diabetes (P>0.05). There were no significant differences in biochemical risk factors for developing diabetes in offspring carriers of the E23K variant compared with offspring non-carriers of the mutation. Offspring with the E23K mutation had even significantly higher 2 h insulin concentrations when compared with control subjects. It is concluded that the presence of the Kir6.2 E23K genotype in Caribbean subjects with an immediate positive family history of diabetes does not confer significantly higher levels of biochemical risk factors for the development of type 2 diabetes.
Effects of histone deacetylase inhibitors on estradiol-induced proliferation and hyperplasia formation in the mouse uterus
Authors: Gunin Andrei G , Kapitova Irina N , Suslonova Nina V
Published: June 2005

It is suggested that estrogen hormones recruit mechanisms controlling histone acetylation to bring about their effects in the uterus. However, it is not known how the level of histone acetylation affects estrogen-dependent processes in the uterus, especially proliferation and morphogenetic changes. Therefore, this study examined the effects of histone deacetylase blockers, trichostatin A and sodium butyrate, on proliferative and morphogenetic reactions in the uterus under long-term estrogen treatment. Ovari-ectomized mice were treated with estradiol dipropionate (4 μg per 100 g; s.c., once a week) or vehicle and trichostatin A (0.008 mg per 100 g; s.c., once a day) or sodium butyrate (1% in drinking water), or with no additional treatments for a month. In animals treated with estradiol and trichostatin A or sodium butyrate, uterine mass was increased, and abnormal uterine glands and atypical endometrial hyperplasia were found more often. Both histone deacetylase inhibitors produced an increase in the numbers of mitotic and bromodeoxyuridine-labelled cells in luminal and glandular epithelia, in stromal and myometrial cells. Levels of estrogen receptor-α and progesterone receptors in uterine epithelia, stromal and myometrial cells were decreased in mice treated with estradiol and trichostatin A or sodium butyrate. Expression of β-catenin in luminal and glandular epithelia was attenuated in mice treated with estradiol with trichostatin A or sodium butyrate. Both histone deacetylase inhibitors have similar unilateral effects; however the action of trichostatin A was more expressed than that of sodium butyrate. Thus, histone deacetylase inhibitors exert proliferative and morphogenetic effects of estradiol. The effects of trichostatin A and sodium butyrate are associated with changes in expression of estrogen receptor-α, progesterone receptors and β-catenin in the uterus.
α2-Macroglobulin expression in the liver in response to inflammation is mediated by the testis
Authors: Lui Wing-Yee , Cheng Yan Ho , Mruk Dolores D , Cheng Chin Ho , Mo Meng Yun , Lee Will M , Cheng C Yan
Published: June 2005

Earlier studies have shown that germ cells or germ cell-conditioned media are capable of regulating α2-macroglobulin (α2-MG, a non-specific protease inhibitor) expression by Sertoli cells and hepatocytes cultured in vitro. These results illustrate a possible physiological link between testes and liver regarding α2-MG production. Using a series of surgical procedures including castration, hemicastration, and hepatectomy coupled with Northern blot and immunoblot analyses, we report herein that the surge in α2-MG expression in the liver in response to inflammation is indeed regulated, at least in part, by the testis via testosterone. It was found that hepatectomy induced at least a tenfold increase in the steady-state mRNA and protein production of α2-MG in the liver. However, castration induced a mild but not statistically significant induction of α2-MG in the liver in contrast to sham operation or hemicastration alone, when hemicastration alone could induce liver α2-MG production by almost fourfold. Perhaps most important of all, hepatectomy accompanied by castration significantly reduced the liver α2-MG response to the surgery-induced inflammation compared with hepatectomy alone, illustrating that the removal of the testicles can induce a loss of signal communications between the testis and the liver, rendering a significant loss of the α2-MG response to experimentally induced inflammation in the liver. Interestingly, this lack of response of the liver to surgery-induced inflammation regarding α2-MG production following castration could be restored, at least in part, by using testosterone implants placed subdermally 6 days prior to orchiectomy. Collectively, these results illustrate that a physiological link does indeed exist between the testis and the liver, and that testes per se can influence the liver in vivo α2-MG expression in response to inflammation possibly via testosterone or testosterone-induced biological factor(s).
Impaired skeletal growth in mice with haploinsufficiency of IGF-I: genetic evidence that differences in IGF-I expression could contribute to peak bone mineral density differences
Authors: Mohan S , Baylink D J
Published: June 2005

Although it is well established that there is considerable inter-individual variation in the circulating levels of IGF-I in normal, healthy individuals and that a genetic component contributes substantially to this variation, the direct evidence that inter-individual variation in IGF-I contributes to differences in peak bone mineral density (BMD) is lacking. To examine if differences in IGF-I expression could contribute to peak BMD differences, we measured skeletal changes at days 23 (prepubertal), 31 (pubertal) and 56 (postpubertal) in mice with haploinsufficiency of IGF-I (+/−) and corresponding control mice (+/+). Mice (MF1/DBA) heterozygous for the IGF-I knockout allele were bred to generate +/+ and +/− mice (n=18–20 per group). Serum IGF-I was decreased by 23% (P<0.001) in mice with IGF-I haploinsufficiency (+/−) group at day 56 compared with the control (+/+) group. Femoral bone mineral content and BMD, as determined by dual energy X-ray absorptiometry, were reduced by 20% (P<0.001) and 12% respectively in the IGF-I (+/−) group at day 56 compared with the control group. The peripheral quantitative computed tomography measurements at the femoral mid-diaphysis revealed that periosteal circumference (7%, P<0.01) and total volumetric BMD (5%, P<0.05) were decreased significantly in the +/− group compared with the +/+ group. Furthermore, serum IGF-I showed significant positive correlations with both areal BMD (r=0.55) and periosteal circumference (r=0.66) in the pooled data from the +/+ and +/− groups. Our findings that haploinsufficiency of IGF-I caused significant reductions in serum IGF-I level, BMD and bone size, together with the previous findings, are consistent with the notion that genetic variations in IGF-I expression could, in part, contribute to inter-individual differences in peak BMD among a normal population.
Hormonal regulation of the novel adipocytokine visfatin in 3T3-L1 adipocytes
Authors: Kralisch Susan , Klein Johannes , Lossner Ulrike , Bluher Matthias , Paschke Ralf , Stumvoll Michael , Fasshauer Mathias
Published: June 2005

Recently, visfatin was characterized as a novel adipo-cytokine that is upregulated in obesity and exerts insulin-mimetic effects in various tissues. To clarify expression and regulation of this adipocytokine, visfatin mRNA was measured by quantitative real-time reverse transcription-polymerase chain reaction in 3T3-L1 adipocytes during adipogenesis and after treatment with various hormones known to alter insulin sensitivity. Visfatin expression was about 6-fold higher in 3T3-L1 adipocytes in vitro as compared with epididymal fat in vivo and increased during adipogenic conversion more than 3-fold. Interestingly, 100 nM dexamethasone significantly increased visfatin mRNA by almost 1.5-fold. In contrast, 500 ng/ml growth hormone (GH), 10 ng/ml tumor necrosis factor (TNF) α, and 10 μM isoproterenol downregulated visfatin expression by 45%, 36%, and 43% respectively. Insulin did not influence synthesis of this adipocytokine. The effects of dexamethasone, GH, TNFα and isoproterenol were time- and dose-dependent. Furthermore, activation of Gs-protein-coupled pathways by forskolin and cholera toxin was sufficient to significantly downregulate visfatin mRNA. Taken together, our results show a differential regulation of visfatin mRNA by insulin resistance-inducing hormones, supporting the view that this adipo-cytokine might be an interesting novel candidate linking core components of the metabolic syndrome such as obesity and insulin resistance.
The Substrate Spectrum of Mandelate Racemase: Minimum Structural Requirements for Substrates and Substrate Model
Authors: Felfer Ulfried , Goriup Marian , Koegl Marion F. , Wagner Ulrike , Larissegger‐Schnell Barbara , Faber Kurt , Kroutil Wolfgang
Published: June 2005

Mandelate racemase (EC 5.1.2.2) is one of the few biochemically well‐characterized racemases. The remarkable stability of this cofactor‐independent enzyme and its broad substrate tolerance make it an ideal candidate for the racemization of non‐natural α‐hydroxycarboxylic acids under physiological reaction conditions to be applied in deracemization protocols in connection with a kinetic resolution step. This review summarizes all aspects of mandelate racemase relevant for the application of this enzyme in preparative‐scale biotransformations with special emphasis on its substrate tolerance. Collection and evaluation of substrate structure‐activity data led to a set of general guidelines, which were used as basis for the construction of a general substrate model, which allows a quick estimation of the expected activity for a given substrate.
Microbial Reduction and in situ Product Crystallization Coupled with Biocatalyst Cultivation during the Synthesis of 6R‐Dihydrooxoisophorone
Authors: Buque‐Taboada Evelyn M. , Straathof Adrie J. J. , Heijnen Joseph J. , van der Wielen Luuk A. M.
Published: June 2005

An in situ product crystallization procedure was developed for a crystalline product formed during microbial reduction coupled with cell cultivation. The model reaction was the asymmetric reduction of 4‐oxoisophorone (OIP) by baker's yeast (Saccharomyces cerevisiae). Yeast cells were cultivated fed‐batch to reach a maximum concentration of 30 gdw⋅L−1. The desired product, 6R‐dihydrooxoisophorone (DOIP), may be further reduced by baker's yeast to an unwanted by‐product; thus, DOIP was removed immediately from the fermenter via an external crystallization loop in this procedure. The OIP reduction rate was five times higher (≅0.33 mmol⋅gdw−1⋅h−1) as compared to the reduction rate with resting cells. OIP reduction was started when the optimum cell concentration had already been reached in the reactor because the substrate (OIP) at ≥55 mM concentration inhibited cell growth. An appropriate supply of glucose as carbon and energy source was necessary to support the coupled reactions involving cell growth and maintenance and product formation while avoiding formation of metabolic by‐products. Final DOIP yield and selectivity were 85% and 99%, respectively, while over 100 g⋅L−1 of product was obtained in the crystallizer. The product crystals with favorable properties were readily recovered from the crystallizer. These results indicate that product crystallization is not impaired by the solutes present in the fermentation medium.
Study of the Chemoselectivity in the Aminolysis Reaction of Methyl Acrylate Catalysed by Lipase B from Candida antarctica
Authors: Torre Oliver , Gotor‐Fernández Vicente , Alfonso Ignacio , García‐Alles Luis Fernando , Gotor Vicente
Published: June 2005

The aminolysis reaction of methyl acrylate (MA) with N,N‐dimethyl‐1,3‐propanediamine (DMAPA) in organic solvents has been optimised using lipase B from Candida antarctica (CAL‐B) as biocatalyst. A kinetic study about the influence of the reactant concentrations, organic solvent, temperature and enzyme form has been developed focused on minimising the formation of the Michael addition products. The economic efficiency of this process has been finally investigated by reusing the enzyme in the best reaction conditions, thereby observing no significant loss of activity after three reaction cycles.
Asymmetric Synthesis of L‐α‐Methylcysteine with the Amidase from Xanthobacter flavus NR303
Authors: Inoue Atsushi , Komeda Hidenobu , Asano Yasuhisa
Published: June 2005

An amidase acting on d, l‐α‐methylcysteinamide was purified from Xanthobacter flavus NR303. The enzyme acted L‐stereoselectively on d,l‐α‐methylcysteinamide to yield L‐α‐methylcysteine. Based on the N‐terminal amino acid sequence of the amidase, the gene encoding the enzyme was cloned from the genomic DNA of X. flavus and sequenced. Analysis of 4840 bp of the genomic DNA revealed the presence of an open reading frame (mcaA) which encodes the amidase. This enzyme is composed of 355 amino acid residues (molecular mass, 38555 Da). The intact cells of the Escherichia coli transformant could be used for the L‐stereoselective hydrolysis of racemic α‐methylcysteinamide. It was activated in the presence of Mn2+, and had maximal activity at pH 7.0 and 55 °C. The E. coli transformant catalyzed the synthesis of L‐α‐methylcysteine from d, l‐α‐methylcysteinamide in a yield of 80% with high optical purity (>98% ee).
FADH2‐Dependence of Tryptophan 7‐Halogenase
Authors: Unversucht Susanne , Hollmann Frank , Schmid Andreas , van Pée Karl‐Heinz
Published: June 2005

Tryptophan 7‐halogenase (Trp 7‐hal) catalyses the regioselective chlorination and bromination of tryptophan. For halogenating activity, Trp 7‐hal requires FADH2 produced from FAD and NADH by a flavin reductase, halide ions (chloride or bromide), molecular oxygen and tryptophan as the organic substrate. Investigations of the flavin dependence showed that purified Trp 7‐hal itself does not contain flavin. Keeping the Trp 7‐hal separated from the flavin reductase during the reaction revealed that Trp 7‐hal can use diffusible FADH2 produced by a flavin reductase showing that direct contact between the halogenase and the flavin reductase is not absolutely necessary. Thus, the reaction also proceeds when chemically reduced flavin is used. For the catalytic regeneration of FADH2, the organometallic complex (pentamethylcyclopentadienyl)rhodium‐bipyridine {[Cp*Rh(bpy)(H2O)]2+} can be employed as the redox catalyst with formate as the electron donor. With this chemoenzymatic system about 85% yields of the product formed by the two‐component enzyme system consisting of Trp 7‐hal and a flavin reductase were obtained.
Peroxidase‐Catalyzed Coupling of Solid‐Supported ortho‐Methoxyphenols
Authors: Antoniotti Sylvain , Dordick Jonathan S.
Published: June 2005

Enzyme‐catalyzed CC bond formation has been performed on solid‐supported phenols, thereby expanding the repertoire of enzymatic catalysis on resin‐bound substrates. In the presence of hydroquinone bound to various commercial resins, soybean peroxidase catalyzed the coupling of apocynin (acetovanillone) to give dimers, trimers, and oligomers with structures similar to what is obtained in solution‐phase reactions. In addition to phenolic coupling, peroxidase catalyzed a Fries rearrangement presumably due to rearrangement of the acyl phenolic radicals generated on the solid phase through peroxidase catalysis. This represents the first enzymatic Fries rearrangement reported to date. Together with the solid‐phase biocatalytic phenolic coupling, these results provide a route to the further expansion of enzymatic catalysis in combinatorial library synthesis.
A Fluorescence‐Based Assay for Baeyer–Villiger Monooxygenases, Hydroxylases and Lactonases
Authors: Sicard Renaud , Chen Lu S. , Marsaioli Anita J. , Reymond Jean‐Louis
Published: June 2005

Alkylation of umbelliferone and nitrophenol with chloroacetone, 3‐chlorobutanone, 2‐chlorocyclopentanone and 2‐chlorocyclohexanone gave the corresponding 2‐coumaryloxy and 2‐nitrophenoxy ketones. The 2‐coumaryloxy ketones were used as fluorogenic substrates to detect Baeyer–Villiger monooxygenases activities of microbial cultures in high‐throughput using microtiter plates. The 2‐coumaryloxy ketones were oxidized by microorganisms producing Baeyer–Villiger monooxygenases (BVMO), releasing umbelliferone as a fluorescent signal. The substrates were also biotransformed by a microbial monooxygenase (Trichosporon cutaneum). Chemical Baeyer–Villiger oxidation of 2‐coumaryloxy ketones using meta‐chloroperbenzoic acid proceeded regioselectively to the corresponding acyloxyalkyl derivatives of umbelliferone and nitrophenol. These chiral lactones underwent a fluorogenic and chromogenic reaction upon hydrolysis by esterases, in particular pig liver esterase. Enantioselectivity of the ester hydrolysis reaction was determined by chiral‐phase analysis of the unreacted lactones.
Multienzyme Profiling of Thermophilic Microorganisms with a Substrate Cocktail Assay
Authors: Sicard Renaud , Goddard Jean‐Philippe , Mazel Magali , Audiffrin Carine , Fourage Laurent , Ravot Gilles , Wahler Denis , Lefèvre Fabrice , Reymond Jean‐Louis
Published: June 2005

Labeled substrates for 16 different catalytic activities were combined into a cocktail reagent for multienzyme functional profiling, called PHENOZYMTM. The assay involves a single reaction followed by determination of substrate consumption by HPLC‐analysis. The method allows a rapid identification of multiple enzyme activities, and is compatible with a diversity of growth media and reaction conditions (pH, temperature). The PHENOZYMTM cocktail was used to analyze the activity of 16 enzyme activities in a series of microbial strains, including thermophilic microorganisms. The functional profiles were used for a functional classification of the different microbial strains tested by hierarchical cluster analysis. The resulting “phylo‐enzymatic” tree revealed associations consistent with the known phylogenetic classification of the strains. The influence of the culture medium on the enzyme activity profiles was also apparent.
Synthesis of Sialyl TN Glycopeptides – Enzymatic Sialylation by α2,6‐Sialyltransferase from Photobacterium damsela
Authors: Teo Chin‐Fen , Hwang Tzann‐Shun , Chen Pei‐Heng , Hung Chih‐Hung , Gao Heau‐Shan , Chang Lee‐Shang , Lin Chun‐Hung
Published: June 2005

The α2,6‐sialyltransferase from Photobacterium damsela was applied for the enzymatic sialylation of the TN glycopeptide (APGSTA) with GalNAc α‐linked to either the serine or threonine residue in the sequence. The enzyme preparation and reaction conditions were optimized prior to the application. In contrast to the mammalian sialyltransferases which recognize the moiety of GalNAcα(1,1)Thr only, this bacterial enzyme can accept GalNAcα(1,1)Thr as well as GalNAcα(1,1)Ser. Our study also introduced a 4‐dimethylaminoazobenzene‐4′‐sulfonyl (dabsyl) chromophore to the N‐terminus of the peptide backbone, which is suitable for glycoconjugate substrates without affecting the binding affinity
Current and Emerging Approaches for Natural Product Biosynthesis in Microbial Cells
Authors: Watts Kevin T. , Mijts Benjamin N. , Schmidt‐Dannert Claudia
Published: June 2005

Microorganisms and plants synthesize a tremendous diversity of chemical compounds. For centuries, these compounds have been used as medicines, foods and other useful materials. The still largely unexplored structural and chemical diversity of natural products is unmatched by synthetic methodology and continues to be the most successful source for the discovery of novel scaffolds with important biological activities. Thus, exploiting the selectivity and specificity of the biosynthetic machineries that make these complex compounds can provide ways of synthesizing diverse natural products or their core scaffolds for further synthetic modification. Microbial cells can be fitted with new biosynthetic abilities using metabolic and genetic engineering strategies to overproduce desired compounds. Efforts in genome sequencing give access to an incredible number of genes from microorganisms and, more recently, from plants that can be in silico screened for new biosynthetic functions allowing tapping into the synthetic potential of microorganisms, and especially plants. In addition, by exploiting natural biodiversity by using traditional screening methods or metagenomics approaches, novel biosynthetic pathways and genes can be discovered for the synthesis of additional structures in engineered microbial cells. In this review, we will describe some of the recent developments in natural product biosynthesis, and also describe some of the emerging approaches to harness the chemical diversity that lies hidden in nature.
Comparison of Alkyl Hydroperoxide Reductase (AhpR) and Water‐Forming NADH Oxidase from Lactococcus lactis ATCC 19435
Authors: Jiang Rongrong , Riebel Bettina R. , Bommarius Andreas S.
Published: June 2005

We have successfully applied the sequence comparison‐based approach to develop a peroxidase (gene AhpC) and a water‐forming NADH oxidase from Lactococcus lactis (L. lactis). We found a considerably lower maximum specific activity of nox‐1 (AhpF) (15 U/mg) from L. lactis compared to its nox‐2 counterpart (95 U/mg). Both nox‐1 and nox‐2 are turnover‐limited, as expected for enzymes with labile, redox‐active thiols in the active site. In the absence of exogenously added thiols, both nox‐1 and nox‐1/peroxidase are considerably more stable against overoxidation than nox‐2: the total turnover number TTN is 82,000 for nox‐1 and nox‐1/peroxidase vs. 39,000 for nox‐2. Addition of exogenous thiols, however, increases nox‐2 stability by a factor of two, up to the level of nox‐1. Kinetic and stability analysis does not reveal any clear advantage for oxygen scavenging via the nox‐1 or the nox‐2 routes in lactic acid bacteria. Expression levels in lactic acid bacteria upon exposure to oxidative stress rather than kinetic performance more likely account for the previously observed superiority of nox‐2 effectiveness over nox‐1.
Converting Phenylacetone Monooxygenase into Phenylcyclohexanone Monooxygenase by Rational Design: Towards Practical Baeyer–Villiger Monooxygenases
Authors: Bocola Marco , Schulz Frank , Leca François , Vogel Andreas , Fraaije Marco W. , Reetz Manfred T.
Published: June 2005

A homology model of the most frequently used, but thermally somewhat labile, Baeyer–Villiger monooxygenase, cyclohexanone monooxygenase (CHMO) has been derived on the basis of the recently published crystal structure of the thermally stable phenylacetone monooxygenase (PAMO). This has led to the identification of a structural element crucial for substrate acceptance and stereoselectivity, namely an arginine‐interacting loop near the active site. A bulge in this loop occurring in PAMO (but not in CHMO) has been eliminated by mutation, enhancing the range of substrate acceptance and enantioselectivity of Baeyer–Villiger reactions while maintaining high thermal stability.
Regioselective Phosphorylation of Carbohydrates and Various Alcohols by Bacterial Acid Phosphatases; Probing the Substrate Specificity of the Enzyme from Shigella flexneri
Authors: van Herk Teunie , Hartog Aloysius F. , van der Burg Alida M. , Wever Ron
Published: June 2005

Bacterial non‐specific acid phosphatases normally catalyze the dephosphorylation of a variety of substrates. As shown previously the enzymes from Shigella flexneri and Salmonella enterica are also able to catalyze the phosphorylation of inosine to inosine monophosphate and D‐glucose to D‐glucose 6‐phosphate (D‐G6P) using cheap pyrophosphate as the phosphate donor. After optimization high yields (95%) are achieved in the latter reaction and we show here that it is possible to use these enzymes in a preparative manner. This prompted us to investigate by using 31P NMR and HPLC also the phosphorylation of a broad range of carbohydrates and alcohols. Many cyclic carbohydrates are phosphorylated in a regioselective manner. Non‐cyclic carbohydrates are phosphorylated as well. Phosphorylation of linear alcohols, cyclic and aromatic alcohols is also possible. In all cases the acid phosphatase from Shigella prefers a primary alcohol function above a secondary one. We conclude that these enzymes are an attractive alternative to existing chemical and enzymatic methods in the phosphorylation of a broad range of compounds.
Air pollution remediation in a fixed bed photocatalytic reactor coated with TiO2
Authors: Esterkin C. R. , Negro A. C. , Alfano O. M. , Cassano A. E.
Published: June 2005

In a previous article, the modeling and experimental verification of the radiation field inside a reactor made of several TiO2 coated, parallel, flat glass fiber meshes, bilaterally UV irradiated was accomplished. The degradation of trichloroethylene (TCE) in an air stream is studied using different values of the pollutant feed concentration, relative humidity and light intensity under operating conditions where kinetic control of the process is established. A kinetic model based on a reaction scheme that involves atomic chlorine as an active reaction intermediate is developed for describing concentration dependencies. It includes, explicitly, the effect of the absorbed light intensity on the rate. The interaction of the existing radiation field with the solid semiconductor to generate electrons, and holes in the reaction catalyst activation step is also modeled. All kinetic parameters are estimated from experiments. The obtained kinetic expression gives a first‐order dependence with respect to the TCE concentration and accounts for a competitive effect of water vapor and TCE for the catalyst active sites. An additional important feature of the derived expression is its ability to represent both limiting cases concerning the dependence of the reaction rate with the irradiation rate; that is, order 1 or order 0.5, as well as all possible intermediate values. In fact, the equivalent dependence obtained in this work was 0.6, a value closer to the second case. The results show good agreement between predictions derived from the proposed kinetic expression and TCE experimental concentration data at the reactor's exit. The proposed reactor design provides a practical device for the treatment of contaminated air; it permits a fairly uniform irradiation of the catalytic meshes and a good ratio of the irradiated surface area with respect to the volume of the gaseous reacting mixture. With these features, rather high TCE conversions can be obtained. © 2005 American Institute of Chemical Engineers AIChE J, 2005
Effect of ultrasound on the morphology and properties of polypropylene/inorganic filler composites
Authors: Chen Yingzi , Li Huilin
Published: May 2005

The effects of ultrasonic irradiation on the rheology, structure, and properties of PP/inorganic filler composites were studied. Scanning electron microscopy showed that ultrasound increased the orientation degrees of acicular fillers to the flow direction. WAXD indicated that ultrasound vibration induced sheet fillers orient with its surface perpendicular to the direction of the ultrasound vibration. The orderly rearrangements of fillers in the polymer melt induced by ultrasound vibration can reduce the steric hindrances in the flow field and increase the flowability of the PP/inorganic filler composites. The effect of ultrasound on reducing the apparent viscosities is very prominent, especially at lower shear rate. Ultrasound has an even more marked effect on reducing the apparent viscosities of composites containing fillers of larger size. With ultrasound vibration, the mechanical properties of the composites are also improved because of the orientation and uniform dispersion of fillers in the matrix. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1553–1560, 2005
Rheological behavior of semi‐aromatic transparent polyamide
Authors: Chen Jinzhou , Qu Liangjun , Li Xinfa , Jiang Aiyun , Niu Mingjun , Wang Jingwu
Published: May 2005

The rheological behaviors of semi‐aromatic transparent polyamide (SATPA) melt are investigated using a capillary rheometer. The effects of shear rate, shear stress, and temperature on the apparent viscosity ηa of SATPA are discussed. A correlation of non‐Newtonian index with temperature is obtained. The results show the shear thinning of SATPA; meanwhile ηa decreases with increasing temperature and shear rate, and the viscous flow activation energy is further obtained from temperature dependence of the samples. It was concluded that the apparent viscosity ηa is sensitive to temperature at lower shear rate owing to the higher viscous flow activation energy; on the contrary, the influence of temperature effect on the apparent viscosity becomes minor at higher shear rate due to the lower viscous flow activation energy. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1586–1589, 2005
Modification of an o‐cresol formaldehyde epoxy resin by the thermotropic liquid crystalline polymer
Authors: Huang Zeng Fang , Tan Song Ting , Wang Xia Yu
Published: May 2005

Two novel liquid crystalline polymers, polydiethyleneglycol bis(4‐hydroxybenzoate) terephthaloyl and block copolymer (PDBH), were synthesized by condensation reaction. The blends of the two liquid crystalline polymers and o‐cresol formaldehyde epoxy resin were prepared by linear phenol‐formaldehyde resin as curing reagent. Both mechanical and thermal properties of the blends containing liquid crystalline polymer were improved to a certain extent. By adding 5 wt % PDBH, the impact strength, bending strength, and the glass transition temperature were enhanced by 128%, 23.84%, and 28°C, respectively, compared with the unmodified version. The results of curing kinetics showed that the curing reaction active energy of the modified system by PDBH decreased from 79.70 to 70.26 kJ/mol. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1626–1631, 2005
Continuous polymerization of ω‐lauryl lactam in an intermeshing corotating twin‐screw extruder
Authors: Kim In , White James L.
Published: May 2005

This article describes the synthesis of poly(ω‐lauryl lactam) by a reactive extrusion process. Anionic ring‐opening polymerization was performed in an intermeshing corotating twin‐screw extruder. We investigated the evolution of conversion of ω‐lauryl lactam as a function of reaction time, screw speeds, different feed rates, and different screw configurations along the screw axis in a twin‐screw extruder. For comparison with continuous polymerization in a twin‐screw extruder, we studied polymerization in an internal mixer, which was considered a batch reactor. We found the final conversion of ω‐lauryl lactam made in a twin‐screw extruder was higher than in an internal mixer. Higher molecular weights are found at lower screw speeds and feed rates. Melt viscosities and mechanical properties of the polymers were measured. Residence time, molecular weights, and shear mixing have the main effect on the mechanical properties of products. The twin‐screw extruder performance was interpreted in terms of commercial software. It was found that twin‐screw extruder reaction rate was higher than those in the batch reactor and increased locally with screw speed and feed rate. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1605–1620, 2005
Isothermal and nonisothermal crystallization kinetics of novel even‐odd nylon 10 11
Authors: Cui Xiaowen , Yan Deyue , Wang Yanping
Published: May 2005

Isothermal and nonisothermal crystallization kinetics of even‐odd nylon 10 11 were investigated by differential scanning calorimetry (DSC). Equilibrium melting point was determined to be 195.20°C. Avarmi equation was adopted to describe isothermal and nonisothermal crystallization. A new relation suggested by Mo was used to analyze nonisothermal crystallization and gave a good result. The crystallization activation energies have been obtained to be −583.75 and −270.06 KJ/mol for isothermal and nonisothermal crystallization, respectively. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1637–1643, 2005
Statistical relationships between downloads and citations at the level of individual documents within a single journal
Authors: Moed Henk F.
Published: June 2005

Statistical relationships between downloads from ScienceDirect of documents in Elsevier's electronic journal Tetrahedron Letters and citations to these documents recorded in journals processed by the Institute for Scientific Information/Thomson Scientific for the Science Citation Index (SCI) are examined. A synchronous approach revealed that downloads and citations show different patterns of obsolescence of the used materials. The former can be adequately described by a model consisting of the sum of two negative exponential functions, representing an ephemeral and a residual factor, whereas the decline phase of the latter conforms to a simple exponential function with a decay constant statistically similar to that of the downloads residual factor. A diachronous approach showed that, as a cohort of documents grows older, its download distribution becomes more and more skewed, and more statistically similar to its citation distribution. A method is proposed to estimate the effect of citations upon downloads using obsolescence patterns. It was found that during the first 3 months after an article is cited, its number of downloads increased 25% compared to what one would expect this number to be if the article had not been cited. Moreover, more downloads of citing documents led to more downloads of the cited article through the citation. An analysis of 1,190 papers in the journal during a time interval of 2 years after publication date revealed that there is about one citation for every 100 downloads. A Spearman rank correlation coefficient of 0.22 was found between the number of times an article was downloaded and its citation rate recorded in the SCI. When initial downloads—defined as downloads made during the first 3 months after publication—were discarded, the correlation raised to 0.35. However, both outcomes measure the joint effect of downloads upon citation and that of citation upon downloads. Correlating initial downloads to later citation counts, the correlation coefficient drops to 0.11. Findings suggest that initial downloads and citations relate to distinct phases in the process of collecting and processing relevant scientific information that eventually leads to the publication of a journal article.
Chiral aspects of the human metabolism of ethosuximide
Authors: Millership J. S. , Mifsud J. , Galea D. , McRoberts W. C. , Hamilton J. T. G.
Published: June 2005

Ethosuximide is a chiral drug substance primarily indicated for the treatment of absence seizures. This drug is used clinically as the racemate. The human urinary metabolites of ethosuximide (I) have been studied using chiral gas chromatography (GC) and gas chromatography/mass spectrometry (GC/MS). The metabolites identified were the previously reported unchanged ethosuximide (I) enantiomers, all four stereoisomers of 2‐(1‐hydroxyethyl)‐2‐methylsuccinimide (II), and the four stereoisomers of 2‐ethyl‐3‐hydroxy‐2‐methylsuccinimide (III). Through chemical derivatization methodology and GC/MS (using electron impact ionization [EI] and chemical ionization [CI] techniques) two enantiomers of a previously unreported metabolite of ethosuximide, 2‐ethyl‐2‐hydroxymethylsuccinimide (VI), have been identified. Copyright © 2005 John Wiley & Sons, Ltd.
Local heating of human skin by millimeter waves: Effect of blood flow
Authors: Alekseev S.I. , Radzievsky A.A. , Szabo I. , Ziskin M.C.
Published: June 2005

We investigated the influence of blood perfusion on local heating of the forearm and middle finger skin following 42.25 GHz exposure with an open ended waveguide (WG) and with a YAV mm wave therapeutic device. Both sources had bell‐shaped distributions of the incident power density (IPD) with peak intensities of 208 and 55 mW/cm2, respectively. Blood perfusion was changed in two ways: by blood flow occlusion and by externally applied vasodilator (nonivamide/nicoboxil) cream to the skin. For thermal modeling, we used the bioheat transfer equation (BHTE) and the hybrid bioheat equation (HBHE) which combines the BHTE and the scalar effective thermal conductivity equation (ETCE). Under normal conditions with the 208 mW/cm2 exposure, the cutaneous temperature elevation (ΔT) in the finger (2.5 ± 0.3 °C) having higher blood flow was notably smaller than the cutaneous ΔT in the forearm (4.7 ± 0.4 °C). However, heating of the forearm and finger skin with blood flow occluded was the same, indicating that the thermal conductivity of tissue in the absence of blood flow at both locations was also the same. The BHTE accurately predicted local hyperthermia in the forearm only at low blood flow. The HBHE made accurate predictions at both low and high perfusion rates. The relationship between blood flow and the effective thermal conductivity (keff) was found to be linear. The heat dissipating effect of higher perfusion was mostly due to an apparent increase in keff. It was shown that mm wave exposure could result in steady state heating of tissue layers located much deeper than the penetration depth (0.56 mm). The surface ΔT and heat penetration into tissue increased with enlarging the irradiating beam area and with increasing exposure duration. Thus, mm waves at sufficient intensities could thermally affect thermo‐sensitive structures located in the skin and underlying tissue. Bioelectromagnetics 26:489–501, 2005. © 2005 Wiley‐Liss, Inc.
Numerical modeling and dosimetry of the 35 mm Petri dish under 46 GHz millimeter wave exposure
Authors: Zhao Jianxun , Wei Zhenggang
Published: June 2005

Experimental studies on effects of millimeter wave (MMW) exposure on cells cultured in Petri dishes have attracted interest in recent decades. To improve the quantification of the biological responses toward the MMW energy, an accurate and precise MMW dosimetry is to be provided. By using the finite difference time domain (FDTD) method, the numerical dosimetry is performed for a typical 35 mm Petri dish under 46 GHz continuous MMW exposure from an irradiator of a specified power pattern. With the aim of building a precise model, the meniscus at the interface between the culture solution and the Petri dish sidewall is taken into account, followed by the modeling of smooth edges of the Petri dish. The trilinear interpolation is introduced to assist the FDTD method to obtain a more precise dosimetric assessment. The specific absorption rate (SAR) distributions in the cornea cells covered by culture solution in the Petri dish are calculated and compared to display the effects of using Petri dish models of various precision and the trilinear interpolation on dosimetry results. In addition, the SAR distribution in the cells is analyzed to study its homogeneity. The results indicate that the precise Petri dish model and the application of the trilinear interpolation are helpful in improving the precision of numerical dosimetry. It is also revealed that the inhomogeneity of the SAR distribution is well beyond neglect, which deserves cautious consideration in experiments investigating MMW effects on cells invitro. Bioelectromagnetics 26:481–488, 2005. © 2005 Wiley‐Liss, Inc.
Skin temperature increase caused by a mobile phone: A methodological infrared camera study
Authors: Straume Aksel , Oftedal Gunnhild , Johnsson Anders
Published: June 2005

Mobile phone users often complain about burning sensations or a heating of the ear region. The increase in temperature may be due to thermal insulation by the phone, heating of the mobile phone resulting from its electrical power dissipation, and radio frequency (RF) exposure. The main objective of this study was to use infrared (IR) camera techniques to find how much each of these factors contributes to the increase in skin temperature resulting from the use of one GSM 900 phone. One subject, a healthy male took part in the study. He was holding the phone in a normal position when the phone was switched off, when it was switched on but with the antenna replaced by a 50 Ω load to eliminate the RF exposure, and when it was transmitting RF fields. The output power could be fixed, and the minimal and the maximal power levels of the phone were used. The study was designed as a double blind experiment. The changes in temperature after 15 and 30 min of mobile phone use were calculated on the exposed side of the head relative to the unexposed side. The insulation and the electrical power dissipation lead to statistically significant rises in the skin temperature, while the RF exposure did not. Bioelectromagnetics 26:510–519, 2005. © 2005 Wiley‐Liss, Inc.