Urease Activity and Ascorbic Acid

Abstract

WITH reference to Mr. Elson's observation¹ that ascorbic acid at low concentrations inhibits urease activity, and that this inhibition disappears in the presence of cysteine, it is worth noting that certain polyhydric phenols, for example, catechol and quinol, also exert at low concentrations (one part in two millions) highly inhibitory effects on urease activity, this inhibition disappearing in presence of thiol compounds such as cysteine². It has been shown that the inhibition in this case is due, not to the phenol, but to the corresponding oxidized product, that is, the quinone present in solution with the phenol. The alleviating action of cysteine is due to the reduction of the quinone to the inert phenol. It may be suggested that, in an analogous manner, the toxicity of ascorbic acid in dilute solution is due to the oxidized form of ascorbic acid, namely, the diketone, present in solution, and not to the ascorbic acid itself. The effect of cysteine will be to reduce the dehydro-ascorbic acid to the inert ascorbic acid, a phenomenon which is known to take place, as shown by Crook³.