RESUMO
Non-saponifiable cell extracts of wild type and sterol mutants of N. crassa were analysed by means of gas-liquid chromatography. The wild-type contained ergosterol and episertol in a 10:1 ratio. None of the mutants was able to synthesize ergosterol. Three of the mutants carry single recessive gene mutations cauisng blocks in the terminal steps of ergosterol biosynthesis: erg-1 has an inactive delta 8 leads to delta 7 isomerase erg-2 has an inactive 24(28) hydrogenase, and erg-4 has an inactive C-24 methyl transferase. Some of the mutants accumulated novel sterols as a result of their enzyme defects. The genes erg-1 and erg-2 were mapped close to inl on the right arm of chromosome V.
Assuntos
Resistência Microbiana a Medicamentos , Ergosterol/metabolismo , Neurospora crassa/genética , Neurospora/genética , Nistatina/farmacologia , Esteróis/metabolismo , Mutação , Neurospora crassa/metabolismo , FenótipoRESUMO
Parenchymal cells from adult rat liver, isolated by a collagenase perfusion technique, have been maintained in primary culture and a detailed study on carbohydrate metabolism carried out over the initial 48-hour culture period. The glucose concentration of the medium exerts a major influence on glycogen accumulation by the cells. Insulin, particularly at high glucose concentrations, stimulates glycogen biosynthesis, whereas glucagon prevents glycogen accumulation. Dexamethasone was without effect on glycogen metabolism. Glucose appears to stimulate glycogen accumulation by activation of glycogen synthetase enzyme. However, there is a gradual loss of synthetase activity throughout the culture period. Similar decreases in activity were noted for pyruvate kinase, aldolase and hexokinase. Glucose, insulin and dexamethasone were unable to prevent these decreases in enzyme activity. Foetal bovine serum contains fructose and this hexose appears to be the factor in serum which is responsible for the activation of glycogen accumulation in the presence of physiological glucose concentrations. The lactic acid content of the serum may also stimulate glycogen accumulation. In general, there is a gradual loss of the pattern of carbohydrate metabolism typical of differentiated hepatocytes during the culture period.
Assuntos
Células Cultivadas/metabolismo , Dexametasona/farmacologia , Glucagon/farmacologia , Insulina/farmacologia , Glicogênio Hepático/metabolismo , Soroalbumina Bovina/farmacologia , Animais , Células Cultivadas/enzimologia , Meios de Cultura , Frutose/metabolismo , Frutose-Bifosfato Aldolase/metabolismo , Glucose/metabolismo , Glicogênio/biossíntese , Glicogênio Sintase/metabolismo , Hexoquinase/metabolismo , Fígado , Piruvato Quinase/metabolismo , RatosRESUMO
A mutant (erg-3) of Neurospora crassa resistant to the polyene antibiotic nystatin was compared with its sensitive, wild-type parent to detect differences in sterol composition using gas chromatography-mass spectrometry. The major sterol in wild-type mycelia, comprising 80% of the total, was ergosterol. The major sterols in mutant mycelia, comprising 86% of the total, were delta 8,14-sterols. It is proposed that the nystatin-resistant strain is unable to synthesize ergosterol because it lacks delta 14,15-reductase activity as a result of a mutation in the erg-3 gene.