Membrane locus and pH sensitivity of paraben inhibition of alkali production by oral streptococci

Parabens were found to be potent inhibitors of alkali production from argin ine by oral streptococci such as Streptococcus rattus, Streptococcus sangui s and Streptococcus gordonii. For example, 2 mu mol butylparaben per ml com pletely and irreversibly inhibited arginolysis by intact cells of S, rattus FA-1 and was lethal for the organism. In contrast, butylparaben was not a very effective inhibitor of ureolysis by intact cells of Streptococcus sali varius 57.I, although it did kill the cells. Butylparaben irreversibly inhi bited the cytoplasmic enzymes arginine deiminase, carbamate kinase and urea se in permeabilized cells or isolated form. However, inhibition of arginoly sis by intact cells appeared to be due primarily to irreversible inhibition of transport systems for arginine uptake, because butylparaben added to in tact cells did not reduce levels of arginine deiminase when the cells were subsequently permeabilized after washing. The insensitivity of ureolysis by intact cells to butylparaben can be related to the known high permeability of cell membranes to urea and the cytoplasmic location of urease. The pote ncy of butylparaben as an inhibitior of arginolysis or glycolysis and as a lethal agent was found to be greater at acid pH that at neutral or alkaline pH.