PubMed Health⌕ Search

Biomedical subjects

R E McDonald

Publications and source records attributed to R E McDonald.

At least 19 recordsLinked to original sources
PubMed1992

Quantitative fluorometric analysis of plant and microbial chitosanases.

A quantitative fluorometric assay for chitosanase activity in bacterial and plant tissues was developed. The assay can be conducted with either finely milled preparations of chitosan in suspension or dissolved chitosan; activity is based on measurements of glucosamine (GlcN) or oligomers of GlcN. GlcN is detected fluorometrically after reaction with fluorescamine with detection in the nanomole range. Fluorescence measurements of chitosanase activity and radioassay of chitinase in commercial preparations of chitinase from Streptomyces griseus revealed that both activities were present. Specific activities for the S. griseus chitosanase using suspended and soluble chitosans were respectively 1.24 and 6.4 mumol GlcN.min-1.mg protein-1. Specific activity of the S. griseus chitinase was 0.98 mumol GlcN.min-1.mg protein-1. Sweet orange callus tissue was tested for chitosanase and chitinase activity. It was necessary to remove small amine-containing molecules from the callus preparations before chitosanase activity could be assayed. The specific activity for chitinase and chitosanase in desalted extracts of nonembryogenic Valencia sweet orange callus tissue was determined to be 18.6 and 89.4 nmol GlcN.min-1.mg protein-1, respectively.

Chitin↗
PubMed1991

Identification of minor C18 triene and conjugated diene isomers in hydrogenated soybean oil and margarine by GC-MI-FT-IR spectroscopy.

Vegetable oils are partially hydrogenated in order to produce palatable products of suitable plasticity. The constituents of these new dietary products are complex mixtures of fatty acid isomers with different nutritional properties. A rapid method is described for separating and identifying fatty acid methyl ester (FAME) isomers of linolenic (octadecatrienoic, 18:3) acid and of conjugated octadecadienoic (18:2) acid, minor species found in hydrogenated soybean oil and margarine, by capillary gas chromatography-matrix isolation-Fourier transform-infrared (GC-MI-FT-IR) spectroscopy. FAMEs of 18:3 acid isomers in margarine, soybean oil hydrogenated in our laboratory, and isomerized linolenic acid were identified by this method, and MI-FT-IR spectra of FAME geometric isomers of octadecatrienoic and conjugated octadecadienoic acids are reported for the first time. Five major C18 triene GC peaks are found in chromatograms of isomerized methyl linolenate, representing species with tri-cis and tri-trans configurations and three species with cis-trans mixed configurations. FAME isomers with these configurations are also found for a hydrogenated soybean oil having an iodine value of 111. Methyl linolenate (tri-cis) is no longer found when soybean oil is further hydrogenated to an iodine value of 96. IR spectra characteristic of a tri-trans isomer are obtained for two test samples with iodine values of 111 and 96. Besides methyl linolenate, only isomers with a mono-trans di-cis configuration are found for the margarine analyzed. Conjugated cis-trans and trans-trans 18:2 FAME isomers are also found in all the hydrogenated soybean oil and margarine analyzed.

Chromatography, Gas↗
PubMed1985

Use and application of structural models in dental education research.

The notion of prediction implies causation. Path and structural models explore the causal links rather than mere empirical relationships between variables. This technique involves a breakdown of correlations; it differs from correlation and regression methods in that it provides relevant information in the presence of important but unobserved (latent) explanatory variables and of measurement errors in the data. It also allows for more than one regression analysis simultaneously and affords inference through tests of the model. In this study, latent abilities of dental students were analyzed as causes and professional achievements as effects, with preadmission performances as indicators of latent abilities. A model with three constructs is consistent with the observed data. The results demonstrate that whereas correlation analysis presents limitations in interpretation, structural analysis focuses clearly on the direct impact of the quality of dental school education, rather than preadmission background, on clinical performance and board success as measures of future professional performance.

Aptitude↗
PubMed1983

Paratesticular mesotheliomas.

Paratesticular mesotheliomas are uncommon tumors. We report 2 such cases and discuss their clinical and pathological findings.

Adult↗
PubMed1982

Professional performance among dental students: a factor analysis.

This study uses factor analysis of dental school performance to extract the underlying factors that are inherent in a set of a student's grades and to evaluate whether a given grade may be associated with more than one factor. Results suggest that overall performance is associated with factors that may be identified as basic science, dental science, and manual skill. The dental science factor appears to be developed during professional training and tends to be less clearly defined that the basic science and manual skills factors, respectively, the associations of clinical course grades with the defined factors are generally low, reflecting the complex involvement of dental clinic performance. It is reasonable to speculate, therefore, that dental school grades, when compounded together as overall GPA across the basic abilities of the students, constitute a likely source of variation that accounts for difficulties in prediction studies when they are used as criterion variables.

Clinical Competence↗
PubMed1982

A derived basic ability criterion for predicting dental students' performance.

This study represents an attempt to develop a valid criterion for predicting students' performance while in dental school. Dental students' overall grade point averages were partitioned into component measures of relevant basic ability clusters in terms of factor scores. The derived indices were used as criterion variables in simple and multiple correlation and regression analyses, with Dental Admission Test (DAT) and predental college scores as predictors. Results showed that basic science abilities were associated with the preprofessional academic predictors, and manual skills with the DAT Perceptual Motor Ability Test (PMAT) scores. None of the presently available preprofessional predictors, taken singly or together, were correlated sufficiently with the factor-associated dental science performance or the nonfactor-associated dental clinical performance for effective prediction. Findings that the development of dental and clinical proficiency at the predoctoral level depends neither on available predictors nor on preprofessional background in the basic sciences have implications for traditional admission policies.

Clinical Competence↗
PubMed1980

Activities by the schools to improve the distribution of dentists: an AADS report.

It appears that most dental schools have not yet become actively involved in efforts to solve maldistribution problems. However, there seems to be increasing interest in the potential benefits of extramural experience programs. Coordination of efforts by the schools, the state dental associations, and the state boards of dental examiners is very limited, but is clearly needed. Admissions committees seem to be trying to take into account the needs of rural areas and the inner city as well. Finally, the results of the survey point up the need for further study of these problems and of the value of particular approaches to them.

Dentists↗