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Biomedical subjects

B Chance

Publications and source records attributed to B Chance.

At least 505 records · Page 28Linked to original sources
PubMed1975

Carbon monoxide-induced localized toxic anoxia in the rat brain cortex.

A new method has been developed for the determination of maximal reduction of NAD in the rat cerebral cortex. NADH fluorescence (450 nm) induced by 366-nm light and UV reflectance were measured by a time-sharing light pipe fluorometer. The redox state of the cortical surface was altered by perfusion of oxygen or carbon monoxide through a Teflon chamber adjacent to the dura. This study examines changes caused by local perfusion with the two gases in normoxia, hypoxia, and anoxia. Alternation of topical carbon monoxide and oxygen becomes effective in altering the intracellular redox state at 15% inspired oxygen and caused 20% changes at zero inspired oxygen. Conversely, topical application of oxygen to the systemically anoxic tissue causes oxidation of reduced NAPH in the cells within the field of fluorometric observation equivalent to that caused by breathing approximately 8% oxygen systemically.

Animals↗
PubMed1975

H2O2 release from human granulocytes during phagocytosis. I. Documentation, quantitation, and some regulating factors.

The extinction of fluorescence of scopoletin during its oxidation by horseradish peroxidase (HPO) provides a highly sensitive and specific assay for small quantities of peroxide in solution. With this assay, the release of free H2O2 into the extracellular medium by phagocytizing human granulocytes has been documented and quantitated, and some of the regulating factors have been determined. Under basal conditions granulocytes released less than 0.01 nmol/ml of H2O2 (2.5 X 10-6 polymorphonuclear leukocytes/ml). Upon the addition of phagocyte particles (latex, opsonized yeast, or staphylococci), an abrupt increase in extracellular peroxide concentration was observed (greater than 50-fold above basal levels) after latencies as short as 10 s. Release reflected increased intracellular H2O2 production during phagocytosis in that it paralleled the respiratory burst and was absent when phagocytosis was prevented or when cells from patients with chronic granulomatous disease were utilized. Evidence that scpoletin oxidation occurred predominantly in the extracellular medium was obtained by demonstrating a marked inhibition when HPO was omitted from the reaction mixture or when exogenous catalase was added. Similarly, it was found that exogenous serum also inhibited scopoletin oxidation, apparently because of the presence of competing hydrogen donors. H2O2 formation and release were observed at rates which closely paralleled those of phagocytosis. With O2 consumption as an approximate index of H2O2 formation, the fractions released during maximal rates of particle uptake were calculated as follows: for latex, 15.7%; for staphylococci, 10.3%; and for yeast, 4.9%. It is postulated that release is due to diffusion of free H2O2 from an expanded intracellular pool of this substance that develops during phagocytosis. This poos represents tha net of increased synthesis versus catabolism by various enxymatic pathways for H2O2 disposal within the cells. The close relationship between rates of H2O2 formation and rates of phagocytosis by human granulocytes suggests a role for specialized areas of the cell membrane, involved in particle ingestion, in the trigger mechanism for H2O2 synthesis. The consequences of H2O2 release to other cells or organisms in the immediate environment of phagocytizing granulocytes remain to be determined.

Catalase↗
PubMed1974

The development of cytochromes during the cell cycle of a glucose-repressed fission yeast, Schizosaccharomyces pombe 972h-.

1. Spectrophotometric analysis of intact cells of Schizosaccharomyces pombe, harvested from exponentially growing cultures during the phase of glucose repression, revealed the presence of cytochromes a+a(3), c and at least two species of cytochrome b. 2. An absorption maximum at 554nm at 77 degrees K, previously attributed to cytochrome c(1), has been identified as a b-type cytochrome. 3. CO-difference spectra reveal the presence of cytochromes P-420 and P-450 in addition to cytochrome a(3). 4. The cell cycle was analysed by separation of cells into classes representing successive stages in the cell cycle by isopycnic zonal centrifugation. 5. Cytochromes c(548), b(554) and b(560) each exhibited a single broad maximum of synthesis during the cell cycle. 6. Amounts of cytochromes a+a(3) and b(563) (tentatively identified as cytochrome b(T) by its reaction on pulsing anaerobic cell suspensions with O(2)) oscillated in phase, and showed two maxima during the cycle; the second maximum of cytochromes a+a(3) was coincident with a maximum of activity of enzymically active cytochrome c oxidase. 7. The amount of cytochrome P-420 decreased during the first three-quarters of the cell-cycle, whereas that of cytochrome P-450 increased during this period. 8. The discrepancy between spectrophotometric and enzymic assay of cytochrome c oxidase, the changing ratio of cytochrome a(3)/cytochrome a and the relationship between changes in cellular content of cytochromes and previous observations on respiratory oscillations during the cell cycle are discussed.

Ascomycota↗