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Biomedical subjects

M A Thomas

Publications and source records attributed to M A Thomas.

At least 145 records · Page 8Linked to original sources
PubMed1983

Study of the Hansenula anomala yeast flavocytochrome-b2--cytochrome-c complex 1. Characterization of fluorescent Zn(II)-substituted cytochrome c.

Substitution of Fe2+ for the Zn2+ ion in Hansenula anomala cytochrome c provides a luminescent derivative suitable as a probe for the determination of the interaction of cytochrome c with H. anomala flavocytochrome b2; its light absorption and fluorescence properties have been characterized. H. anomala Zn-cytochrome c appears to be in the form of a stable though non-covalent dimer from molecular weight determinations performed using gel filtration, polyacrylamide gel electrophoresis under denaturing conditions, and ultracentrifugation methods. By contrast, metal-free porphyrin-cytochrome c, the precursor of Zn-cytochrome c obtained upon removal of iron from cytochrome c in cold anhydrous fluorhydric acid, had the same partition coefficient as native cytochrome c through conventional gel filtration. Significant conformational perturbations of H. anomala cytochrome c should therefore follow from Zn2+ incorporation into the porphyrin c moiety. Titrations at low ionic strength with native, tetrameric H. anomala flavocytochrome b2 in the lactate-reduced state showed a simple binding equilibrium (Kd = 0.1 microM at I = 0.03 M, 10 degrees C) with a stoichiometry of one Zn-cytochrome c dimer per protomer of flavocytochrome b2. Quenching of the Zn-porphyrin c fluorescence within this complex was much larger (43%) than reported by other authors using cytochrome c and flavocytochrome b2 from different sources.

Ascomycota↗
PubMed1983

Study of the Hansenula anomala yeast flavocytochrome-b2-cytochrome-c complex 2. Localization of the main association area.

The reversible association of the Zn2+-substituted Hansenula anomala cytochrome c dimer (Thomas et al., preceding paper in this issue) to flavocytochrome b2 in oxidized or lactate-reduced state has been investigated by fluorimetry. The same method has been used for the determination of Zn-cytochrome c complexing to defined proteolytic fragments of flavocytochrome b2, either heme-b2-containing monomers or a flavin-linked tetramer. All these fragments but the isolated cytochrome b2 core showed binding stoichiometries, Kd values and ionic strength dependences quite similar to those found for native flavocytochrome b2. These data allowed localization of the single high-affinity binding site of cytochrome c on a particular globule in the dehydrogenase domain of the flavocytochrome b2 protomers. Quenching of the Zn-porphyrin c fluorescence in the various complexes occurred with only minor changes of the fluorescence lifetime and did not show any direct relationship to the presence or the redox state of the heme b2 group.

Ascomycota↗
PubMed1982

Envenomation by a King Island tiger snake (Notechis ater humphreysi).

A venomous King Island tiger snake (Notechis ater humphreysi)bit a herpetologist on the hand on the forty-eight floor of a Sydney city building. Prompt first-aid treatment, comprising the application of a wide constrictive bandage the length of the limb, combined with immobilisation, delayed central movement of the venom until resuscitative care and antivenom were available. The patient had received tiger-snake antivenom 16 years previously, and also suffered from atopic eczema. Administration of 6000 units of tiger-snake antivenom after parenteral administration of an antihistamine was uneventful. A transient rash on the second day and a mild urticarial rash on the twelfth day after envenomation may have been either serum reactions or allergic response to other medication.

Adult↗
PubMed1981

Tritiated thymidine incorporation does not measure DNA synthesis in ribavirin-treated human cells.

When the incorporation of tritiated thymidine into acid insoluble material was measured, ribavirin appeared to be a potent inhibitor of DNA synthesis in KB cells and human lymphocytes. Inhibition was nearly 100-fold less, however, when DNA synthesis was measured by incorporation of phosphorus-32-labeled phosphate or by DNA fluorescence. The potent inhibition detected by incorporation of tritiated thymidine into DNA actually was the result of a potent effect on the labeling of deoxythymidine triphosphate, not on the synthesis of DNA.

Cells, Cultured↗
PubMed1981

Heterogeneity of rat peritoneal and alveolar macrophage populations: characterization of their surface antigens by antisera.

Antisera were raised in rabbits against rat peritoneal and alveolar macrophages and against rat thymocytes. In vitro investigations of these antisera using dye-exclusion tests and cytotoxicity and immunofluorescence methods indicated that the immunizing cell types exhibited shared and specific antigens. Extensive absorption studies confirmed these findings, and showed some specificity of the anti-peritoneal serum for peritoneal macrophages and of the anti-alveolar serum for alveolar cells.

Animals↗
PubMed1979

Trichuriasis. Roentgenographic features and differential diagnosis with lymphoid hyperplasia.

Twenty patients with massive trichuriasis were studied with double contrast barium enema. The following changes were observed: 1) Impregnation defects of the colonic wall probably due to abundant mucous secretions. 2) Granular features. 3) Pear-shaped caecum. 4) Radiolucid ringlike images with some contrast material in its center, similar to those seen in lymphoid hyperplasia. On closer observation it was seen that the radiolucid ring was not complete and was continued by a prolongation which corresponds to the whipworm. This feature is central to the differential diagnosis.

Cecum↗
PubMed1977

Adenosine phosphorylase activity in a mutant HEp-2 cell line contaminated with Mycoplasm hyorhinis.

Metabolic studies in HEp-2/MP,MIR cells (an adenosine kinase, hypoxanthine phosphoribosyltransferase negative mutant) indicated the presence of adenosine phosphorylase activity. This activity, unknown in established mammalian cell lines, resulted in the glycosidic cleavage of both adenosine and the antiviral drug arabinosyladenine. The activity was observed readily in the presence or absence of the adenosine deaminase inhibitor conformycin. Isopycnic separation of [3H] thymidine-labeled DNA species in CsCl density gradients resulted in the appearance of two distinct peaks. The heavier peak coincided with [14C]thymidine-labeled marker DNA of human origin, whereas the lighter peak was within the range associated with mycoplasmal DNA. Testing by commercial laboratories confirmed the presence of mycoplasma in HEp-2/MP,MIR cells. The contaminant was identified as Mycoplasma hyorhinis, a porcine mycoplasma. Following gamma-irradiation (3000 rads) to block cellular mitosis, the mucoplasma-contaminated HEp-2/MP,MIR cells were cocultivated with mycoplasma-free wild-type HEp-2 cells which did not exhibit adenosine phosphorylase activity. Following serial cocultivation in a medium designed to favor the survival of the wild-type cells, adenosine phosphorylase activity was found in the previously uninfected cells. Studies of this nature emphasize the need for investigators to carefully monitor their cell lines for mycoplasma.

Adenosine↗
PubMed1977

Reduction in peripheral blood K cells and activated T cells in primary biliary cirrhosis.

Lymphocyte subpopulations were measured in the peripheral blood of 13 patients with primary biliary cirrhosis (PBC), 13 with chronic active hepatitis (CAH), and 16 age- and sex-matched normal subjects. A significant, relative and absolute, reduction in activated T cells and K cells, compared with that in normal subjects, was found in PBC but not in CAH. The reduction in K cells observed in PBC was found to be accompanied by a parallel decrease in lymphocyte-mediated antibody-dependent cytotoxicity.

Adult↗