Posttranscriptional modifications of ribosomal RNA (rRNA) nucleotides are a common mechanism of modulating the ribosome’s function and conferring bacterial resistance to ribosome-targeting ...antibiotics. One such modification is methylation of an adenosine nucleotide within the peptidyl transferase center of the ribosome mediated by the endogenous methyltransferase RlmN and its evolutionarily related resistance enzyme Cfr. These methyltransferases catalyze methyl transfer to aromatic carbon atoms of the adenosine within a complex 23S rRNA substrate to form the 2,8-dimethylated product. RlmN and Cfr are members of the Radical SAM superfamily and contain the characteristic cysteine-rich CX3CX2C motif. We demonstrate that both enzymes are capable of accommodating the requisite 4Fe-4S cluster. S-Adenosylmethionine (SAM) is both the methyl donor and the source of a 5′-deoxyadenosyl radical, which activates the substrate for methylation. Detailed analyses of the rRNA requirements show that the enzymes can utilize protein-free 23S rRNA as a substrate, but not the fully assembled large ribosomal subunit, suggesting that the methylations take place during the assembly of the ribosome. The key recognition elements in the 23S rRNA are helices 90−92 and the adjacent single stranded RNA that encompasses A2503. To our knowledge, this study represents the first in vitro description of a methyl transfer catalyzed by a member of the Radical SAM superfamily, and it expands the catalytic repertoire of this diverse enzyme class. Furthermore, by providing information on both the timing of methylation and its substrate requirements, our findings have important implications for the functional consequences of Cfr-mediated modification of rRNA in the acquisition of antibiotic resistance.
Researchers have observed differences in muscle activity patterns between males and females during functional exercises. The research methods employed have used various step heights and lunge ...distances to assess functional exercise making gender comparisons difficult. The purpose of this study was to examine core and lower extremity muscle activity between genders during single-limb exercises using adjusted distances and step heights based on a percentage of the participant's height.
Twenty men and 20 women who were recreationally active and healthy participated in the study. Two-dimensional video and surface electromyography (SEMG) were used to assess performance during three exercise maneuvers (step down, forward lunge, and side-step lunge). Eight muscles were assessed using SEMG (rectus abdominus, external oblique, erector spinae, rectus femoris, tensor fascia latae, gluteus medius, gluteus maximus, biceps femoris). Maximal voluntary isometric contractions (MVIC) were used for each muscle and expressed as %MVIC to normalize SEMG to account for body mass differences. Exercises were randomized and distances were normalized to the participant's lower limb length. Descriptive statistics, mixed-model ANOVA, and ICCs with 95% confidence intervals were calculated.
Males were taller, heavier, and had longer leg length when compared to the females. No differences in %MVIC activity were found between genders by task across the eight muscles. For both males and females, the step down task resulted in higher %MVIC for gluteus maximus compared to lunge, (p=0.002). Step down exercise produced higher %MVIC for gluteus medius than lunge (p=0.002) and side step (p=0.006). ICC(3,3) ranged from moderate to high (0.74 to 0.97) for the three tasks.
Muscle activation among the eight muscles was similar between females and males during the lunge, side-step, and step down tasks, with distances adjusted to leg length. Both males and females elicited higher muscle activity for gluteus maximus and gluteus medius as compared to the trunk, hip flexors, or hamstring muscles. However these values were well below the recruitment levels necessary for strengthening in both genders.
4.
1 Baker Heart Research Institute and 2 Department of Medicine, Central and Eastern Clinical School, Monash University, and 3 Department of Pharmacology, Melbourne University, Melbourne, Victoria ...8008, Australia
Submitted 30 October 2003
; accepted in final form 11 January 2004
The link between the human sympathoadrenalmedullary system and the adipocyte hormone leptin is controversial. We measured total and regional norepinephrine spillover, epinephrine secretion rate, and extra-adipocyte leptin release in 22 lean body mass index (BMI) <26 and 20 obese (BMI >28) normotensive men who underwent arterial and central venous catheterization. Because plasma clearance of leptin is primarily by renal removal, for men at steady state we could estimate whole body leptin release to plasma from renal plasma leptin extraction. Whole body leptin release was 1,950 ± 643 (means ± SE) ng/min in obese men and 382 ± 124 ng/min in lean men ( P < 0.05). Total and renal norepinephrine spillover rates correlated directly with whole body leptin secretion rate. Leptin is released from multiple nonadipocyte sites, which we tested by use of simultaneous arteriovenous blood sampling. We found a surprisingly large contribution of brain leptin release to the plasma leptin pool, 529 ± 175 ng/min (>40% whole body leptin release), with greater leptin release in obese than in lean men, 935 ± 321 vs. 160 ± 59 ng/min ( P = 0.045). In parallel with leptin measurements, we also quantified brain serotonin turnover and jugular overflow of neuropeptide Y (NPY). Brain serotonin turnover was higher in obese than in lean men, 227 ± 112 vs. 21 ± 14 ng/min ( P = 0.019), as was overflow of NPY from the brain, 12.9 ± 1.4 vs. 5.3 ± 2.2 ng/min ( P = 0.042). These results suggest that leptin is released within the brain and at an increased rate in obese humans, in whom activation of brain serotonergic and NPY mechanisms also exists.
leptin; norepinephrine spillover; epinephrine secretion rate; 5-hydroxyindoleacetic acid; neuropeptide Y
Address for reprint requests and other correspondence: M. Esler, Baker Heart Research Institute, PO Box 6492, St. Kilda Road Central, Melbourne, Victoria 8008, Australia (E-mail: murray.esler{at}baker.edu.au ).
Since the brain neurotransmitter changes characterising panic disorder remain uncertain, we quantified brain noradrenaline and serotonin turnover in patients with panic disorder, in the absence of a ...panic attack. Thirty-four untreated patients with panic disorder and 24 matched healthy volunteers were studied. A novel method utilising internal jugular venous sampling, with thermodilution measurement of jugular blood flow, was used to directly quantify brain monoamine turnover, by measuring the overflow of noradrenaline and serotonin metabolites from the brain. Radiographic depiction of brain venous sinuses allowed differential venous sampling from cortical and subcortical regions. The relation of brain serotonin turnover to serotonin transporter genotype and panic disorder severity were evaluated, and the influence of an SSRI drug, citalopram, on serotonin turnover investigated.
Brain noradrenaline turnover in panic disorder patients was similar to that in healthy subjects. In contrast, brain serotonin turnover, estimated from jugular venous overflow of the metabolite, 5-hydroxyindole acetic acid, was increased approximately 4-fold in subcortical brain regions and in the cerebral cortex (P < 0.01). Serotonin turnover was highest in patients with the most severe disease, was unrelated to serotonin transporter genotype, and was reduced by citalopram (P < 0.01). Normal brain noradrenaline turnover in panic disorder patients argues against primary importance of the locus coeruleus in this condition. The marked increase in serotonin turnover, in the absence of a panic attack, possibly represents an important underlying neurotransmitter substrate for the disorder, although this point remains uncertain. Support for this interpretation comes from the direct relationship which existed between serotonin turnover and illness severity, and the finding that SSRI administration reduced serotonin turnover. Serotonin transporter genotyping suggested that increased whole brain serotonin turnover most likely derived not from impaired serotonin reuptake, but from increased firing in serotonergic midbrain raphe neurons projecting to both subcortical brain regions and the cerebral cortex.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Autoantibodies observed in patients with rheumatoid arthritis (RA) during clinical trials of immunomodulating agents may cause concern about possible induction of autoimmunity by the therapeutic ...intervention. We determined the frequency and variability of selected autoantibodies in patients with early rheumatoid factor (RF) positive RA during a prospective observational study.
The study cohort consisted of 276 patients with active RA and with RF > or = 40 IU, who were enrolled between January 1, 1993, and April 1, 2000, before starting disease modifying antirheumatic drug (DMARD) therapy (average duration of symptoms, 7 mo). During an average of 3.5 years followup, a panel of autoantibodies was determined at entry, 6 months, 12 months, and yearly thereafter, in addition to routine clinical, radiographic, and laboratory assessments. After enrollment, patients were treated with DMARD at the discretion of their rheumatologists.
At entry before any DMARD therapy, antinuclear antibody (ANA; by HEp-2) values were negative in 31%, borderline (8 IU/ml) in 26%, and > 8 (mean 65.5 IU/ml) in 41%. Tender and swollen joint counts, Disease Activity Score, and RF values were significantly higher in those with ANA > 8. During followup 726 paired serial specimens were available; 12.5% changed from negative to positive ANA and 12.3% from positive to negative. Additional autoantibodies were present in specimens of 20% of the subjects; 8% had 2 and 1.4% had 3 other autoantibodies. Anti-dsDNA was detected in 13 (5.5%) patients; 4 changed from negative to positive and one from positive to negative. SSA IgG and SSB IgG autoantibodies were both present in one of these patients. Ribosomal P protein autoantibodies were noted in 2 other patients, but Sm (Smith) and uRNP/snRNP IgG autoantibodies were not present in any patient. No patient had a diagnosis of systemic lupus erythematosus. Antithyroid peroxidase (20 patients), parietal cell (15), smooth muscle (14), reticulin (9), mitochondrial (5), striational (2), SSB (2) and SCL-70 (1) autoantibodies were detected in some specimens. Seven patients were diagnosed with hypothyroidism, one with chronic thyroiditis, one with hepatitis C, and 9 with malignancies.
In patients with early RF positive RA the frequent occurrence of autoantibodies before and during treatment with standard DMARD may make it difficult to attribute their presence to new therapies.
The 16-kDa polypeptide hormone, leptin along with the neurotransmitters noradrenaline and serotonin (5-HT) have important physiological roles in the regulation of a number of neuroendocrine actions ...particularly feeding. Leptin receptor mRNA and immunoreactivity has been reported in various brain regions, while recent studies suggest that leptin is released from the human brain. This study investigated the interactions between leptinergic and neurotransmitter systems of the rat brain in vitro. Techniques were established to simultaneously monitor the release of endogenous noradrenaline and its metabolite 3,4 dihydroxyphenylglycol (DHPG), and 5-HT and its metabolite 5-hydroxyindoleacetic acid (5-HIAA) from the rat brain. The neuromodulatory action of leptin (0.2 and 3 nM) on the overflow of noradrenaline and DHPG from the medulla and hypothalamus was examined. The effect of leptin on 5-HT and 5-HIAA overflow from the hypothalamus was also investigated. Administration of 0.2 and 3 nM leptin significantly increased medullary noradrenaline overflow to 172% and 174% of basal levels, respectively. Leptin had no significant effect on hypothalamic noradrenaline overflow, while leptin perfusion induced a significant increase in 5-HIAA overflow from the hypothalamus. This study lends support to the notion of a complex interaction of the leptinergic and brain neurotransmitters involved in the control of feeding and energy metabolism.
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