Surface potential changes on energization of mycoplasma cell membranes.

The membrane surface potential of mycoplasma cells was measured by changes in the partition between the membrane and the aqueous environment of the impermeable cationic amphipatic spin probe 4-(N,N-dimethyl-N-nonyl)ammonium-2,2,6,6-tetramethylpiperidine-1-oxyl (CAT9). Upon energization of glycolyzing mycoplasma cells, the outer surface of these membranes becomes more negatively charged. The effects of uncouplers further indicate that this change in surface potential appear to be dependent on the existence of a delta pH across the membranes.