Abstract
By means of15N-tracer and oxidant pulse methods and with nitrate-grownParacoccus denitrificans it was found that KSCN completely inhibited reduction of N2O and nitrate in the 1 to 10 mM range, but had little or no effect on reduction of O2 or nitrite at 150 mM. These observations confirm a previous report. Potassium thiocyanate was insufficiently permeant across the cytoplasmic membrane ofParacoccus denitrificans andPseudomonas denitrificans even at 150 mM to prevent membrane polarization when oxidant pulses were large. Polarization and inhibition artifacts due to KSCN have created some confusion in the literature. Whereas valinomycin had little direct effect on reduction of nitrite, N2O, and O2 individually byPa. denitrificans, it caused a temporary nitrite-dependent inhibition of N2O reduction. Under nonpolarizing conditions the →H+/2e− ratios for O2, N2O, and nitrite (8.0, 4.3, and 4.5, respectively) confirmed those reported previously from this laboratory. The present results largely but not entirely agree with data from another laboratory.