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Biomedical subjects

D E Griffiths

Publications and source records attributed to D E Griffiths.

At least 55 records · Page 3Linked to original sources
PubMed1977

Extra-chromosomal inheritance of rhodamine 6G resistance in Saccharomyces cerevisiae.

Rhodamine 6G was found to be a specific inhibitor of aerobic growth of yeast, having no effect on fermentative growth. A single step spontaneous mutant of S. cerevisiae resistant to rhodamine 6G was isolated, which showed cross-resistance to the ATPase inhibitors venturicidin and triethyltin, to the uncoupler 1799, to bongkrekic acid and to cycloheximide, but not to oligomycin or to the inhibitors of mito chondrial protein synthesis, chloramphenicol and erythromycin. The genetic analysis of this mutant showed that both nuclear and cytoplasmic (but apparently not mitochondrial) factors may be involved in the determination of the mutation. The behaviour is discussed as a possible function for 2 micron circular (omicron) DNA.

Cross Reactions↗
PubMed1976

Studies of energy-linked reactions. Net synthesis of adenosine triphosphate by isolated adenosine triphosphate synthase preparations: a role for lipoic acid and unsaturated fatty acids.

ATP synthase preparations [complex V, proton-translocatin ATPase (adenosine triphosphatase) and oligomycin-sensitive ATPase ] contain stoicheiometric amounts of lipoic acid residues (up to 6mol of lipoic acid/mol of ATPase complex) and catalyse net ATP synthesis in an uncoupler-and oligomycin-sensitive reaction utilizing dihydrolipoate, oleoyl-CoA and oleic acid, or in a reaction utilizing oleoyl-S-lipoate. The terminal reactions of oxidative phosphorylation are thus analogous to those of substrate-level phosphorylation.

Adenosine Triphosphatases↗
PubMed1975

Studies on energy-linked reactions: isolation, characterisation and genetic analysis of trialkyl-tin-resistant mutants of Saccharomyces cerevisiae.

Mutants of Saccharomyces cerevisiae resistant to triethyl tin sulphate have been isolated and are cross-resistant to other trialkyl tin salts. Triethyl-tin-resistant mutants fall into two general phenotypic classes: class 1 and class 2. Class 1 mutants are cross-resistant to a variety of inhibitors and uncoupling agents which affect mitochondrial membranes (oligomycin, ossamycin, valinomycin, antimycin, erythromycin, chloramphenicol, '1799', tetrachlorotrifluoromethyl benzimidazole carbonylcyanide-m-chlorophenylhydrazone and cycloheximide). Class 2 mutants are specifically resistant to trithyl tin and the uncoupling agent "1799' [bis-(hexafluoroacetonyl)-acetone]. Triethyl tin at neutral pH values is a specific inhibitor of mitochondrial energy conservation reactions and prevents growth on oxidisable substrates such as glycerol and ethanol. Triethyl-tin-resistant mutants grow normally on glucose and ethanol in the presence of triethyl tin (10 muM). Biochemical studies indicate that the mutation involves a modification of the triethyl tin binding site on the mitochondrial inner membrane, probably the ATP-synthetase complex. Triethyl tin resistance/sensitivity in yeast is determined by cytoplasmic (mitochondrial) and nuclear genes. The mutants fall into a nuclear and a cytoplasmic (mitochondrial) class corresponding to the phenotypic cross-resistance classes 1 and 2. In the cytoplasmic mutants the triethyl tin resistance segregates mitotically and the resistance determinat is deleted by the action of ethidium bromide during petite induction. Recombination studies indicate that the triethyl tin mutations are not allelic with the other mitochondrial mutations at the loci RI, RIII and OLI. This indicates that the binding or inhibitory sites of oligomycin and triethyl tin are not identical and that the triethyl tin binding site is located on a different mitochondrial gene product to those which are involved in oligomycin binding. Interaction and cooperative effects between different binding sites on the mitochondrial inner membrane have been demonstrated in studies of the effect of the insertion of the TETr phenotype into mitochondrial oligomycin-resistant mutants and provide an experimental basis for complementation studies at the ATP-synthetase level.

Adenosine Triphosphatases↗
PubMed1975

Studies on energy-linked reactions: isolation and properties of mitochondrial venturicidin-resistant mutants of Saccharomyces cerevisiae.

Venturicidin is a specific inhibitor of aerobic growth of yeast and has no effect on fermentative growth, a result which is consistent with its known mode of action on mitochondrial oxidative phosphorylation. Venturicidin-resistant mutants of Saccharomyces cerevisiae have been isolated and form two general classes: class 1, nuclear mutants which are resistant to a variety of mitochondrial inhibitors and uncouplers, and class 2, mitochondrial mutants of phenotype VENR OLYR and VENR TETR in vivo. VENR OLYR mutants show a high degree of resistance to venturicidin and oligomycin at the whole cell and mitochondrial ATPase level but, in contrast, no resistance at the mitochondrial level is observed with VENR TETR mutants. Venturicidin resistance/sensitivity can be correlated with two binding sites on mitochondrial ATPase, one of which is common to the oligomycin binding site and the other is common to the triethyl tin binding site. Biochemical genetic studies indicate that two mitochondrial genes specify venturicidin resistance/sensitivity and that the mitochondrial gene products are components of the mitochondrial ATPase complex.

Adenosine Triphosphatases↗
PubMed1975

Studies on energy-linked reactions: genetic analysis of venturicidin-resistant mutants.

Genetic analysis of venturicidin-resistant mutants has revealed the presence of both nuclear and mitochondrial genes responsible for determining venturicidin sensitivity/resistance in Saccharomyces cerevisiae. Recombination studies show that the mutation with phenotype VENR is situated at mitochondrial locus OL I and is therefore extremely useful of future genetic manipulations as it gives a unique phenotype to this locus distinguishable from the second oligomycin locus OL II. The mutations with phenotype VENR OLYR are linked to oligomycin locus OL I and have been allocated a new mitochondrial locus, namely OL III. Three factor croses involving the venturicidin mutations at loci OL I and OL III have shown them to freely recombine with the other mitochondrial loci R I, R III and OL II. The mitochondrial genetic map is therefore represented as four 'recombinational linkage groups'. A fifth linkage group is also specified for mutants with phenotype VENR TETR, and is probably located on a separate DNA molecule from the four other groups.

Antifungal Agents↗
PubMed1975

Phase transitions in yeast mitochondrial membranes. The effect of temperature on the energies of activation of the respiratory enzymes of Saccharomyces cerevisiae.

The effect of temperature on the activation energies of mitochondrial enzymes of the yeast Saccharomyces cerevisiae was examined. Non-linear Arrhenius plots with discontinuities in the temperature range 14-19 degrees C and 19-22 degrees C were observed for the respiratory enzymes and mitochondrial ATPase (adenosine triphosphatase) respectively. A straight-line Arrhenius plot was observed for the matrix enzyme, malate dehydrogenase. The activation energies of the enzymes associated with succinate oxidation, namely, succinate oxidase, succinate dehydrogenase and succinate-cytochrome c oxidoreductase, were in the range 60-85kJ/mol above the transition temperature and 90-160kJ/mol below the transition temperature. In contrast, the corresponding enzymes associated with NADH oxidation showed significantly lower activation energies, 20-35kJ/mol above and 40-85kJ/mol below the transition temperature. The discontinuities in the Arrhenius plots were still observed after sonication, treatment with non-ionic detergents or freezing and thawing of the mitochondrial membranes. Discontinuities for cytochrome c oxidase activity were only observed in freshly isolated mitochondria, and no distinct breaks were observed after storage at -20 degrees C. Mitochondrial ATPase activity still showed discontinuities after sonication and freezing and thawing, but a linear plot was observed after treatment with non-ionic detergents. The results indicate that the various enzymes of the respiratory chain are located in a similar lipid macroenvironment within the mitochondrial membrane.

Adenosine Triphosphatases↗
PubMed1975

Membrane-lipid unsaturation and mitochondrial function in Saacharomyces cerevisiae.

The lipid composition of yeast cells was manipulated by the use of an unsaturated fatty acid auxotroph of Saccharomyces cerevisiae. There was a 2-3-fold decrease in the concentration of cytochromes a+a3 when the unsaturated fatty acid content of the cells was decreased from 60-70% of the total fatty acid to 20-30%. The amounts of cytochromes b and c were also decreased under these conditions, but to a lesser extent. Further lipid depletion, to proportions of less than 20% unsaturated fatty acid, led to a dramatic decrease in the content of all cytochromes, particularly cytochromes a+a3. The ATPase (adenosine triphosphatase), succinate oxidase and NADH oxidase activities of the isolated mitochondria also varied with the degree of unsaturation of the membrane lipids. The lower the percentage of unsaturated fatty acid, the lower was the enzymic activity. Inhibition of mitochondrial ATPase by oligomycin, on the other hand, was not markedly influenced by the membrane-lipid unsaturation. Npn-linear Arrenius plots of mitochondrial membrane-bound enzymes showed transition temperatures that were dependent on the degree of membrane-lipid unsaturation. The greater the degree of lipid unsaturation, the lower was the transition temperature. It was concluded that the degree of unsaturation of the membrane lipids plays an important role in determining the properties of mitochondrial membrane-bound enzymes.

Adenosine Triphosphatases↗