RESUMEN
The possible role of free hydroxyl radicals in the oxidation of cyclohexanol to cyclohexanone and of benzene to phenol was examined in a reconstituted system containing rabbit phenobarbital-inducible P-450LM2. From steady state kinetic studies, a KM for cyclohexanol of 8.7 mM and a Vmax of 5.7 nmol of cyclohexanone formed/min/nmol of P-450 were determined. Similarly, a KM for benzene of 105 mM and a Vmax of 22 nmol of phenol formed/min/nmol of P-450 were obtained. With intact microsomes from phenobarbital-treated rabbits, a KM for benzene of 18 mM and a Vmax of 1.7 nmol of phenol formed/min/nmol of P-450 were determined. With the use of substrate concentrations in the range of the respective KM values, superoxide dismutase, desferrioxamine, and dimethyl sulfoxide were found to have no significant effect on the P-450-catalyzed reactions. When the oxidation of benzene or cyclohexanol was examined in a model hydroxyl radical-generating system containing xanthine, xanthine oxidase, and Fe-EDTA, no dependence of the rate of oxidation on the substrate concentrations used was observed. Since the rate of hydroxyl radical generation by the model system was adjusted to be greater than the rate of product formation in the P-450 system, the lack of dependence on substrate concentration suggests that free hydroxyl radicals are not involved in the P-450-catalyzed reactions studied. Taken together, these findings indicate that the free hydroxyl radical-mediated pathway observed by other investigators does not contribute significantly to product formation when these substrates are present at concentrations within the range of their respective KM values.
Asunto(s)
Benceno/metabolismo , Ciclohexanoles/metabolismo , Sistema Enzimático del Citocromo P-450/metabolismo , Hidróxidos/metabolismo , Microsomas Hepáticos/metabolismo , Animales , Ciclohexanonas/biosíntesis , Radicales Libres , Radical Hidroxilo , Masculino , Oxidación-Reducción , Fenol , Fenoles/biosíntesis , ConejosRESUMEN
Three cyclitol derivatives, 2,4/3-triacetoxycyclohexanone diethyl dithioketal (XVIII), and 2,3,4-tri-O-acetyl-1-O-ethyl-2,4/1,3-cyclohexanetetrol (XXA) and 2,3,4-tri-O-acetyl-1-O-ethyl-1,2,4/3-cyclohexanetetrol (XXB), have been synthesized via the cyclisation of 2,3,4-tri-O-acetyl-5,6-dideoxy-D-xylo-hex-5-enose diethyl dithioacetal (XIV) and the cyclisation of 2,3,4-tri-O-acetyl-5,6-dideoxy-D-xylo-hex-5-enose diethyl acetal (XV) under ultraviolet or direct sunlight, in aqueous acetone.
Asunto(s)
Antibacterianos/biosíntesis , Fenómenos Químicos , Química , Ciclización , Ciclohexanoles/biosíntesis , Ciclohexanonas/biosíntesis , Conformación Molecular , FotólisisRESUMEN
A strain of Aspergillus fumigatus (Fresenius) isolated from a milk food for calves was grown on a culture medium containing added saccharose. The purpose was to study the synthesis of two recently discovered mycotoxins, fumigatin and spinulosin. The work was performed under many different conditions of temperature, pH and inoculum. These mycotoxins were measured by analytical differential pulse polarography. Correlations were observed between the growth rate of A. fumigatus and variation in pH of the medium and the formation of fumigatin, which is only possible when pH falls to less than 4.0. Fumigatin appears promptly at the beginning of the growth phase of the fungus but quickly disappears. The production of metabolite depends on limited conditions of culture. Spinulosin, very similar to fumigatin, is substituted for fumigatin in slightly different conditions. During growth, the fungus degrades both metabolites. The nature of the substitution and the reason of these modifications have not been investigated. Fumigatin and spinulosin formation is observed in both toxigenic and non-toxigenic strains.