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Biomedical subjects

K Johns

Publications and source records attributed to K Johns.

At least 19 recordsLinked to original sources
PubMed2005

Anabolic steroids for the treatment of weight loss in HIV-infected individuals.

BACKGROUND: Individuals with HIV infection often lose weight during the course of their disease. Furthermore, low serum concentrations of testosterone are common in individuals with HIV infection, particularly those with weight loss. Treatment of weight loss with anabolic steroids in HIV-infected individuals may be beneficial. OBJECTIVES: Our objectives were to assess the efficacy and safety of anabolic steroids for the treatment of weight loss in adults with HIV infection. SEARCH STRATEGY: We searched the following databases: Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, AIDSLINE, AIDSearch, EMBASE, CINAHL, Current Contents, and the National Library of Medicine Gateway Abstracts for controlled trials up to April 2005. We also searched the bibliographies of the identified studies and review the articles. In addition, pharmaceutical manufacturers of anabolic steroids were contacted. SELECTION CRITERIA: Randomized controlled trials that compared the use of an anabolic steroid to placebo to treat weight loss in adults with HIV were included. Randomized controlled trials that compared the use of anabolic steroids to placebo for the treatment of weight loss in adults with HIV were selected. Change from baseline in lean body mass or in body weight was reported as on outcome measure. DATA COLLECTION AND ANALYSIS: Two reviewers independently assessed the trials for quality of randomization, blinding, withdrawals, and adequacy of allocation concealment. For continuous data, weighted mean differences (WMD) were calculated. For dichotomous outcomes, risk differences, were calculated. Because of uncertainty as to whether consistent true effects exist in such different populations and treatments, the authors decided a priori to use random effects models for all outcomes. MAIN RESULTS: Thirteen trials met the inclusion criteria. Two hundred ninety-four individuals randomized to anabolic steroid therapy and 238 individuals randomized to placebo were included in the analysis of efficacy for change from baseline in lean body mass. Three hundred forty-three individuals randomized to anabolic steroid and 286 randomized to placebo were included in the analysis of efficacy for change from baseline in body weight. The mean methodologic quality of the included studies was 4.1, of a maximum 5 points. Although significant heterogeneity was present for both outcomes, the average change in lean body mass was 1.3 kg (95% CI: 0.6, 2.0), while the average change in total body weight was 1.1 kg (95% CI: 0.3, 2.0). A total of eight deaths occurred during the treatment period; four in the anabolic steroid treatment groups and four in the placebo-treatment groups (risk difference 0.00, 95% CI -0.03, 0.03). The risk difference for withdrawals or discontinuations of study medication due to adverse events was 0.00 (95% CI: -0.02, 0.03). AUTHORS' CONCLUSIONS: Although the results of the trials were heterogeneous, on average, the administration of anabolic steroids appeared to result in a small increase in both lean body mass and body weight as compared with placebo. While these results suggest that anabolic steroids may be useful in the treatment of weight loss in HIV infected individuals, due to limitations, treatment recommendations cannot be made. Further information is required regarding the long-term benefit and adverse effects of anabolic steroid use, the specific populations for which anabolic steroid therapy may be most beneficial, and the optimal regime. In addition, the correlation of improvement in lean body mass with more clinically relevant endpoints, such as physical functioning and survival, needs to be determined.

Anabolic Agents↗
PubMed2003

Measurement of decay parameters for Xi- --> Lambda pi- decay.

Based on 1.35 x 10(6) polarized Xi(-) events, we measure the parameter phi(Xi) to be -1.61 degrees +/-2.66 degrees +/-0.37 degrees for the Xi(-)-->Lambda pi(-) decay. New results for the parameters beta(Xi) and gamma(Xi) are also presented. Assuming that the CP-violating phase difference is negligible, we deduce the strong phase difference between the P-wave and S-wave amplitudes of the Lambda pi final state to be 3.17 degrees +/-5.28 degrees +/-0.73 degrees, reducing the uncertainty in estimating the level of CP violation in Xi-hyperon decay.

Journal Article↗
PubMed2001

Item-cued directed forgetting of related words and pictures in children and adults: selective rehearsal versus cognitive inhibition.

The main purpose of this study was to compare the relative importance of selective rehearsal and cognitive inhibition in accounting for developmental changes in the directed-forgetting paradigm developed by R. A. Bjork (1972). In two experiments, children in Grades 2 and 5 and college students were asked to remember some words or pictures and to forget others when items were categorically related. Their memory for both items and the associated remember or forget cues was then tested with recall and recognition. Fifth graders recognized more of the forget-cued words than college students did. The pattern of results suggested that age differences in rehearsal and source monitoring (i.e., remembering whether a word had been cued remember or forget) were better explanatory mechanisms for children's forgetting inefficiencies than retrieval inhibition was. The results are discussed in terms of a multiple process view of inhibition.

Adolescent↗
PubMed2000

Search for direct CP violation in nonleptonic decays of charged Xi and lambda hyperons

A search for direct CP violation in the nonleptonic decays of hyperons has been performed. In comparing the product of the decay parameters, alpha(Xi)alpha(Lambda), in terms of an asymmetry parameter, A(XiLambda), between hyperons and antihyperons in the charged Xi-->Lambdapi and Lambda-->ppi decay sequence, we found no evidence of direct CP violation. The parameter A(XiLambda) was measured to be 0.012+/-0.014.

Journal Article↗
PubMed1997

A single chain Fv fragment of P-glycoprotein-specific monoclonal antibody C219. Design, expression, and crystal structure at 2.4 A resolution.

A construct encoding a single chain variable fragment of the anti-P-glycoprotein monoclonal antibody C219 was made by combining the coding sequences for the heavy and light chain variable domains with a sequence encoding the flexible linker (GGGGS)3, an OmpA signal sequence, a c-myc identification tag, and a five-histidine purification tag. The construct was expressed in Escherichia coli and purified from the periplasmic fraction using a nickel chelate column and ion exchange chromatography. Three-step Western blot analysis showed that the construct retains binding affinity for P-glycoprotein. Crystals of 1.0 x 0.2 x 0.2 mm were grown in 100 mM citrate, pH 4.5, 21% polyethylene glycol 6000 in the presence of low concentrations of subtilisin, resulting in proteolytic removal of the linker and purification tags. The structure was solved to a resolution of 2.4 A with an R factor of 20.6, an Rfree of 28.5, and good stereochemistry. This result could lead to a clinically useful product based on antibody C219 for the diagnosis of P-glycoprotein-mediated multidrug resistance. The molecule will also be useful in biophysical studies of functional domains of P-glycoprotein, as well as studies of the intact molecule.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Crystallographic observation of a covalent catalytic intermediate in a beta-glycosidase.

The three-dimensional structure of a catalytically competent glycosyl-enzyme intermediate of a retaining beta-1,4-glycanase has been determined at a resolution of 1.8 A by X-ray diffraction. A fluorinated slow substrate forms an alpha-D-glycopyranosyl linkage to one of the two invariant carboxylates, Glu 233, as supported in solution by 19F-NMR studies. The resulting ester linkage is coplanar with the cyclic oxygen of the proximal saccharide and is inferred to form a strong hydrogen bond with the 2-hydroxyl of that saccharide unit in natural substrates. The active-site architecture of this covalent intermediate gives insights into both the classical double-displacement catalytic mechanism and the basis for the enzyme's specificity.

Binding Sites↗
PubMed1994

Structural and kinetic characterization of a beta-lactamase-inhibitor protein.

The past decade has seen an alarming worldwide increase in resistance to beta-lactam antibiotics among many pathogenic bacteria, which is due mainly to plasmid- or chromosomally encoded beta-lactamases that specifically cleave penicillin and cephalosporins, rendering them inactive. There is therefore a need to develop new strategies in the design of effective inhibitors of beta-lactamase. All the small-molecule inhibitors in clinical use are not very effective and are rapidly degraded. Furthermore, newly characterized mutants of the plasmid-mediated beta-lactamase TEM-1 are highly resistant to these small-molecule inhibitors, including clavulanic acid and tazobactam. It has been shown that Streptomyces clavuligerus produces an exocellular beta-lactamase inhibitory protein (BLIP; M(r) 17.5 K). Here we present data defining BLIP as the most effective known inhibitor of a variety of beta-lactamases, with Ki values in the subnanomolar to picomolar range. To identify those features in BLIP that make it such a potent inhibitor, we have determined its molecular structure at 2.1 A resolution. BLIP is a relatively flat molecule with a unique fold, comprising a tandem repeat of a 76-amino-acid domain. Each domain consists of a helix-loop-helix motif that packs against a four-stranded antiparallel beta-sheet (Fig. 1a). To our knowledge, BLIP is the first example of a protein inhibitor having two similarly folded domains that interact with and inhibit a single target enzyme.

Amino Acid Sequence↗
PubMed1992

Molecular structure of the acyl-enzyme intermediate in beta-lactam hydrolysis at 1.7 A resolution.

The X-ray crystal structure of the molecular complex of penicillin G with a deacylation-defective mutant of the RTEM-1 beta-lactamase from Escherichia coli shows how these antibiotics are recognized and destroyed. Penicillin G is covalently bound to Ser 70 0 gamma as an acyl-enzyme intermediate. The deduced catalytic mechanism uses Ser 70 0 gamma as the attacking nucleophile during acylation. Lys 73 N zeta acts as a general base in abstracting a proton from Ser 70 and transferring it to the thiazolidine ring nitrogen atom via Ser 130 0 gamma. Deacylation is accomplished by nucleophilic attack on the penicilloyl carbonyl carbon by a water molecule assisted by the general base, Glu 166.

Acylation↗