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.