CaATP inhibition of the MgATP-dependent proton pump (H+-ATPase) in bacterial photosynthetic membranes with a mechanism of alternative substrate inhibition

 The membrane-bound F1 sector of the H⁺–ATPase complex (F-type ATPase) in dark-adapted photosynthetic chromatophores is endowed with MgATP- and CaATP-dependent ATPase activities, both sensitive to inhibitors such as oligomycin and venturicidin. Because of contatamination of free Mg^{2 +} and Ca²⁺ ions in chromatophore preparations, kinetic characterization of the two hydrolitic reactions can be performed only in the presence of both substrates, using a model for two alternative substrates. The two activities are characterized by similar maximal rates and affinity constants [V_MgATP and V_CaATP: 13±1 and 10±1 nmol s^–1 ATP hydrolyzed (μmol BChl)^–1; K_MgATP and K_CaATP: 0.22±0.06 and 0.20±0.05 mm]. However, only the MgATP-dependent ATPase is coupled to Δ*_{H +} generation. In this process CaATP acts as an alternative substrate and a competitive inhibitor of the proton pump, with a K_I coincident with K_CaATP for the hydrolytic activity. This finding highlights the central role that the coordination chemistry of the ion-nucleotide complex plays in determining the proton gating mechanism at the catalytic site(s) of the enzyme complex. These results are discussed on the basis of the coordination properties of the ions and of the available information on the protein structure. Received: 5 December 1995 / Accepted: 7 March 1996     

Oligosaccharides derived from the xyloglucan isolated from the seeds of Hymenaea courbaril var. stilbocarpa

On aqueous extraction, Hymenaea courbaril var. stilbocarpa, known in Brazil as jatobá, furnishes a high yield of viscous xyloglucan (45%) from its seeds. The crude polysaccharide (B1) was hydrolysed and the products, analysed as alditol acetates, were glucose, xylose, galactose and arabinose in the ratio 50:35:13:2. After further fractionation on a DEAE-cellulose column (chloride form), the main fraction (70% yield, B2) was obtained. The basic structure of the xyloglucan was determined as a cellulose-type (1 → 4)-linked β-d-glucan backbone partially substituted with side chains at 06 of -d-xylopyranose, some of which were themselves substituted at 02 by the units of β-d-galactopyranose. Treatment of the xyloglucan (B2) with commercial cellulase from Trichoderma sp. yielded six oligosaccharides. These oligosaccharides were isolated by preparative paper chromatography, and their structures were determined by gas-liquid chromatography-mass spectroscopy of the derived partially O-methylated alditol acetates. These results confirm the structure proposed for jatobá seed xyloglucan.     

Polysaccharides from the seeds of Senna multijuga

The seeds of Senna multijuga were extracted with water or 1% acetic acid and treated with ethanol, resulting in two insoluble fractions. After purification, the major one (FIA, 23%) was shown to be a galactomannan (Man:Gal 2.3:1;[] = + 54.6;[η]=1340mlg⁻¹). It consists of a main chain of (1 → 4)-linked β-d-mannopyranosyl residues substituted at 06 by single-unit -d-galactopyranosyl side chains. The second fraction (FIB, 2.5%) was an O-acetyl-glucuronoarabinoxylan from the seed coats (O-acetyl 8.3 mol%; glucuronic acid 11.7%, Xyl:Ara ratio 20:1), which showed a predominance of 4-O-substituted Xylp units (84.4%), branched at 03 with non-reducing end units of Xylp, Araf and glucuronic acid. The O-acetyl positions in d-xylosyl units are at 02 (4.8%), 03 (4.4%) and 02,3 (0.9%). The ratio between 03 and 02 determined by ¹³C-nuclear magnetic resonance spectroscopy is 1.5:1.     

Precise physical mapping of theEscherichia coli rnb gene, encoding ribonuclease II

Ribonuclease II (encoded byrnb) is one of the two main exonucleases involved in mRNA degradation inEscherichia coli. We report the precise physical mapping ofrnb to 29 min on the chromosomal map in the vicinity ofpyrF, and clarify the genetic and physical maps of thisE. coli chromosomal region. The results were confirmed by the construction of a strain partially deleted forrnb.     

Phenotypic features of breast cancer cells overexpressing ornithine-decarboxylase

Polyamines (PA) have been shown to be critical mediators of estradiol-induced breast cancer cell proliferation. This finding suggests that constitutive activation of the PA pathway may promote tumor progression, possibly leading to hormone independence. To test this hypothesis, we transfected hormone-responsive MCF-7 breast cancer cells with a complementary DNA coding for ornithine-decarboxylase (ODC), the first rate-limiting enzyme in PA biosynthesis. Marked ODC over-expression observed in stably transfected clones was associated with a selective increase in cellular putrescine content, while spermidine and spermine levels were not altered. ODC-overexpressing MCF-7 cells were resistant to the antiproliferative effects of low but not high concentrations of the enzyme inhibitor, α-difluoromethylornithine. In agreement with our hypothesis, sensitivity to the growth-promoting action of estradiol was reduced by approximately one third (P < 0.001) in ODC-overexpressing MCF-7 cells compared with vector-only transfected clones. Basal growth under anchorage-dependent conditions was only marginally increased by ODC overexpression (P = 0.048), while clonogenicity in soft agar was actually reduced. These data suggest that activation of PA biosynthesis may contribute in part to the acquisition of estrogen independence by breast cancer cells. Since only putrescine content was increased as a result of ODC overexpression, these data may underestimate the overall influence of the PA pathway on breast cancer phenotype. © 1995 Wiley-Liss, Inc.     

Functional characterization of lymphoid cells generated in serum-deprived culture stimulated with stem cell factor and interleukin 7 from normal and autoimmune mice

We have investigated the phenotypic and functional characteristics of murine pre-B cells obtained in semisolid and liquid culture with stem cell factor (SCF) and interleukin 7 (IL-7). Both serum-supplemented and serum-deprived culture conditions were used. The source of bone marrow cells was either normal mice (CD1 and C3H) or the lupus strain of mice MRL/Ipr and its congenic strain MRL/+. SCF (100 ng/ml) and IL-7 (250 ng/ml) supported murine B cell proliferation in vitro from all the murine strains analyzed both in serum-supplemented and serum-deprived conditions. Maximal colony growth was observed in both cases when the factors were used in combination. The growth factors alone induced some colony growth in serum-supplemented cultures but were either ineffective or had modest activity in serum-deprived cultures. Cells harvested from the colonies or generated in liquid cultures and stimulated with SCF + IL-7 in the absence of serum had almost exclusively a pre-B cell phenotype (BP-1+, B220+, slg-, CD4-, CD8-, Mac-1, RB-6-). Both the maximal colony growth in semisolid culture and the maximal number of cells in liquid culture were observed at day 12–14. At this time, the pre-B cells failed to differentiate further and started to die. Pre-B cells generated in vitro were, however, capable of differentiating in vivo. SCID mice injected with 2 × 10⁶ pre-B cells had readily detectable serum levels of IgM (54 ± 26 m?g/ml) and IgG (60 ± 95 m?g/ml) at 4 weeks and 6 weeks posttransplantation, respectively. Mature B and T cells of the donor major histocompatibility complex type were detected in the SCID mice at sacrifice 14 weeks posttransplantation. These data indicate that purified (>80% BP-1+) populations of functional pre-B cells can be grown from murine bone marrow of normal mice as well as of lupus mice in serum-deprived cultures stimulated with SCF and IL-7. These cultures, therefore, provide a highly enriched source of pre-B cells but also contain T cell precursors that differentiate upon adoptive transfer into SCID mice. © 1995 Wiley-Liss, Inc.     

Specific induction of self-discrimination by follicle cells in Ciona intestinalis oocytes

Self-incompatibility, a mechanism that prevents self-fertilization in ascidians, is based on the ability of the oocyte vitelline coat to distinguish and accept only heterologous spermatozoa. In Ciona intestinalis self-discrimination is established during late oogenesis and is contributed or controlled by products of the overlying follicle cells. In this study we have further investigated the role of the follicle cells in the onset of self-discrimination by using in vitro maturation of ovarian oocytes deprived of the follicle cells and incubated with either autologous or heterologous follicle cells. Fertilization assays demonstrate that the action of the follicle cells is exerted even when they are detached from the vitelline coat and that only autologous follicle cells can promote the induction of self-sterility on the egg coat. Electron microscopy of the oocytes during maturation reveals that the switch from self-fertility to self-sterility is accompanied by the appearance of a thin electron-dense layer on the outer surface of the vitelline coat. We suggest that the formation of this layer is the result of the interaction between products of the follicle cells and the autologous vitelline coat.     

Long-Term Induction of Tyrosine Hydroxylase Expression: Compensatory Response to Partial Degeneration of the Dopaminergic Nigrostriatal System in the Rat Brain

Abstract: The present study was undertaken to examine the adaptive changes occurring 1 and 6 months after moderate or severe unilateral 6-hydroxydopamine-induced lesions confined to the lateral part of the rat substantia nigra pars compacta (SNC). The expression of tyrosine hydroxylase (TH) enzyme was analyzed in the remaining dopaminergic nigral cell bodies and in the corresponding striatal nerve endings. In the cell bodies of the lesioned SNC, TH mRNA content was increased (+20 to +30%) 6 months after the lesion without changes in cellular TH protein amounts. The depletion of TH protein in the nerve terminal area was less severe than the percentage of cell loss observed in the SNC at 1- and 6-month postlesion intervals. Moreover, the decrease in TH protein in the ipsilateral striatum was less pronounced 6 months after lesion than 1 month after. That no corresponding change in TH protein content was observed in the cell bodies at a time when TH increased in nerve terminals suggests that the newly synthesized protein is probably rapidly transported to the striatal fibers. These results suggest the existence of a sequence of changes in TH expression between cell bodies and fibers, occurring spontaneously after partial denervation of the nigrostriatal pathway.     

The effect of aluminum on cytokinins in the mycelia of Amanita muscaria

High performance liquid chromatography analysis of immunoaffinity-purified extracts of mycelia of Amanita muscaria, and the Amaranthus bioassay of the eluted fractions, revealed the following seven cytokinins: zeatin, zeatin riboside, zeatin N-9-glucoside, dihydrozeatin, dihydrozeatin riboside, isopentenyl adenine, and isopentenyl adenosine. The decreased growth of aluminum-treated mycelia correlated with a 35% decrease in the total amount of the cytokinins. Among individual cytokinins, zeatin was the most affected, exhibiting a reduction of about 90%. The results are compared with previous investigations of aluminum effects on cytokinins in the mycelia of Lactarius piperatus, whose growth is stimulated by aluminum.Abbreviations ZR zeatin riboside - iPA isopentenyl adenosine - Z zeatin - DHZ dihydrozeatin - iP isopentenyl adenine - DHZR dihydrozeatin riboside - Z-9G zeatin N-9-glucoside - iP-9G isopentenyl N-9-glucoside - HPLC high performance liquid chromatography - DHZRMP dihydrozeatin riboside monophosphate - ZRMP zeatin riboside monophosphate