No abstract

A mutant, URT-43, was isolated from E. coli C600 dur+. The mutant has a characteristic feature in that its sensitivity to ultraviolet (u.v.) light is greatly influenced by the temperature at which irradiated bacteria are incubated. On the basis of dose-reduction factor, URT-43 is approximately ten times more sensitive at 42" than at 30"C, even though unirradiated bacteria are not thenno-sensitive, The mutant could not repair u.v.-irradiated bacteriophage Avir in the dark either at 30" or at 4 2 T , indicating that it is defective in host-cell reactivation. In contrast, the same bacteriophage was reactivated in preirradiated URT-43 if the host-bacteriophage complex was plated at 30" but there was no reactivation at 42°C. Therefore u.v.reactivation was positive at 30" but negative at 42°C. The induction of prophage by URT-43(Ah) was achieved by much lower doses of U.V. light than that required for the induction of lysogenic wild type bacteria. Experiments were performed in which irradiated URT-43 was first incubated for various periods in liquid media and plated both at 30" and 42°C. It was found that irradiated bacteria came to be resistant to subsequent plating at 42" only when they were preincubated in the liquid medium containing necessary amino acids and at 30°C. Since this phenomenon was completely inhibited by chloramphenicol, the process seemed to require de novo protein synthesis. An hypothesis was proposed that there are at least two independent dark-repair mechanisms in E. coti; one is responsible for host-cell reac!ivation and the other is responsible for U.V. reactivation.

O isolamento de substâncias a partir de drogas vegetais é realizado com freqüência empregando-se métodos cromatográficos, sendo a cromatografia em coluna a mais utilizada. Uma variante da cromatografia em coluna é a cromatografia líquida a vácuo, por ser uma técnica eficiente e de baixo custo, podendo ser empregada com fins analíticos qualitativos ou mesmo quantitativos. Através de extratos semipurificados, e com auxílio da cromatografia líquida a vácuo, isolou-se 3-O-metilquercetina de Achyrocline satureioides (Lam.) DC., Asteraceae, obtendose um teor de 1,21%.