bluuebunny/crossref_metadata_2025_split huggingface dataset:
Apparent Absence of a Redox Requirement for Blue Light Activation of Pump Current in Broad Bean Guard Cells
Authors: Taylor Alison R. , Assmann Sarah M. 
Published: July 2002

Abstract
In guard cells, membrane hyperpolarization in response to a blue light (BL) stimulus is achieved by the activation of a plasma membrane H+-ATPase. Using the patch clamp technique on broad bean (Vicia faba) guard cells we demonstrate that both steady-state- and BL-induced pump currents require ATP and are blocked by vanadate perfused into the guard cell during patch clamp recording. Background-pump current and BL-activated currents are voltage independent over a wide range of membrane potentials. During BL-activated responses significant hyperpolarization is achieved that is sufficient to promote K+ uptake. BL activation of pump current becomes desensitized by three or four pulses of 30 s × 100 μmol m−2 s−1 BL. This desensitization is not a result of pump inhibition as maximal responses to fusicoccin are observed after full BL desensitization. BL treatments prior to whole cell recording show that BL desensitization is not due to washout of a secondary messenger by whole cell perfusion, but appears to be an important feature of the BL-stimulated pump response. We found no evidence for an electrogenic BL-stimulated redox chain in the plasma membrane of guard cells as no steady-state- or BL-activated currents are detected with NADH or NADPH added to the cytosol in the absence of ATP. Steady-state- nor BL-activated currents are affected by the inclusion along with ATP of 1 mm NADH in the pipette under saturating red light or by including NADPH in the pipette under darkness or saturating red light. These data suggest that reduced products of photosynthesis do not significantly modulate plasma membrane pump currents and are unlikely to be critical regulators in BL-stimulation of the plasma membrane H+-ATPase in guard cells.
The Light Sensitivity of ATP Synthase Mutants ofChlamydomonas reinhardtii
Authors: Majeran Wojciech , Olive Jacqueline , Drapier Dominique , Vallon Olivier , Wollman Francis-André 
Published: July 2002

AbstractChlamydomonas reinhardtii mutants defective in the chloroplast ATP synthase are highly sensitive to light. The ac46 mutant is affected in the MDH1 gene, required for production or stability of the monocistronic atpH mRNA encoding CFO-III. In this and other ATP synthase mutants, we show that short-term exposure to moderate light intensities—a few minutes—induces an inhibition of electron transfer after the primary quinone acceptor of photosystem II (PSII), whereas longer exposure—several hours—leads to a progressive loss of PSII cores. An extensive swelling of thylakoids accompanies the initial inhibition of electron flow. Thylakoids deflate as PSII cores are lost. The slow process of PSII degradation involves the participation of ClpP, a chloroplast-encoded peptidase that is part of a major stromal protease Clp. In the light of the above findings, we discuss the photosensitivity of ATP synthase mutants with respect to the regular photoinhibition process that affects photosynthetic competent strains at much higher light intensities.
The Enhancement of Phototropin-Induced Phototropic Curvature in Arabidopsis Occurs via a Photoreversible Phytochrome A-Dependent Modulation of Auxin Responsiveness
Authors: Stowe-Evans Emily L. , Luesse Darron R. , Liscum Emmanuel 
Published: July 2002

AbstractThe induction of phototropism in etiolated (dark-grown) seedlings exposed to an unidirectional pulse or extended irradiation with low fluence rate blue light (BL) requires the action of the phototropin (nph1) BL receptor. Although cryptochromes and phytochromes are not required for phototropic induction, these photoreceptors do modulate the magnitude of curvature resulting from phototropin activation. Modulatory increases in the magnitude of phototropic curvature have been termed “enhancement.” Here, we show that phototropic enhancement is primarily a phytochrome A (phyA)-dependent red/far-red-reversible low fluence response. This phyA-dependent response is genetically separable from the basal phototropin-dependent response, as demonstrated by its retention under extended irradiation conditions in the nph4 mutant background, which normally lacks the basal BL-induced response. It is interesting that thenph4 mutants fail to exhibit the basal phototropin-dependent and phyA-dependent enhancement responses under limiting light conditions. Given that NPH4 encodes a transcriptional activator, auxin response factor 7 (ARF7), we hypothesize that the ultimate target(s) of phyA action during the phototropic enhancement response is a rate-limiting ARF-containing transcriptional complex in which the constituent ARFs can vary in identity or activity depending upon the irradiation condition.
Cell Cycle Regulation of Cyclin-Dependent Kinases in Tobacco Cultivar Bright Yellow-2 Cells
Authors: Sorrell David A. , Menges Margit , Healy J.M. Sandra , Deveaux Yves , Amano Chinatsu , Su Ya , Nakagami Hirofumi , Shinmyo Atsuhiko , Doonan John H. , Sekine Masami , Murray James A.H. 
Published: July 2002

Abstract
Plants possess two major classes of cyclin-dependent kinases (CDK) with cyclin-binding motifs PSTAIRE (CDK-a) and PPTA/TLRE (CDK-b). Tobacco (Nicotiana tabacum L. cv Bright Yellow-2) cells are the most highly synchronizable plant culture, but no detailed analysis of CDK activities has been reported in this system. Here we describe isolation of new PPTALRE CDKs (Nicta;CdkB1) from Bright Yellow-2 cells and present detailed analysis of the mRNA, protein and kinase activity levels of CdkB1, and the PSTAIRE CDKA during the growth and cell cycles. CdkA andCdkB1 transcripts are more abundant in exponential than in stationary phase cells, but the two genes show strikingly different regulation during the cell cycle. CdkA mRNA and protein accumulate during G1 in cells re-entering the cell cycle, and immunoprecipitated histone H1 kinase activity increases at the G1/S boundary. Aphidicolin synchronized cells show the highest CDKA-associated histone H1 kinase activity during S-G2 phases, althoughCdkA mRNA and protein levels are not significantly regulated. In contrast, CdkB1 transcripts are present at very low levels until S phase and CDKB1 protein and kinase activity is almost undetectable in G1. CdkB1 mRNA accumulates through S until M phase and its associated kinase activity peaks at the G2/M boundary, confirming that transcription of PPTALRE CDKs is cell cycle regulated. We suggest that CDKA kinase activity likely plays roles at the G1/S phase boundary, during S phase, and at the G2/M phase transition, and that CDKB1 kinase activity is present only at G2/M.
Cytokinin Overproducing ove Mutants ofPhyscomitrella patens Show Increased Riboside to Base Conversion
Authors: Schulz Peter A. , Hofmann Angelika H. , Russo Vincenzo E.A. , Hartmann Elmar , Laloue Michel , von Schwartzenberg Klaus 
Published: July 2002

Abstract
Ove mutants in the moss Physcomitrella patens can arise from different recessive mutations. These mutants display a much larger number of buds than the wild type (wt) due to a dramatic overproduction of cytokinins (Cks), which are released into the culture medium (T.L. Wang, R. Horgan, D.J. Cove [1981] Plant Physiol 68: 735–738). The amounts of isopentenyladenine (iP) and isopentenyladenosine ([9R]iP) produced by chloronema of different ove mutants were measured. Levels of the major Ck iP in the culture medium of the mutantsoveA78, oveA201, oveC200, and oveB300 (cultured at 21°C) were 4-fold (oveA78) to 22-fold (oveB300) higher than for the wt. A new temperature-sensitive ove strainoveST25, which exhibits a strong ovephenotype at 25°C, was also studied. It produced about 260 times more iP than the thiamine auxotrophic wt from which it was derived. To contribute to the physiological understanding of Ck overproduction, in vivo labeling experiments with 3H-[9R]iP were performed. In all ove mutants analyzed, the rate of3H-[9R]iP conversion to 3H-iP was higher as compared with the wt. In oveST25, the 3-fold increased riboside to base conversion was temperature inducible and correlated with the iP production. Analysis of Ck catabolism revealed no major differences between ove mutants and wt, thus indicating that ove mutants are unlikely to be degradation mutants. The data suggest that in ove mutants the increased riboside to base conversion is part of a generally up-regulated Ck biosynthetic pathway and may play an important role for the enhanced release of iP into the medium.
Structural and thermodynamic analysis of the binding of solvent at internal sites in T4 lysozyme
Authors: Xu Jian , Baase Walter A. , Quillin Michael L. , Baldwin Enoch P. , Matthews Brian W. 
Published: July 2002

AbstractTo investigate the structural and thermodynamic basis of the binding of solvent at internal sites within proteins a number of mutations were constructed in T4 lysozyme. Some of these were designed to introduce new solvent‐binding sites. Others were intended to displace solvent from preexisting sites. In one case Val‐149 was replaced with alanine, serine, cysteine, threonine, isoleucine, and glycine. Crystallographic analysis shows that, with the exception of isoleucine, each of these substitutions results in the binding of solvent at a polar site that is sterically blocked in the wild‐type enzyme. Mutations designed to perturb or displace a solvent molecule present in the native enzyme included the replacement of Thr‐152 with alanine, serine, cysteine, valine, and isoleucine. Although the solvent molecule was moved in some cases by up to 1.7Å, in no case was it completely removed from the folded protein. The results suggest that hydrogen bonds from the protein to bound solvent are energy neutral. The binding of solvent to internal sites within proteins also appears to be energy neutral except insofar as the bound solvent may prevent a loss of energy due to potential hydrogen bonding groups that would otherwise be unsatisfied. The introduction of a solvent‐binding site appears to require not only a cavity to accommodate the water molecule but also the presence of polar groups to help satisfy its hydrogen‐bonding potential. It may be easier to design a site to accommodate two or more water molecules rather than one as the solvent molecules can then hydrogen‐bond to each other. For similar reasons it is often difficult to design a point mutation that will displace a single solvent molecule from the core of a protein.
Structural features of interferon‐γ aggregation revealed by hydrogen exchange
Authors: Tobler Scott A. , Fernandez Erik J. 
Published: July 2002

AbstractUsing hydrogen‐deuterium exchange (HX) and electrospray ionization mass spectrometry, we have investigated the stability and structural changes of recombinant human interferon‐γ (IFN‐γ) during aggregation induced by guanidine hydrochloride (GdnHCl) and potassium thiocyanate. First, HX labeling was initiated after the amorphous aggregates were formed to probe the tertiary structure of the aggregated state. Second, labeling was performed at low protein concentrations to assess stability under aggregation prone conditions. In 1 M GdnHCl, the stability of IFN‐γ was greatly reduced and much less protection from HX in solution was observed. Exchange under these conditions was slower in helix C than in the rest of the protein. Aggregates formed in 1 M GdnHCl showed a HX pattern consistent with a partially unfolded state with an intact helix C. Although aggregates formed in 0.3 M KSCN exhibited a HX pattern similar to those formed in GdnHCl, the solution phase HX pattern in 0.3 M KSCN was surprisingly comparable to that of the native state. Varying the aggregation time before performing HX revealed that KSCN first precipitated native protein and then facilitated partial unfolding of the precipitated protein. These results show that helix C, which forms the hydrophobic core of the IFN‐γ dimer, is highly protected from HX under native conditions, is more stable in GdnHCl than the rest of the protein and remains intact in both GdnHCl‐ and KSCN‐induced aggregates. This suggests that native‐state HX patterns may presage regions of the protein susceptible to unfolding during aggregation.
Tensile Mechanical Properties of Three-Dimensional Type I Collagen Extracellular Matrices With Varied Microstructure
Authors: Roeder Blayne A. , Kokini Klod , Sturgis Jennifer E. , Robinson J. Paul , Voytik-Harbin Sherry L. 
Published: July 2002

AbstractThe importance and priority of specific micro-structural and mechanical design parameters must be established to effectively engineer scaffolds (biomaterials) that mimic the extracellular matrix (ECM) environment of cells and have clinical applications as tissue substitutes. In this study, three-dimensional (3-D) matrices were prepared from type I collagen, the predominant compositional and structural component of connective tissue ECMs, and structural-mechanical relationships were studied. Polymerization conditions, including collagen concentration (0.3–3 mg/mL) and pH (6–9), were varied to obtain matrices of collagen fibrils with different microstructures. Confocal reflection microscopy was used to assess specific micro-structural features (e.g., diameter and length) and organization of component fibrils in 3-D. Microstructural analyses revealed that changes in collagen concentration affected fibril density while maintaining a relatively constant fibril diameter. On the other hand, both fibril length and diameter were affected by the pH of the polymerization reaction. Mechanically, all matrices exhibited a similar stress-strain curve with identifiable “toe,” “linear,” and “failure” regions. However, the linear modulus and failure stress increased with collagen concentration and were correlated with an increase in fibril density. Additionally, both the linear modulus and failure stress showed an increase with pH, which was related to an increased fibril length and a decreased fibril diameter. The tensile mechanical properties of the collagen matrices also showed strain rate dependence. Such fundamental information regarding the 3-D microstructural-mechanical properties of the ECM and its component molecules are important to our overall understanding of cell-ECM interactions (e.g., mechanotransduction) and the development of novel strategies for tissue repair and replacement.
In Vitro Activities of the Ketolides Telithromycin (HMR 3647) and HMR 3004 Compared to Those of Clarithromycin against Slowly Growing Mycobacteria at pHs 6.8 and 7.4
Authors: Rastogi Nalin , Goh Khye Seng , Berchel Mylene , Bryskier André 
Published: July 2002

ABSTRACT

The in vitro activities of HMR 3647 (telithromycin) and HMR 3004, two novel semisynthetic ketolides, were investigated and compared with that of the reference macrolide drug, clarithromycin, against 34 strains of slowly growing mycobacteria at pHs 6.8 and 7.4, as determined radiometrically. The MICs at pH 7.4 were about 1 to 2 dilutions lower than those observed at pH 6.8. In terms of the highest to the lowest activity, the three antibiotics could be classified as follows: clarithromycin > HMR 3004 > HMR 3647. Among the species tested,
Mycobacterium bovis
BCG,
M. ulcerans
,
M. avium
, and
M. paratuberculosis
were moderately susceptible to HMR 3004 and HMR 3647 (MICs at pH 7.4, ≤5.0 and ≤20.0 μg/ml, respectively, versus ≤1.25 μg/ml for clarithromycin), whereas
M. tuberculosis
,
M. africanum
,
M. bovis
, and
M. simiae
were resistant (MICs, ≥10.0 and ≥40.0 μg/ml, respectively, at pH 7.4). Although not more active than clarithromycin in vitro, the high level of intracellular accumulation of the two ketolides inside phagocytes warrants further screening in experimental animal models.
Undecylenic Acid Inhibits Morphogenesis of
Candida albicans
Authors: McLain Nealoo , Ascanio Rhoda , Baker Carol , Strohaver Robert A. , Dolan Joseph W. 
Published: July 2002

ABSTRACT

Resilient liners are frequently used to treat denture stomatitis, a condition often associated with
Candida albicans
infections. Of 10 liners tested, 2 were found to inhibit the switch from the yeast form to hyphae and a third was found to stimulate this switch. The inhibitor was determined to be undecylenic acid.
Identification of the Coumermycin A
1
Biosynthetic Gene Cluster of
Streptomyces rishiriensis
DSM 40489
Authors: Wang Zhao-Xin , Li Shu-Ming , Heide Lutz 
Published: July 2002

ABSTRACT

The biosynthetic gene cluster of the aminocoumarin antibiotic coumermycin A
1
was cloned by screening of a cosmid library of
Streptomyces rishiriensis
DSM 40489 with heterologous probes from a dTDP-glucose 4,6-dehydratase gene, involved in deoxysugar biosynthesis, and from the aminocoumarin resistance gyrase gene
gyrB
r
. Sequence analysis of a 30.8-kb region upstream of
gyrB
r
revealed the presence of 28 complete open reading frames (ORFs). Fifteen of the identified ORFs showed, on average, 84% identity to corresponding ORFs in the biosynthetic gene cluster of novobiocin, another aminocoumarin antibiotic. Possible functions of 17 ORFs in the biosynthesis of coumermycin A
1
could be assigned by comparison with sequences in GenBank. Experimental proof for the function of the identified gene cluster was provided by an insertional gene inactivation experiment, which resulted in an abolishment of coumermycin A
1
production.
In Vitro Susceptibility Tests for Cationic Peptides: Comparison of Broth Microdilution Methods for Bacteria That Grow Aerobically
Authors: Giacometti A. , Cirioni O. , Barchiesi F. , Del Prete M. S. , Fortuna M. , Caselli F. , Scalise G. 
Published: July 2002

ABSTRACT
The in vitro susceptibilities of 90 clinical isolates of gram-positive and gram-negative aerobic bacteria to six cationic peptides, buforin II, cecropin P1, indolicidin, magainin II, nisin, and ranalexin, were evaluated by two broth microdilution methods. The first method was performed according to the procedures outlined by the National Committee for Clinical Laboratory Standards for bacteria that grow aerobically, while the second was performed according to the procedures recently proposed by the R. E. W. Hancock laboratory for testing antimicrobial peptides. Overall, the first method produced MICs two- and fourfold higher than the second method.
Stenotrophomonas maltophiliaD457R Contains a Cluster of Genes from Gram-Positive Bacteria Involved in Antibiotic and Heavy Metal Resistance
Authors: Alonso Ana , Sanchez Patricia , Martínez José L. 
Published: July 2002

ABSTRACTA cluster of genes involved in antibiotic and heavy metal resistance has been characterized from a clinical isolate of the gram-negative bacteriumStenotrophomonas maltophilia. These genes include a macrolide phosphotransferase (mphBM) and a cadmium efflux determinant (cadA), together with the genecadCcoding for its transcriptional regulator. ThecadC cadAregion is flanked by a truncated IS257sequence and a region coding for abin3invertase. Despite their presence in a gram-negative bacterium, these genetic elements share a common gram-positive origin. The possible origin of these determinants as a remnant composite transposon as well as the role of gene transfer between gram-positive and gram-negative bacteria for the acquisition of antibiotic resistance determinants in chronic, mixed infections is discussed.
Antimicrobial Resistance and Spread of Class 1 Integrons among
Salmonella
Serotypes
Authors: Guerra Beatriz , Soto Sara , Cal Santiago , Mendoza M. Carmen 
Published: July 2002

ABSTRACT

The resistance profiles, for 15 antimicrobial agents, of 333
Salmonella
strains representing the most frequent nontyphoidal serotypes, isolated between 1989 and 1998 in a Spanish region, and 9 reference strains were analyzed. All strains were susceptible to amikacin, ceftazidime, ciprofloxacin, and imipenem, and 31% were susceptible to all antimicrobials tested. The most frequent types of resistance were to sulfadiazine, tetracycline, streptomycin, spectinomycin, ampicillin, and chloramphenicol (ranging from 46 to 22%); 13% were resistant to these six drugs. This multidrug resistance pattern was found alone or together with other resistance types within serotypes Typhimurium (45%), Panama (23%), and Virchow (4%). Each isolate was also screened for the presence of class 1 integrons and selected resistance genes therein; seven variable regions which carried one (
aadA1a
,
aadA2
, or
pse-1
) or two (
dfrA14-aadA1a
,
dfrA1-aadA1a
,
oxa1-aadA1a
, or
sat1-aadA1a
) resistance genes were found in integrons.
Mutation in 23S rRNA Responsible for Resistance to 16-Membered Macrolides and Streptogramins in
Streptococcus pneumoniae
Authors: Depardieu Florence , Courvalin Patrice 
Published: July 2002

ABSTRACT

Streptococcus pneumoniae
clinical isolate BM4455 was resistant to 16-membered macrolides and to streptogramins. This unusual resistance phenotype was due to an A
2062
C (
Escherichia coli
numbering) mutation in domain V of the four copies of 23S rRNA.
Emergence of Reduced Susceptibility and Resistance to Fluoroquinolones in
Escherichia coli
in Taiwan and Contributions of Distinct Selective Pressures
Authors: McDonald L. Clifford , Chen Feng-Jui , Lo Hsiu-Jung , Yin Hsiao-Chuan , Lu Po-Liang , Huang Cheng-Hua , Chen Pei , Lauderdale Tsai-Ling , Ho Monto 
Published: July 2002

ABSTRACT

A survey of 1,203
Escherichia coli
isolates from 44 hospitals in Taiwan revealed that 136 (11.3%) isolates were resistant to fluoroquinolones and that another 261 (21.7%) isolates had reduced susceptibility. Resistance was more common in isolates responsible for hospital-acquired (mostly in intensive care units) infections (17.5%) than in other adult inpatient (11.4%;
P
= 0.08) and outpatient isolates (11.9%;
P
> 0.1). Similarly, reduced susceptibility was more common in isolates responsible for hospital-acquired infections (30.9%) than in other adult inpatient (21.0%;
P
= 0.04) and outpatient (21.4%;
P
= 0.06) isolates. Isolates from pediatric patients were less likely to be resistant (1.3 versus 12.0%;
P
< 0.01) but were nearly as likely to have reduced susceptibility (17.7 versus 21.9%;
P
> 0.1) as nonpediatric isolates. There was an inverse relationship in the proportion of isolates that were resistant versus the proportion that had reduced susceptibility among isolates from individual hospitals (
R
= 0.031; P < 0.05). In an analysis of isolates from two hospitals, all 9 resistant strains possessed double point mutations in
gyrA
and all 19 strains with reduced susceptibility strains had single point mutations; no mutations were found among fully susceptible strains. Risk factors for resistance included underlying cancer (odds ratio [OR], 83; 95% confidence interval [CI
95
], 7.3 to 2,241;
P
< 0.001), exposure to a quinolone (OR, undefined;
P
= 0.02), and exposure to a nonquinolone antibiotic (OR, 20; CI
95
, 2.2 to 482;
P
< 0.001); underlying cancer was the only independent risk factor (OR, 83; CI
95
, 8.6 to 807;
P
< 0.001). There were no significant associations between any of these factors and reduced susceptibility. Whereas acute and chronic quinolone use in cancer patients is a major selective pressure for resistance, other undetermined but distinct selective pressures appear to be more responsible for reduced susceptibility to fluoroquinolones in
E. coli
.