Location of some proteins involved in peptidoglycan synthesis and cell division in the inner and outer membranes of Escherichia coli

Inner and outer membranes of Escherichia coli were separated by isopycnic centrifugation in sucrose gradients and analyzed for the presence of penicillin-binding proteins. All penicillin-binding proteins--except penicillin-binding protein 3, which is found almost exclusively in the cytoplasmic membrane and is involved in septum formation--are also found in gradient fractions corresponding to the outer membrane. Our results support the hypothesis that approximately half of the total amount of penicillin-binding proteins may be sacculus-located proteins linked to the outer membrane, probably through peptidoglycan bridges.