Substances known to alter cyclic nucleotide levels in cells were applied to the isolated toad retina and effects on rod electrical and adaptive behavior were studied. The retina was continually superfused in control ringer’s or ringer’s containing one or a combination of drugs, and rod activity was recorded intracellularly. Superfusion with cGMP, Bu(2)GMP, isobutylmethylxanthine (IBMX; a phosphodiesterase inhibitor), or PGF(2α) (a prostaglandin) caused effects in rods that closely match those observed when extracellular Ca(2+) levels were lowered. For example, short exposures (up to 6 min) of the retina to these substances caused depolarization of the membrane potential, increase in response amplitudes, and some changes in waveform; but under dark-adapted or partially light-adapted conditions receptor sensitivity was virtually unaffected. That is, the position of the V-log I curve on the intensity axis was determined by the prevailing light level, not by drug level. These drugs, like lowered extracellular Ca(2+), also decreased the period of receptor saturation after a bright-adapting flash, resulting in an acceleration of the onset of membrane and sensitivity recovery during dark adaptation.
Long-term (6-15 min) exposure of a dark-adapted retina to 5 mM IBMX or a combination of IBMX and cGMP caused a loss of response amplitude and a desensitization of the rods that was similar to that observed in rods after a long-term low Ca(2+) (10(-9)M) treatment. Application of high (3.2 mM) Ca(2+) to the retina blocked the effects of applied Bu(2)cGMP. PGE(1) superfusion mimicked the effects of increasing extracellular Ca(2+). The results show that increased cGMP and lowered Ca(2+) produce similar alterations in the electrical activity of rods. These findings suggest that Ca(2+) and cGMP are interrelated messengers. We speculate that low Ca(2+) may lead to increased intracellular cGMP, and/or that applied cGMP, and/or that applied cGMP may lower cytosol Ca(2+), perhaps by stimulating Ca(2+)- ATPase pumps in the outer segment.
Functional studies of the methuselah/methuselah-like (mth/mthl) gene family have focused on the founding member mth, but little is known regarding the developmental functions of this receptor or any of its paralogs. We undertook a comprehensive analysis of developmental expression and sequence divergence in the mth/mthl gene family. Using in situ hybridization techniques, we detect expression of six genes (mthl1, 5, 9, 11, 13, and 14) in the embryo during gastrulation and development of the gut, heart, and lymph glands. Four receptors (mthl3, 4, 6, and 8) are expressed in the larval central nervous system, imaginal discs, or both, and two receptors (mthl10 and mth) are expressed in both embryos and larvae. Phylogenetic analysis of all mth/mthl genes in five Drosophila species, mosquito and flour beetle structured the mth/mthl family into several subclades. mthl1, 5, and 14 are present in most species, each forming a separate clade. A newly identified Drosophila mthl gene (CG31720; herein mthl15) formed another ancient clade. The remaining Drosophila receptors, including mth, are members of a large "superclade" that diversified relatively recently during dipteran evolution, in many cases within the melanogaster subgroup. Comparing the expression patterns of the mth/mthl "superclade" paralogs to the embryonic expression of the singleton ortholog in Tribolium suggests both subfunctionalization and acquisition of novel functionalities. Taken together, our findings shed novel light on mth as a young member of an adaptively evolving developmental gene family. 相似文献
We report the isolation and some properties of a flavodoxin from a eukaryotic organism, the naturally occurring red alga . Unlike the situation with most other organisms the flavodoxin, under normal growth conditions, is the predominantly formed low-potential electron carrier, an accompanying ferredoxin occurring in only very small amounts. The flavodoxin is of molecular weight 21000 and one mole of FMN is present per mole of protein. Reduction of the flavoprotein proceeds via a blue flavosemiquinone radical. The flavodoxin is active both in photosynthetic NADP reduction by broken chloroplasts, and in phosphoroclastic cleavage of pyruvate by cell-free extracts of . 相似文献
Inhibition of quorum sensing (QS)-regulated virulence factors including biofilm is a recognized anti-pathogenic drug target. The search for safe and effective anti-QS agents is expected to be useful to combat diseases caused by multidrug-resistant bacteria. In this study, effect of a commonly used antibiotic, doxycycline on QS was evaluated using sensor strains of Chromobacterium violaceum (ATCC 12472 and CVO26) and Pseudomonas aeruginosa PAO1. Sub-MICs of doxycycline reduced QS-controlled violacein production in C. violaceum to a significant degree (70 %) and showed a significant reduction of LasB elastase (67.2 %), pyocyanin (69.1 %), chitinase (69.8 %) and protease (65 %) production and swarming motility (74 %) in P. aeruginosa PAO1 over untreated controls. Similar results were also recorded against a clinical strain of P. aeruginosa (PAF-79). Interestingly, doxycycline at respective sub-MICs (4 and 32 μg ml?1) significantly reduced the biofilm-forming capability and exopolysaccharide production in both the strains of P. aeruginosa (PAO1 and PAF-79) over untreated controls. The results of this study highlight the multiple actions of doxycycline against QS-linked traits/virulence factors and its potential to attenuate virulence of P. aeruginosa. 相似文献
Genetic analysis of Bacteroides fragilis (BF) is hindered because of the lack of efficient transposon mutagenesis methods. Here, we describe a simple method for transposon mutagenesis using EZ::TN5, a commercially available system that we optimized for use in BF638R. The modified EZ::TN5 transposon contains an Escherichia coli conditional origin of replication, a kanamycin resistance gene for E. coli, an erythromycin resistance gene for BF , and 19 basepair transposase recognition sequences on either ends. Electroporation of the transposome (transposon-transposase complex) into BF638R yielded 3.2 ± 0.35 × 10(3) CFU μg(-1) of transposon DNA. Modification of the transposon by the BF638R restriction/modification system increased transposition efficiency sixfold. Electroporation of the EZ::TN5 transposome results in a single-copy insertion of the transposon evenly distributed across the genome of BF638R and can be used to construct a BF638R transposon library. The transposon was also effective in mutating a BF clinical isolate and a strain of the related species, Bacteroides thetaiotaomicron. The EZ::TN5-based mutagenesis described here is more efficient than other transposon mutagenesis approaches previously reported for BF. 相似文献
A series of Au, Ru, and Cu complexes of metronidazole (= [1-(2-hydroxyethyl)-2-methyl-5-nitro-1H-imidazole; 1) were prepared as highly potent anti-amoebic drugs. The complexes [Au(PPh3)(1)]PF6 (2), [Ru(1)2(Cl)2(H2O)2] (3), and [Cu(1)2(mu-Cl)(H2O)]2Cl2 (4) were readily synthesized from [Au(PPh3)Cl], RuCl3 x 3 H2O, and CuCl2 x 2 H2O, respectively. All complexes were thoroughly characterized by IR, UV/VIS, 1H-NMR, FAB-MS, elemental and thermogravimetric analyses, and, in the case of 4, also by X-ray crystallography (Fig. 1). All complexes were evaluated in vitro as growth inhibitors of Entamoeba histolytica (HM1:IMSS strain). Their IC50 values were in the range of 0.10-0.51 microM (Table 2), which makes these drugs, especially the Cu(II) complex 4, considerably more potent than uncomplexed metronidazole (1; IC50 = 1.81 microM), the current standard drug for the worldwide treatment of amoebiasis. 相似文献
It is known that phosphorus deficiency results in alterationsin the assimilation of nitrogen. An experiment was conductedto investigate mechanisms involved in altered 15NO3 uptake,endogenous 15N translocation, and amino acid accumulation insoybean (Glycine max L. Merrill, cv. Ransom) plants deprivedof an external phosphorus supply for 20 d in solution culture.Phosphorus deprivation led to decreased rates of 15NO3uptake and increased accumulation of absorbed 15N in the root.Both effects became more pronounced with time. Asparagine, theprimary transport amino acid in soybean, accumulated in largeexcess in roots and stems. In roots of phosphorus-deprived plants,concentrations of ATP and inorganic phosphate declined rapidly,but dry weight accumulation was similar to or above that ofthe control even after 20 d of treatment. Arginine accumulationin leaves was greatly enhanced, even though 15N partitioninginto the insoluble reduced-N fraction of leaves was unaffected.The results suggest that decreases in NO3 uptake in lowphosphorus plants could be caused by feedback control factorsand by limited ATP availability. The decline in endogenous Ntransport from the root to the shoot may be associated withchanges in membrane properties, which also result in paralleleffects on hydraulic conductance and the upward flow of waterthrough the plant. Key words: Phosphorus stress, nitrate uptake, nitrate translocation, arginine 相似文献