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G Rhodes

Publications and source records attributed to G Rhodes.

81 records · Page 5Linked to original sources
PubMed1982

Mixture analysis by triple-quadrupole mass spectrometry: metabolic profiling of urinary carboxylic acids.

In this new method for profiling urinary carboxylic acids, lyophilized urine samples are analyzed directly with a triple-quadrupole mass spectrometer. Extraction, derivatization, and lengthy gas-chromatographic separation procedures are obviated by this approach. Total sample-preparation, instrument, and data-analysis time per sample is about 15 min. More than 100 different organic acids can be detected in a typical urine sample. All components of the solid urine residue are volatilized into the ion source of the mass spectrometer and converted to (M-1)- ions by reaction with OH- under chemical ionization conditions. Quadrupole 1 is set to transmit ions of a particular m/z ratio, which in turn collide with molecular nitrogen in quadrupole 2 and dissociate to smaller charged fragments. Carboxylic acid (M-1)- ions uniquely lose either CO2 (44 atomic mass units) or both H2O and CO2 (62 atomic mass units). Quadrupole 3 is set to pass only ions that have lost either 44 or 62 atomic mass units. Accordingly, the instrument specifically detects carboxylic acids in the urine matrix and no other components. Direct analysis of polyethylene glycols and their acidic metabolites in urine and serum of a burn patient treated with an antimicrobial cream having a polyethylene glycol base is also discribed.

Adult↗
PubMed1981

Metabolic abnormalities associated with diabetes mellitus, as investigated by gas chromatography and pattern-recognition analysis of profiles of volatile metabolites.

Patterns of volatile metabolites in urine, as obtained by glass-capillary gas chromatography, were investigated by use of a nonparametric pattern-recognition method, in an effort to detect abnormalities associated with diabetes. We used threshold logic unit analysis on a data set consisting of normal subjects and those with diabetes mellitus, and could predict patterns for volatile metabolites as belonging to the proper class in 94.83% of the cases examined. In addition, a feature-extraction algorithm isolated those volatile constituents that are most useful in making the normal/diabetic classification. We used gas chromatography/mass spectrometry to identify important profile constituents. Finally, these same pattern-recognition methods indicated strong sex-related patterns in these volatiles.

Chromatography, Gas↗
PubMed1979

A simple and rapid purification method for Escherichia coli DNA polymerase I.

We report a simple, three-step method for the purification of Escherichia coli DNA polymerase I. Its advantages over other procedures are ease and rapidity, the absence of an autolysis or any high speed centrifugation step, and applicability to large quantities of material. In addition, RNA polymerase can be isolated as a by-product. We have applied this method to purify DNA polymerase both from wild type E. coli cells and from cells bearing a lambda prophage carrying the polA gene (Kelley, W.S., Chalmers, K., and Murray, N.E. (1977) Proc. Natl. Acad. Sci. U.S.A. 74, 5632-5636). This latter source amplifies the amount of DNA polymerase in the cells by at least 10-fold.

Coliphages↗
PubMed1979

Application of pattern recognition and feature extraction techniques to volatile constituent metabolic profiles obtained by capillary gas chromatography.

The applicability of threshold logic units, a form of nonparametric pattern recognition, to the processing of metabolic profile data obtained by high-efficiency glass capillary column gas chromatography has been investigated. The test data included profiles of the volatile constituents of urine from normal individuals and from individuals with diabetes mellitus. A feature extraction algorithm allowed for dimensionality reduction and indicated the constituents most important in the normal versus pathological distinction. With an optimum number of dimensions, a normal versus pathological prediction rate of 93.75% was achieved. Gas chromatography-mass spectrometry was utilized to identify important profile constituents.

Chromatography, Gas↗
PubMed1975

Kinetic analysis of ribonucleic acid chain initiation by Escherichia coli Ribonucleic acid polymerase bound to DNA.

The kinetics of the RNA chain initiation reaction carried out by RNA polymerase bound to the initiator region of a DNA template have been analyzed. Initiation proceeds in a two-substrate reaction in which the initial binary complex (enzyme-DNA) is transformed into a ternary complex (enzyme-DNA-RNA) by formation of a dinucleoside tetraphosphate and release of inorganic pyrophosphate. In this reaction RNA polymerase serves as a reactant rather than acting catalytically. The concentration of the reacting binary complex decreases throughout the reaction; hence steady state approximations cannot be used. Kinetic equations for an ordered two-substrate reaction are derived. These are most useful for the special case of reaction in the presence of an inhibitor of initiation, such as rifampicin. Equations for the latter instance are solved exactly with recourse to the steady state approximation. It is found that measurements of the extent of the initiation reaction determined at different inhibitor and substrate concentrations can give information about the initiation reaction analogous to that obtained in standard steady state kinetic analysis. This theory is applied to the experimental study of the initiation reaction carried out by Escherichia coli RNA polymerase. It is found that the inhibitor rifampicin, which blocks the initiation reaciton, acts by binding to the same form of the binary complex as the nucleoside triphosphate substrate (ATP or GTP) which is incorporated into the 5' terminus of nascent RNA molecule. The binding of the 5'-terminal nucleoside triphosphate to the enzyme appears to be rate-limiting for the initiation reaction under standard assay conditions. Initiation appears to follow an ordered reaction mechanism; however, the order of addition of the two substrates is still uncertain.

Binding Sites↗
PubMedDate not supplied

The rapid diagnosis of infectious mononucleosis using an ELISA that detects IgM antibody to a peptide component of Epstein-Barr virus nuclear antigen.

An enzyme-linked immunosorbent assay (ELISA) that detects IgM antibody to a peptide component of the Epstein-Barr virus (EBV) nuclear antigen (EBNA-1) was compared with a conventional rapid heterophil antibody method for the rapid diagnosis of infectious mononucleosis. Discrepancies between the two methods were further analyzed using an indirect immunofluorescence assay to detect antibodies to EBV antigens. We evaluated 298 cases of suspected infectious mononucleosis. The ELISA was very sensitive (98.7%) and able to detect some cases (seven (9%) of 75 confirmed positives) that were negative by the rapid heterophil antibody test, but confirmed by immunofluorescence. However, approximately 17% of all positive tests could not be confirmed by EBV-specific immunofluorescence; thus, the overall positive predictive value was 83%; negative predictive value was 99.5%; and specificity was 93%. The high rate of false-positive tests makes this rapid ELISA unsuitable for the diagnosis of infectious mononucleosis.

Adolescent↗
PubMedDate not supplied

The application of toxicokinetic data to dosage selection in toxicology studies.

Appropriate dosage selection is a key element in the design of toxicology studies and, hence, is the first step in the process of evaluating the safety of a new chemical or pharmaceutical agent. This demands careful consideration of exposure to the drug or chemical under investigation in relation to the pharmacological or toxicological effects it evokes in an experimental animal. Toxicokinetic data provide this perspective, but they should not be considered exclusively of other data which reflect the specific activity, potency, or metabolism of the drug or chemical in each individual test species. It is equally inappropriate to base dosage selection in toxicology studies exclusively on functional or morphological endpoints that cause effects outside the range which can be accommodated by homeostatic mechanisms and repair processes. Finally, extrapolation of toxicokinetic data across species lines can lead to serious miscalculations with respect to both dosage selection and the process of risk assessment. In each case, decisions should be based on the integration of toxicokinetic data with other measures and endpoints of biological and toxicological effect.

Animals↗
PubMedDate not supplied

Computer graphics and developmental theory: a powerful partnership.

Educating student nurses to successfully use computer technology involves conscientious planning from nursing faculty responsible for curriculum integration. Many computer elements may be considered such as computer literacy, word processing, and computer assisted instruction. Database programs, spreadsheet applications, and statistical packages are also often incorporated into curriculum integration efforts. Computer graphics and desk-top publishing can also be used as an effective teaching strategy. The following describes an attempt to combine a creative teaching approach for developmental theory within a course on human development while expanding on students' computer skills in the field of computer graphics.

Computer Graphics↗