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PubMed2004

Divergence in noncognate amino acid recognition between class I and class II lysyl-tRNA synthetases.

Lysine insertion during coded protein synthesis requires lysyl-tRNA(Lys), which is synthesized by lysyl-tRNA synthetase (LysRS). Two unrelated forms of LysRS are known: LysRS2, which is found in eukaryotes, most bacteria, and a few archaea, and LysRS1, which is found in most archaea and a few bacteria. To compare amino acid recognition between the two forms of LysRS, the effects of l-lysine analogues on aminoacylation were investigated. Both enzymes showed stereospecificity toward the l-enantiomer of lysine and discriminated against noncognate amino acids with different R-groups (arginine, ornithine). Lysine analogues containing substitutions at other positions were generally most effective as inhibitors of LysRS2. For example, the K(i) values for aminoacylation of S-(2-aminoethyl)-l-cysteine and l-lysinamide were over 180-fold lower with LysRS2 than with LysRS1. Of the other analogues tested, only gamma-aminobutyric acid showed a significantly higher K(i) for LysRS2 than LysRS1. These data indicate that the lysine-binding site is more open in LysRS2 than in LysRS1, in agreement with previous structural studies. The physiological significance of divergent amino acid recognition was reflected by the in vivo resistance to growth inhibition imparted by LysRS1 against S-(2-aminoethyl)-l-cysteine and LysRS2 against gamma-aminobutyric acid. These differences in resistance to naturally occurring noncognate amino acids suggest the distribution of LysRS1 and LysRS2 contributes to quality control during protein synthesis. In addition, the specific inhibition of LysRS1 indicates it is a potential drug target.

Amino Acids↗
PubMed1982

T cell regulation of immunoglobulin class expression in the antibody response to trinitrophenyl-ficoll. Evidence for T cell enhancement of the immunoglobulin class switch.

In the absence of T cells, B cells were found to respond to the type 2 T-independent (TI-2) antigen, trinitrophenyl (TNP)-Ficoll, with a characteristic hierarchy of IgM and IgG subclass Ab production which directly correlated with 5' to 3' Igh-C gene order, i.e., IgM greater tha IgG3 greater than IgG1 greater than IgG2b greater than IgG2a. This was evident when immune serum Ab titers were analyzed, when in vitro secretion of antibody from immune cells was measured and when TNP-Ficoll-stimulated clones in a splenic focus assay were analyzed for isotype production. T cells were found to cause a preferential relative increase in the amount of IgG2a antibody produced to TNP-Ficoll. The T cell responsible was present in anti-IgM neonatally suppressed mice and was needed early in the response, i.e., on the day of immunization or earlier. T cells were found to increase the frequency of TNP-Ficoll-responsive B cell clones that produced IgG2a in the splenic focus assay. The great majority of these IgG2a-positive clones also produced IgM and all or nearly all of the IgG isotypes whose genes are encoded 5' to the Igh-gamma 2a gene. The data are discussed in terms to T cell enhancement of IgG2a Ab synthesis being mediated through T cell enhancement of the Igh-C gene switching mechanism within TNP-Ficoll-responsive B cell clones. Thus, isotypes encoded by genes on the 3' end of the Igh-gamma gene complex, which in the absence of T cells have a low probability of being switched to, are the most influenced by T cell help.

Animals↗
PubMed2004

Association of human-leukocyte-antigen class I (B*0703) and class II (DRB1*0301) genotypes with susceptibility and resistance to the development of severe acute respiratory syndrome.

Severe acute respiratory syndrome (SARS) is a public health concern worldwide. By studying the human leukocyte antigen (HLA) types A, B, DR, and DQ alleles in 90 Chinese patients with serologically confirmed SARS infections, we identified a strong association between HLA-B*0703 (OR, 4.08; 95% CI, 2.03-8.18; P=.00072 [Bonferroni-corrected P value, P(c) <.0022]) and -DRB1*0301 (OR, 0.06; 95%, 0.01-0.47; P=.00008 [after Bonferroni correction, P<.0042]) and the development of SARS. Moreover, the frequency of B*0703 and B60 coinheritance (9.6%; 95% CI, 4.6%-19.0%) in our SARS group was significantly higher (P=3x10(-9)) than that expected in the general population (0.4%). These genetic data will critically affect both the study of the pathogenesis of SARS and the design of vaccination programs.

Adult↗
PubMed1998

Treatment changes in Class I and mild Class II malocclusions using the en masse removable appliance.

The aim of this retrospective study was to examine the dental changes which occurred during buccal segment retraction in 39 subjects considered suitable for treatment with headgear to the maxillary dentition. Initially, a removable en masse appliance was fitted to distalize the buccal segments. Once the molar relationship was corrected, fixed appliances were placed for upper arch consolidation and/or alignment. Only five subjects required lower appliance therapy. Twenty-nine individuals had upper second molars extracted as an adjunct to treatment: in the remaining 10 patients these teeth were left in situ. Corresponding lower second molars were extracted in 19 children, whilst 20 pairs of teeth were not removed. Measurements were made at the start of treatment, the completion of buccal segment retraction, and when active treatment was complete. After the first stage, molars and premolars had been retracted nearly 4 mm, whilst the canines showed 2 mm spontaneous distal drift. The inter-molar width had increased by 4 mm and arch perimeter by 5 mm. There was a 5 per cent reduction in crowding. Spontaneous changes were also seen in the lower arch, despite the absence of any therapy. Crowding was slightly improved and inter-molar width increased, apparently as a response to the expansion in the opposing jaw. At the end of treatment, upper arch retraction and expansion were reduced as the teeth were integrated with the lower dentition: the canines required less than 1 mm further retraction. In the lower arch, the expansion of the molars was essentially stable. The extraction of upper second molars did not appear to influence the outcome of treatment. Although slightly more movement appeared to occur in the extraction group, few measurements showed statistical significance.

Adolescent↗
PubMedDate not supplied

Factors influencing the specialty choice of the physical medicine and rehabilitation graduating class of 1994 and the entering class of 1995.

To understand better how career choices are made by physiatrists, a 16-item, 7-page questionnaire was sent to all 1994 graduating physical medicine and rehabilitation (PM&R) resident physicians in the United States. Of the 343 senior residents, 202 completed the questionnaire for a response rate of 59%. The questionnaire focused on the following areas: timing of the decision to enter PM&R; and how the medical school curriculum, certain groups of people, and certain specific factors influenced their choices. There were 130 factors modeled after the American Association of Medical Colleges (AAMC) annual medical student questionnaire that the recipients were asked to grade on a numerical scale: 1 = unimportant to 5 = very important. Of the graduating residents, 60.1% (119/198) made the decision to enter PM&R in their 3rd or 4th yr of medical school, 13.1% (26/198) in the first 2 yr, and 11.1% (22/198) after starting another residency. The five factors ranked most important in the decision were (mean rank score): sufficient time/flexibility for family obligations (4.60); opportunity to make a difference in peoples lives (4.57); interest in helping people (4.55); types of patient problems encountered (4.50); and consistency with personality (4.49). We also obtained the AAMC's 1993 annual data on medical students choosing PM&R. Their top five factors were the same as those listed by the graduating residents, but in a slightly different rank order. Profiles have also been derived on those graduating PM&R residents who chose an academic career (n = 68) v nonacademic (n = 133) and fellowship (n = 34) v nonfellowship (n = 163).

Career Choice↗
PubMed1991

Effects of hyperkalemia, acidosis, and hypoxia on the depression of maximum rate of depolarization by class I antiarrhythmic drugs in guinea pig myocardium: differential actions of class Ib and Ic agents.

Standard microelectrode methods were used to record intracellular action potentials from strips of guinea pig right ventricular myocardium superfused with either standard physiological saline (pH 7.3; PO2 greater than 650 mm Hg; [K+] = 5.6 mM) or the same solution modified to produce either hyperkalemia ([ K+] = 11.2 mM), acidosis (pH = 6.3), or hypoxia (PO2 = 60 mm Hg). The effects on action potential parameters of three therapeutic concentration of lidocaine, flecainide, and encainide were studied under all four conditions at four different drive rates (interstimulus interval = 2,400, 1,200, 600, and 300 ms). Hyperkalemia in the absence of drugs produced reductions in resting potential (-87.9 +/- 3.8 to -74.6 +/- 3.3 mV), maximum rate of depolarization (316 +/- 68 to 240 +/- 12 V/s), and action potential duration (178 +/- 21 to 165 +/- 27 ms). All three drugs produced increased depression of Vmax in hyperkalemia compared to control conditions but, at all three concentrations and all four rates, this enhancement of effect was greater for lidocaine than for either of the other two agents (which did not differ significantly from each other; p less than 0.001). Similar though less marked effects were produced by acidosis (3.5 mV depolarization and 19% reduction in Vmax), and once again the depression of Vmax by lidocaine was enhanced more by this intervention than were the actions of encainide or flecainide (p less than 0.01). Hypoxia had no effect on action potential parameters other than duration and no significant modulation of drug actions was seen for this intervention.(ABSTRACT TRUNCATED AT 250 WORDS)

Acidosis↗
PubMed1993

Sustained atrial flutter around the tricuspid valve in pigs: differentiation of procainamide (class IA) from flecainide (class IC) and their rate-dependent effects.

The wavelength theory considers two determinants of reentry, i.e., refractoriness and conduction velocity. It does not take excitability into account primarily. We evaluated frequency-dependence of excitability and refractoriness before and after flecainide or procainamide administration in relation to termination of reentrant atrial flutter. After making a Y-shaped lesion in the right atrium, we induced 62 flutters (cycle length 171 +/- 15 ms) by electrical stimulation in 15 pigs. Strength-interval curves were determined to assess excitability and refractoriness. Multiple cycle lengths were used to establish rate-dependent changes. Flutter cycle length increased after flecainide (to 290 +/- 67 ms) or procainamide (to 295 +/- 54 ms). The flutters always terminated abruptly (flecainide dose 103 +/- 104 mg, plasma concentration 370 +/- 21 ng/ml; procainamide dose 1,150 +/- 686 mg, concentration 51 +/- 24 mg/l). Flecainide caused an increase in diastolic thresholds from 0.3 +/- 0.2 to 0.8 +/- 0.5 mA (p < 0.006) and procainamide from 0.5 +/- 0.3 to 0.9 +/- 0.5 mA (p < 0.02). The increase in threshold was frequently dependent. Procainamide increased refractoriness at longer cycle lengths (> or = 250 ms), but this effect was abolished at shorter cycle lengths, indicating that only after significant slowing of the rate, prolongation of refractoriness may appear. Thus, both drugs interrupt reentrant flutter mainly by reducing excitability. Subclassification into IA and IC may be less relevant at high rates. Construction of strength-interval curves and assessment of rate-dependent "postrepolarization refractoriness" should be considered when one studies drugs that influence excitability.

Animals↗
PubMedDate not supplied

Designing and facilitating class discussion in an Internet class.

Designing a replacement for face-to-face classroom discussion is a major consideration in the development of an Internet course, whether the course is completely new or a redesign of an existing course. The experiences of four faculty members who were involved in developing courses for a baccalaureate completion program for RNs taught entirely on the Internet will be used to illustrate key issues in designing andfacilitating on-line discussion.

Communication↗
PubMed1984

Cell-mediated cytotoxicity toward class I and class II antigens on canine T and B lymphoblasts.

Cellular cytotoxicity generated in vitro has been studied with canine T and B lymphoblasts as target cells. B lymphocytes were isolated by rosetting with protein A labeled sheep red blood cells and stimulated with sepharose bound protein A. Such highly purified stimulated B lymphoblasts appeared to be useful target cells for cellular cytotoxicity. Cold target inhibition studies and limiting dilution analysis revealed that B lymphocytes did not carry targets for cytotoxic T lymphocytes (CTL) which were not present on PHA stimulated T lymphoblasts.

Animals↗