Urease activity and L-ascorbic acid.

In this work, we studied the behaviours of urease in the presence of l-ascorbic acid (AA) and dehydroascorbic acid (DHA) in different conditions. The inactivations of urease were carried out in an unbuffered and buffered system. We show that in the unbuffered system AA inactivated urease in a biphasic manner by denaturation brought about by AA-lowered pH. Further, we show that in the buffered system neither AA nor DHA themselves are inhibitors of urease. The inhibitory action of AA and DHA was revealed in the presence of Fe(3+) ions and most importantly, unlike reported in the literature, it was found to be primarily mediated by H(2)O(2). The resulting inhibition by DHA-Fe(3+) consisted of enzyme thiol oxidation and its effectiveness grew with increasing pH. The results may shed light on the roles of AA in therapies applied in ureolytic bacteria infections, notably those with Helicobacter pylori.