Résumé
The mode of sucrose utilisation by Corynebacterium murisepticum cells growing on M9 minimal medium supplemented with 0.4% sucrose as the carbon source was studied. It was observed that during growth of this organism, sucrose in the medium is hydrolysed to glucose and fructose, suggesting the formation of an extracellular invertase. Unlike in other microorganisms (e.g. Saccharomyces cerevisiae) the invertase formation is not repressed by the presence of glucose in the medium. The invertase was found to be the only predominant extracellular protein in the culture broth and could be purified in a single step by precipitation at 90% ammonium sulphate saturation. The purified protein had a molecular mass of 70,000 daltons. It not only showed invertase activity, but also a fructosyltransferase activity as it could convert sucrose to beta-1,2-difructose, as well as to glucose and fructose.
Sujets)
Chromatographie sur couche mince , Corynebacterium/enzymologie , Électrophorèse sur gel de polyacrylamide , Glycosidases/composition chimique , Masse moléculaire , Raffinose/métabolisme , Saccharose/métabolisme , beta-FructofuranosidaseRésumé
A sensitive assay for staphylococcal nuclease involving incubation of the enzyme sample with heat-denatured [3H]thymidine labelled DNA from E. coli, precipitation with trichloroacetic acid and measurement of the radioactivity of acid-soluble nucleotides released has been developed. The assay is sensitive enough to be used for comparing the levels of nucleases elaborated by different strains of S. aureus as well as for determining the extent of contamination of S. aureus in food and water samples even at levels at which the conventional spectrophotometric and toluidine blue-DNA methods are totally inadequate.