Purification and characterization of 2'aminobiphenyl-2,3-diol 1,2-dioxygenase from Pseudomonas sp. LD2

Carbazole is a nitrogen-containing heteroaromatic compound that occurs as a widespread and mutagenic environmental pollutant. The 2'aminobiphenyl-2,3-diol 1,2-dioxygenase involved in carbazole degradation was purified to near electrophoretic homogeneity from Pseudomonas sp. LD2 by a combination of ion-exchange chromatography, ammonium sulfate precipitation, and hydrophobic interaction chromatography. This purification was challenging due to the great instability of the enzyme under many standard conditions. The enzyme was also purified to electrophoretic homogeneity from recombinant Escherichia coli expressing the 2'aminobiphenyl-2,3-diol 1,2-dioxygenase-encoding gene cloned from Pseudomonas sp. LD2. The molecular mass of the native enzyme was determined by gel filtration to be 70 kDa. The subunit molecular masses were determined to be 25 and 8 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, indicating that the dioxygenase is an [alpha2beta2] heterotetramer. The optimal temperature and pH for the enzymatic production of 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid (HOPDA) from 2,3-dihydroxybiphenyl were determined to be 40 degrees C and 8.0, respectively. The maximum observed specific activity on 2,3-dihydroxybiphenyl was 48.1 mmol HOPDA min(-1) mg(-1). This indicated a maximum observed turnover rate of 360,000 molecules HOPDA enz(-1) s(-1). The K'm inhibition constant Ks and Vmax on 2,3 dihydroxybiphenyl were determined to be 5 microM, 37 microM, and 44 mmol min(-1) mg(-1), respectively. These results show that 2'aminobiphenyl-2,3-diol 1,2-dioxygenase is a meta-cleavage enzyme related to the 4,5-protocatechuate dioxygenase family, with comparable purification challenges posed by intrinsic enzyme instability.     

Effects of hypotonic shock on intracellular pH in bovine articular chondrocytes

Chondrocytes inhabit an unusual environment, in which they are repeatedly subjected to osmotic challenges as fluid is expressed from the extracellular matrix during static joint loading. In the present study, the effects of hypotonic shock on intracellular pH, pH(i), have been studied in isolated bovine articular chondrocytes using the pH-sensitive fluroprobe BCECF. Cells subjected to a 50% dilution rapidly alkalinised, by approximately 0.2 pH units, a sustained plateau being achieved within 300 s. The effect was not altered by inhibitors of pH regulators, such as amiloride, bafilomycin and SITS, but was absent when cells were subjected to hypotonic shocks in solutions in which Na(+) ions were replaced by NMDG(+). The response was found to be sensitive to Gd(3+) ions, blockers of stretch-activated cation channels. Alkalinisation was also inhibited by treatment with Zn(2+) ions, at a concentration reported to block voltage-activated H(+) channels (VAHC). Depolarisation using high K(+) solutions supplemented with valinomycin also induced intracellular alkalinisation. Measurements using a membrane potential (E(m)) fluorescent dye showed that E(m) was approximately -44 mV, but was depolarised by over 50 mV following HTS. The depolarisation was also inhibited by Na(+) substitution with NMDG(+) or treatment with Gd(3+). We conclude that in response to HTS the opening of a stretch-activated cation channel leads to Na(+) influx, which results in a membrane depolarisation. Subsequent activation of VAHC permits H(+) ion efflux along the prevailing electrochemcial gradient, leading to the alkalinisation, which we record.     

Dietary dehydroepiandrosterone inhibits bone marrow and leukemia cell transplants: role of food restriction

Dietary dehydroepiandrosterone (DHEA) inhibits the proliferation of syngeneic bone marrow cells (BMC) infused into lethally irradiated mice. Potential mechanisms for suppression of hematopoiesis were evaluated and the findings were as follows: (i) depletion of NK, T, B or macrophage cells failed to reverse suppression by DHEA; (ii) stem cell stimulation by erythropoietin, growth hormone, interleukin-2, Friend leukemia virus, or cyclophosphamide failed to reverse suppression; (iii) supplementation of fatty acids, mevalonate, or deoxyribonucleotides, which are dependent upon glucose-6-phosphate dehydrogenase function, did not enhance BMC growth in mice fed DHEA; (iv) DHEA downstream metabolites 4-androstenedione and 17beta-estradiol, as well as the synthetic steroid, 16alpha-chloroepiandrosterone (but not testosterone or 5-androstene-3beta,17beta-diol), also inhibited BMC growth. Tamoxifen antagonized the effects of 17beta-estradiol but not DHEA; (v) dietary DHEA causes hypothermia, but housing of DHEA-fed mice at 34 degrees C to maintain normal body temperature did not reverse suppression; (vi) DHEA leads to a decrease in food intake in rodents. Pair-feeding control diet to mice fed DHEA mimicked the effects of dietary DHEA; (vii) adrenalectomy and orchiectomy decrease the levels of stress and sex hormones, respectively. Neither procedure affected the ability of food restriction or DHEA feeding to inhibit hematopoiesis; (viii) growth of GR-3 NM pre-B leukemia cells in unirradiated mice was also suppressed by DHEA or food restriction. We conclude that DHEA, by reducing food intake in mice, inhibits bone marrow and leukemia cell growth. The precise mechanism(s) by which reduced food intake per se inhibits hematopoiesis is not known, but may involve an increased rate of cellular apoptosis.     

Role of gap junctions in fluid secretion of lacrimal glands

In glands such as the liver and pancreas, gap junctions containing connexin 26 and 32 (Cx26 and Cx32, respectively) couple the secretory cells. Uncoupling these junctions compromises the secretory function of these glands. Lacrimal glands also contain extensive arrays of gap junctions consisting of Cx26 and Cx32. We wanted to determine the role of these junctions in fluid secretion. In Cx32-deficient mice, immunocytochemistry showed that, in the male lacrimal gland, the remaining Cx26 was found evenly distributed in the membrane whereas there was little in the membranes of female glands. Western blot analysis of Cx26 showed that female Cx32-deficient mice expressed Cx26. Patch-clamp analyses of acinar cell coupling showed that the cell pairs from male glands were coupled whereas those from female glands were not. Stimulated fluid production by the glands from Cx32-deficient mice was abnormally low in female glands compared with controls at low topical doses of carbachol. The protein secretory response to different doses of carbachol was the same in all animals. These data suggest that gap junctions are essential for optimal fluid secretion in lacrimal glands.     

The connecting segment between both epidermal growth factor-like domains in blood coagulation factor IX contributes to stimulation by factor VIIIa and its isolated A2 domain

The light chain of activated factor IX comprises multiple interactions between both epidermal growth factor-like domains that contribute to enzymatic activity and binding of factor IXa to its cofactor factor VIIIa. To investigate the association between factor IXa-specific properties and surface-exposed structure elements, chimeras were constructed in which the interconnection between the modules Leu(84)-Thr(87) and the factor IX-specific loop Asn(89)-Lys(91) were exchanged for corresponding regions of factor X and factor VII. In absence of factor VIIIa, all chimeras displayed normal enzymatic activity. In the presence of factor VIIIa, replacement of loop Asn(89)-Lys(91) resulted in a minor reduction in factor IXa activity. However, chimeras with substitutions or insertions in the spacer between the epidermal growth factor-like domains showed a major defect in response to factor VIIIa. Of these chimeras, some displayed a normal response to isolated factor VIII A2 domain as a cofactor in factor X activation. Surprisingly, chimeras containing elongated inter-domain spacers from factor X or VII displayed reduced response to both complete factor VIIIa and the isolated A2 domain. Moreover, these chimeras still displayed effective association with immobilized A2 domain as assessed by surface plasmon resonance. We conclude that both sequence and length of the junction Leu(84)-Thr(87) between both epidermal growth factor-like domains contribute to the enhancement of factor IXa enzymatic activity that occurs upon assembly with factor VIIIa.     

Imaging technique implemented in CellTracks system

BACKGROUND: We developed the CellTracks cell analysis system that, similar to flow cytometry, yields multiparameter information by which the cells can be differentiated. We describe the implementation of a laser scanning imaging method in the system. Image analysis of the cells improves the specificity of cell classification, especially in cases where the particular cells are found relatively infrequently and one has to discriminate between artifacts and real events. METHODS: Fluorescent images of immunomagnetically labeled and aligned cells are obtained by passing the cells through a laser focus. The laser focus is smaller than the objects and subsequent frames captured by a regular surveillance CCD camera with a frame grabber board represent different parts of the cells. Complete images of the cells are constructed by shifting each image with respect to each other and adding individual pixel values. RESULTS: The power of combining a fluorescent image with multiparametric data is demonstrated by imaging fluorescent and magnetically labeled beads and cells. The image gives additional information about the dye distribution across the objects. Changes in dye distribution as a function of time were observed in leukocytes labeled with the red fluorescent label, Oxazine750, which are imaged at different time intervals. CONCLUSIONS: An imaging technique implemented in the CellTracks system provides high-resolution fluorescent images of events previously identified by the system. The images of the fluorescent cells enhance the ability to classify rare events.     

Human marrow-derived mesenchymal progenitor cells

A number of adult mesenchymal tissues contain subpopulations of undifferentiated cells, which retain the capacity to differentiate along multiple lineages. These mesenchymal progenitor cells may be cultured in an undifferentiated state and, when given the appropriate signals, differentiate into an expanding list of several mesenchymal and a few ectodermal derived tissues. The maintenance and propagation of the multipotential nature of these progenitor cell populations are crucially dependent on the isolation protocol, the culture expansion conditions, particularly the properties of the fetal bovine serum supplement in the culture medium. This article describes a method for selection of the appropriate serum lot, and introduces a simplified isolation technique to optimize the yield of progenitor cells that maintain the capability of undergoing multilineage differentiation in response to appropriate cues. Cell populations isolated and culture expanded in this manner, by virtue of their multiple differentiation potential, should serve as ideal candidate cells for tissue engineering applications for the repair and regeneration of tissue damaged by disease and or trauma.     

New 3-deoxyanthocyanidins from leaves of Arrabidaea chica

Two new 3-deoxyanthocyanidins, 6,7,3',4'-tetrahydroxy-5-methoxyflavylium and 6,7,4'-trihydroxy-5-methoxyflavylium, and the pigment carajurin, which has been previously identified, were isolated from dried leaves of Arrabidaea chica, a creeper native to the American tropics. The structures of the components were elucidated by 1H- and 13C-NMR spectroscopy and HPLC-MS, including X-ray crystallographic analysis for carajurin.     

The expression and regulation of the iron transport molecules hephaestin and IREG1: implications for the control of iron export from the small intestine

The amount of iron in the body is controlled at the point of absorption in the proximal small intestine. Dietary iron enters the intestinal epithelium via the brush-border transporter DMT1 and exits through the basolateral membranes. The basolateral transfer of iron requires two components: a copper-containing iron oxidase known as hephaestin and a membrane transport protein IREG1. The amount of iron traversing the enterocytes is directly related to body iron requirements and inversely related to the iron content of the intestinal epithelium. We propose that body signals control iron absorption by first acting on crypt enterocytes to determine the expression of basolateral transport components. This, in turn, modulates the intracellular iron content of mature epithelial cells, which ultimately determines the activity of the brush-border transporter DMT1.