Role of NADH oxidase in the oxidative inactivation of Streptococcus salivarius fructosyltransferase

A cell-associated fructosyltransferase produced by Streptococcus salivarius was irreversibly inactivated in a time-dependent manner when resting or permeabilized cell suspensions were incubated with low concentrations (less than 1.0 microM) of copper. In addition to copper, the inactivation was dependent on oxygen and on a fermentable carbon source (endogenous intracellular polysaccharide or glucose). In starved, permeabilized cell suspensions, the fermentable carbon source could be replaced by NADH but not by NADPH or ATP. Of several other S. salivarius enzymes tested, only fructosyltransferase was inactivated under these conditions. The available evidence indicated that NADH oxidase is the enzyme responsible for fructosyltransferase inactivation. Results from oxygen radical scavenger studies implicated one or more species of oxygen radicals and hydrogen peroxide in the inactivation reaction.