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D J Newman

Publications and source records attributed to D J Newman.

At least 91 records · Page 5Linked to original sources
PubMed1991

Stabilization of turbidimetric immunoassay by covalent coupling of antibody to latex particles.

Turbidimetric immunoassay is commonly used to quantify serum proteins. Latex-particle enhancement of this type of assay has been primarily associated with increasing assay sensitivity. However, covalent coupling of an antibody to a latex particle can offer other advantages that are also pertinent in measurement of high concentrations of analytes. By using a common antibody with IgG as a model analyte, we describe the development of a nonenhanced and a latex-particle-enhanced turbidimetric assay for measuring serum IgG. Both assays show adequate analytical recovery and parallelism, and results compare well with those by rate nephelometry. The latex-enhanced assay has equivalent sensitivity, working range, and interassay precision, but much greater signal change and calibration stability than the nonenhanced assay. In addition, with latex particles, less antiserum is needed. Coupling antibodies to latex particles offers considerable advantages, even when an improved assay detection limit is not required.

Humans↗
PubMed1991

Particle-enhanced turbidimetric immunoassay of sex-hormone-binding globulin in serum.

A particle-enhanced turbidimetric immunoassay (PETIA) for human sex-hormone-binding globulin (SHBG) is described. The method involves use of antibody covalently coupled to latex particles and is almost fully automated, with sample processing being complete in less than 20 min. The working reagents are stable for at least three months, and full calibration of the assay each day is not essential. A particular advantage is that pretreatment of samples is rarely required because the working range of the assay is from 2.0 to 320 nmol/L for nondiluted serum. Intra- and interassay CVs were less than 4.5% and 8.5%, respectively, and mean analytical recovery was 101.5%. SHBG concentrations of 129 serum samples determined by this method and by a commercially available immunoradiometric assay correlated highly.

Female↗
PubMed1990

A rapid and robust particle-enhanced turbidimetric immunoassay for serum beta 2 microglobulin.

A rapid particle-enhanced turbidimetric immunoassay (PETIA), for the measurement of serum beta 2-microglobulin is described. The method has a working range of 0.2-40 mg/l, with good precision and a correlation coefficient of 0.97 when compared with an established radioimmunoassay method. One of the major advantages of this assay is the stability of the calibration curve (up to at least 20 months). This, and the fact that no pretreatment of serum samples is necessary, makes the assay ideally suited for all types of routine determination.

Animals↗
PubMed1990

Rapid, robust method for measuring low concentrations of albumin in urine.

We describe a rapid particle-enhanced turbidimetric immunoassay for albumin in urine. Intra- and interassay CVs were less than 5% and less than 10%, respectively, the detection limit is 2 mg/L, and the working range extends to 200 mg/L. Mean analytical recovery of albumin added to centrifuged urines was 100% (SD 10.6%), and, when results were compared with those by the Pharmacia RIA, the correlation coefficient was 0.99. The working reagents are stable for at least six months; thus this assay is suited for both batch and urgent analysis.

Albuminuria↗
PubMed1990

Dual-task performance on an interactive human/computer space shuttle flight experiment.

INTRODUCTION: This paper details ground-based results of the Mental Workload and Performance Experiment (MWPE) which examines human performance for cognitive decision-making and eye-hand-coordinated motor tasks. MWPE is manifest on the International Microgravity Laboratory (IML-1) Space Shuttle Mission and is scheduled to fly in December of 1990. The MWPE protocol combines a Sternberg memory search with a Fitts' target acquisition resulting in a "Fittsberg" dual-task paradigm. The purpose of this study was to evaluate the serial execution theory underlying the Fittsberg dual-task paradigm. METHODS: A total of nineteen subjects performed two experimental test batteries. Unusual body dynamics were imposed on subjects in order to assess altered environment performance. In the first test battery, subjects performed experiments in either the upright postural orientation or the supine (recumbent) postural orientation. During the second test battery, an altered environment was electronically created by introducing a first-order lag characteristic between the graphic input device and the computer. Performance and workload were evaluated by reaction time, movement time, and subjective rating measurements for the dual-task paradigm. RESULTS: The major contributors to reaction and movement times are as predicted by Sternberg and Fitts, however, there are many other influences not accounted for by the classical models. For MWPE, interdependence among the memory set size and index of difficulty experimental variables is in conflict with the serial execution assumption of the Fittsberg dual-task paradigm. CONCLUSIONS: When interaction among variables exists, the dual-task paradigm can not simply be modeled as a Sternberg memory task plus a Fitts target acquisition, rather, new performance metrics for the memory search and target acquisition tasks require that all the significant variables in the MWPE protocol be modeled. The interdependence among variables hints that the operator incorporates some degree of parallel processing rather than exclusively performing in a serial manner.

Humans↗
PubMed1989

Is intact PTH a sensitive biochemical indicator of deranged calcium homeostasis in vitamin D deficiency?

Intact PTH was elevated in 38/40 Asians with reduced serum 25 hydroxyvitamin D [25(OH)D] including seven patients with normal serum calcium, phosphate and alkaline phosphatase. Changes in intact PTH were disproportionately greater than for other biochemical parameters, making it the most sensitive early indicator of deranged calcium homeostasis in vitamin D deficiency.

Ascorbic Acid Deficiency↗
PubMed1988

Clinical and laboratory evaluation of a two-site immunoradiometric assay for intact parathyroid hormone.

The analytical performance and clinical utility of a direct immunoradiometric assay (IRMA) for intact 1-84 human parathyroid hormone (PTH) was evaluated. The assay is available commercially (Allégro intact PTH, Nichols Institute) and utilises two affinity purified region-specific antisera against either 1-34 (radiolabelled antibody) or 39-84 (solid phase antibody) human PTH. High assay sensitivity (detection limit, 1.4 pg 1-84 PTH/mL) permitted the measurement of PTH in all normocalcaemic individuals studied. Elevated results were obtained in all patients (21 studied) with histologically proven primary hyperparathyroidism (PHPT) and 34 out of 35 patients with presumptive PHPT. Thirteen out of 24 patients with non-parathyroid hypercalcaemia had suppressed results, but the remainder had concentrations within the reference range.

Adult↗
PubMed1986

Studies on the active site of succinyl-CoA:tetrahydrodipicolinate N-succinyltransferase. Characterization using analogs of tetrahydrodipicolinate.

Cyclic and acyclic analogs of tetrahydrodipicolinate (THDPA) are evaluated in a study of the active site of succinyl-CoA:tetrahydrodipicolinate N-succinyltransferase. In addition to the natural substrate, THDPA, one cyclic and several acyclic compounds are also succinylated. 2-Hydroxytetrahydropyran-2,6-dicarboxylic acid is a potent competitive inhibitor having a Kis of 58 nM. Based on the results of this study, a stereochemical model for the succinylation of THDPA is proposed. The major features of this model are as follows. 1) The succinylase binds THDPA (L-configuration). 2) Hydration of the imine group follows to give 2-hydroxypiperidine-2,6-dicarboxylic acid in which the two carboxyl groups are trans. 3) Succinylation then occurs and the ring opens to give the acyclic product. It is suggested that 2-hydroxytetrahydropyran-2,6-dicarboxylic acid is a transition state analog by virtue of the fact that it structurally resembles the hydrated intermediate.

Acyl Coenzyme A↗
PubMed1986

Peptides of 2-aminopimelic acid: antibacterial agents that inhibit diaminopimelic acid biosynthesis.

Succinyl-CoA:tetrahydrodipicolinate-N-succinyltransferase is a key enzyme in the biosynthesis of diaminopimelic acid (DAP), a component of the cell wall peptidoglycan of nearly all bacteria. This enzyme converts the cyclic precursor tetrahydrodipicolinic acid (THDPA) to a succinylated acyclic product. L-2-Aminopimelic acid (L-1), an acyclic analogue of THDPA, was found to be a good substrate for this enzyme and was shown to cause a buildup of THDPA in a cell-free enzyme system but was devoid of antibacterial activity. Incorporation of 1 into a di- or tripeptide yielded derivatives that exhibited antibacterial activity against a range of Gram-negative organisms. Of the five peptide derivatives tested, (L-2-aminopimelyl)-L-alanine (6) was the most potent. These peptides were shown to inhibit DAP production in intact resting cells. High levels (30 mM) of 2-aminopimelic acid were achieved in the cytoplasm of bacteria as a result of efficient uptake of the peptide derivatives through specific peptide transport systems followed, presumably, by cleavage by intracellular peptidases. Finally, the antibacterial activity of these peptides could be reversed by DAP or a DAP-containing peptide. These results demonstrate that the peptides containing L-2-aminopimelic acid exert their antibacterial action by inhibition of diaminopimelic acid biosynthesis.

Acyltransferases↗
PubMed1986

Glycopeptide antibiotics: a mechanism-based screen employing a bacterial cell wall receptor mimetic.

The evolution of a highly targeted screening program for the discovery of antibiotics of the glycopeptide (vancomycin) class is described. A holistic approach was utilized which optimized not just screening techniques but also the selection of candidate producer cultures and their growth under conditions which enhanced production of target compounds. Two screen techniques were utilized; differential inhibition of a vancomycin-resistant strain and its susceptible parent, and a specific antagonism screen using the reversal of glycopeptide activity by a tripeptide analog of the glycopeptide receptor, diacetyl-L-lysyl-D-alanyl-D-alanine. The latter screen was 2- to 32-fold more sensitive to known glycopeptides than the former, and was absolutely specific, yielding no false positive responses. The use of the tripeptide antagonism assay, combined with optimized culture selection and growth conditions yielded novel glycopeptide antibiotics at a rate of 1 per 320 cultures screened. With a holistic approach to screening and properly optimized techniques, large numbers of cultures do not need to be examined in order to discover novel antibiotics.

Actinomycetales↗
PubMed1985

Relative rates of transport of peptidyl drugs by Candida albicans.

A variety of peptide drugs are known to be active against Candida albicans; however, little is known about the transport of such agents into the target organism. To provide further information concerning transport of this type, we studied the uptake of two classes of small linear peptides: polyoxins which act intact within the cell and the m-fluorophenylalanyl (m-F-Phe) peptides which require peptidase cleavage to release m-F-Phe. Competition studies with a specific dipeptide detector (alanyl-alpha-thiophenylglycine) enabled us to determine Ki values of 2.6 microM for nikkomycin Z and 350 microM for polyoxin D. Rates of uptake of the peptidyl-nucleosides are approximately 30 times lower than those of the m-F-Phe peptides (apparent maximal velocities: nikkomycin Z, 62 pmol min-1 mg (dry weight) of cells-1; M-F-Phe alanine 1.3 nmol min-1 mg (dry weight) of cells-1). For both the m-F-Phe peptides and the peptidyl-nucleosides, the affinity of the drug for the transport system is an important determinant of its whole-cell activity.

Antifungal Agents↗
PubMed1984

Affinity of cefonicid, a long-acting cephalosporin, for the penicillin-binding proteins of Escherichia coli K-12.

The binding of cefonicid (SK&F 75073), a new parenteral cephalosporin, to the penicillin-binding proteins (PBPs) of Escherichia coli K-12 (strain KN-126) was determined by competitive binding studies versus benzyl[14C]penicillin. Cefonicid showed its greatest affinity for PBPs 1a greater than 3 greater than 1b, bound with low affinity to PBPs 4 greater than 2, and did not bind to PBPs 5 and 6. Provisional affinity constants (cefonicid concentration that gave 50% inhibition of [14C]penicillin binding) were determined: PBP 1a, less than 0.25 microgram/ml; PBP 3, 0.7 microgram/ml; PBP 1b, 10 micrograms/ml; PBP 4, 26 micrograms/ml; PBP 2, 90 micrograms/ml; PBPs 5 and 6 greater than 256 micrograms/ml. Direct binding studies with [14C]-cefonicid confirmed this pattern of binding. Subinhibitory concentrations of cefonicid (MIC, broth 0.2 microgram/ml, agar 0.4 microgram/ml) induced filamentation of E. coli KN-126. This implies that PBP 3 is the primary inhibitory site despite the higher affinity of PBP 1a for this cephalosporin.

Bacterial Proteins↗
PubMed1981

Cefonicid: a stable beta-lactamase inhibitor.

The stability of cefonicid (SK&F 75073) towards representatives of six major classes of beta-lactamases was determined using a spectrophotometric assay. Cefonicid was stable to hydrolysis by the Type I enzyme from Enterobacter cloacae and by the enzyme from the anaerobe, Bacteroides fragilis. It was 6 to 7 times more stable than cefamandole to the Type IIIA and B enzymes from Escherichia coli, a little less stable than this antibiotic to the Type V enzyme from E. coli, and of equal stability to the Type IV enzyme from Klebsiella aerogenes. Cefonicid was a non-competitive inhibitor (Ki of 0.8 x 10(-6)M) of cephalothin hydrolysis by the Type I enzyme.

Cefamandole↗