title: Effect of Nitric Oxide on the Oxygen Metabolism and Growth of E. faecalis.
abstract: Gastro-intestinal mucosal cells have a potent mechanism to eliminate a variety of pathogens using enzymes that generate reactive oxygen species and/or nitric oxide (NO). However, a large number of bacteria survive in the intestine of human subjects. Enterococcus faecalis (E. faecalis) is a Gram-positive bacterium that survives not only in the intestinal lumen but also within macrophages generating NO. It has been reported that E. faecalis generated the superoxide radical (O(2) (-)). To elucidate the role of O(2) (-) and NO in the mechanism for the pathogen surviving in the intestine and macrophages, we studied the role and metabolism of O(2) (-) and NO in and around E. faecalis. Kinetic analysis revealed that E. faecalis generated 0.5 micromol O(2) (-)/min/10(8) cells in a glucose-dependent manner as determined using the cytochrome c reduction method. The presence of NOC12, an NO donor, strongly inhibited the growth of E. faecalis without affecting in the oxygen consumption. However, the growth rate of NOC12-pretreated E. faecalis in NO-free medium was similar to that of untreated cells. Western blotting analysis revealed that the NOC12-treated E. faecalis revealed a large amount of nitrotyrosine-posititive proteins; the amounts of the modified proteins were higher in cytosol than in membranes. These observations suggested that O(2) (-) generated by E. faecalis reacted with NO to form peroxinitrite (ONOO(-)) that preferentially nitrated tyrosyl residues in cytosolic proteins, thereby reversibly inhibited cellular growth. Since E. faecalis survives even within macrophages expressing NO synthase, similar metabolism of O(2) (-) and NO may occur in and around phagocytized macrophages.
authors.affiliation: Department of Biochemistry & Molecular Pathology, Osaka City Medical School, 1-4-3 Asahimachi, Abeno 545-8585, Japan.
authors.forename: Tomoko
authors.initials: T
authors.lastname: Nishikawa
authors.forename: Eisuke
authors.initials: E
authors.lastname: F Sato
authors.forename: Tina
authors.initials: T
authors.lastname: Choudhury
authors.forename: Kumiko
authors.initials: K
authors.lastname: Nagata
authors.forename: Emiko
authors.initials: E
authors.lastname: Kasahara
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Matsui
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Watanabe
authors.forename: Masayasu
authors.initials: M
authors.lastname: Inoue