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Abstract
The transverse distribution of phosphatidyiglycerol (PG) across the inner membrane of Escherichia coli was studied. The oxidation of PG by periodate was used to discriminate between the PG present in the cytoplasmic and in the periplasmic leaflet of the inner membrane. Applied to large unilamellar vesicles derived of an E. coli lipid extract, the periodate method demonstrated the expected symmetrical distribution of PG over the bilayer. However, both in right-side-out and in Inside-out inner membrane vesicles isolated from E. coli, as well as In intact E. coli cells, the entire pool of PG was oxidized by periodate. The oxidation reaction proceeded at such a high rate that it was impossible to determine the distribution of PG across the membrane. Apparently, periodate easily permeates through the membrane. This permeation could not be inhibited or slowed down, and it was concluded that the use of periodate as oxidizer of PG is not a suitable method to determine the transverse distribution of this phospholipid in the Gram-negative bacterium E. coli. However, periodate can be used to selectively modify the total PG pool in this organism.