title: Enzymic activity of the K5-type yeast killer toxin and its characterization.
abstract: K5-type yeast killer toxin secreted by P. anomala NCYC 434 cells has a broad killing spectrum. Competitive inhibiton of killer activity showed that glucans, mainly the beta-1,3 glucan, represent the primary toxin binding site within the cell wall of sensitive cells. Its hydrolytic activity on laminarin in an exo-like fashion revealed that the toxin exerts its killing effect by exo-beta-1,3-glucanase activity. Its specific activity on laminarin was 120 U/mg, and the Michaelis constants K(m) and V(max) for laminarin hydrolysis were 0.25 mg/ml and 370 micromol/min/mg. The toxin exerted its cytocidal effect after 2 h contact with the target cells. Production of the toxin by the cells was induced only when they were grown in culture media rich in beta-glucan sources, and the addition of glucose increased the specific production rate. The enzymic activity of the toxin was fully inhibited by Hg(+2), but increased with some other metal ions, most of all by Pb(+2).
authors.affiliation: Department of Biological Sciences, Middle East Technical University, Ankara, Turkey. izgu@metu.edu.tr
authors.forename: Fatih
authors.initials: F
authors.lastname: Izgü
authors.forename: Demet
authors.initials: D
authors.lastname: Altinbay
authors.forename: Abdullah
authors.initials: A
authors.lastname: Sertkaya
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive; D043326:Glucan 1,3-beta-Glucosidase / Q000378:metabolism*; D005936:Glucans / Q000378:metabolism*; D007700:Kinetics; D009183:Mycotoxins / Q000378:metabolism / Q000494:pharmacology*; D011134:Polysaccharides / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000166:cytology / Q000187:drug effects; D015003:Yeasts
chemical_list: D005936:Glucans; D009183:Mycotoxins; D011134:Polysaccharides; C008247:laminaran; D043326:Glucan 1,3-beta-Glucosidase