Biomedical subjects

G D Hunter

Publications and source records attributed to G D Hunter.

At least 19 recordsLinked to original sources

PubMed1992

Expression of a bacterial aspartase gene in Aspergillus nidulans: an efficient system for selecting multicopy transformants.

The Escherichia coli aspartase gene aspA has been expressed in the fungus Aspergillus nidulans using the powerful constitutive gpdA promoter and trpC terminator, both from A. nidulans. Multiple, but not single, copies of aspA overcome nutritional deficiencies resulting from the loss of catabolic NAD-linked glutamate dehydrogenase. They also circumvent certain nutritional deficiencies resulting from loss of the positive-acting regulatory gene product mediating nitrogen metabolite repression. Both of these cases of physiological suppression involve the aspartase-catalyzed catabolism of aspartate to ammonium plus fumarate. No physiological evidence for the opposite reaction leading to aspartate synthesis was obtained as multiple copies of aspA did not affect the phenotype resulting from the loss of anabolic NADP-linked glutamate dehydrogenase. The use of vectors containing aspA and recipients lacking NAD-linked glutamate dehydrogenase is an efficient means of selecting multicopy transformants in A. nidulans and also offers the possibility to select strains having increased aspartase levels from original transformants.

Aspartate Ammonia-Lyase↗

PubMed1985

Ganglioside patterns during cerebral development in the normal and reeler mouse.

Gangliosides were extracted from cerebral tissue of reeler and normal mice, and analyzed by two-dimensional thin-layer chromatography at embryonic and postnatal ages. The ganglioside pattern changed substantially as development proceeded in the telencephalon of both reeler and normal mice, but was the same at any given age for both conditions, despite the marked histological differences between reeler and normal samples. These results indicate that abnormal ganglioside patterns do not result from the reeler mutation at early stages of brain development, and that the cell misalignment characteristic of the reeler phenotype involves molecules other than gangliosides.

Animals↗

PubMed1982

Catecholamine metabolism in brain slices. Determination of relevant precursor pool and the effects of elevated K+.

Catecholamine synthesis from [3H]tyrosine was studied in slices of striatum, cerebellum and substantia nigra of mice. If low concentrations of tyrosine (less than 5.5 microM) were added to the incubation medium, the slices released significant amounts of tyrosine into the medium during the incubation. Kinetic analysis of the same experiments indicated that medium tyrosine and not tissue tyrosine was the appropriate precursor for both dopamine (DA) synthesis and protein synthesis in striatal slice. Concentrations of medium tyrosine of 8.25 microM or greater were sufficient to prevent changes of medium tyrosine during incubation and thus maintained a constant specific activity of precursor. Increasing concentrations of medium K+ increased both the accumulation of [3H]DA and its release from striatal slices. However, accumulation was stimulated at a concentration of K+ (14 mM) that had no significant stimulatory effect on release, suggesting that the stimulatory effects of K+ on synthesis and release are mediated by separate processes. Release of 14CO2 from [1-14C]tyrosine closely paralleled the accumulation of [3H]DA from [3H]tyrosine. Release of preloaded [14C]DA closely paralleled that of [3H]DA synthesized from [3H]tyrosine, suggesting a common functional pool. The principal DA catabolite produced was dihydroxyphenylacetic acid (DOPAC). The appearance of labeled DOPAC in the media was greatly enhanced by K+ stimulation.

Animals↗

PubMed1981

Interspecies comparison of brain ganglioside patterns studied by two-dimensional thin-layer chromatography.

Brain gangliosides from four vertebrate classes (fish, amphibia, aves, and mammalia) were studied by patterns generated with the use of two-dimensional thin-layer chromatography. In an effort to retain possible alkalilabile gangliosides, samples were not base-hydrolyzed. Resultant chromatograms revealed complex patterns of the major known gangliosides and a number of minor and trace molecular species previously unresolved. More than 30 resorcinol-positive components were detected in mammalian neural samples. Our data indicate both qualitative and quantitative differences in the chromatogram patterns between the vertebrate classes, but potentially greater qualitative similarity exists between the lower and higher classes than has previously been noted.

Animals↗

PubMed1976

Changes in a protein-nucleic acid complex from synaptic plasma membrane of scrapie-infected mouse brain.

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Animals↗

PubMed1976

Search for scrapie-specific RNA and attempts to detect an infectious DNA or RNA.

Preparations of in vivo labelled RNA from normal and scrapie infected mouse brains were fractionated by polyacrylamide gel electrophoresis. No appreciable differences were detected between the two preparations. The biological activity of preparations of RNA and DNA from scrapie brain was also examined. In each case the nucleic acid was obtained by one method envolving the use of phenol and one without phenol. Attempts were made to bind the nucleic acid to normal membrane by three different methods. In no instance was a single case of scrapie obtained by inoculating nucleic acid extracts from scrapie brain either alone or associated with normal membranes. It is concluded that a putative scrapie-specific nucleic acid must either be present in scrapie brain in such an unusual from that it is not extracted readily by methods suitable for the preparation of most virus nucleic acids; or, if it is extracted, that it has no detectable biological activity. In either case, the scrapie agent differs substantially in its properties from the plant viroids.

Animals↗

PubMed1976