ABSTRACT
In Gram-negative organisms the periplasm is surrounded by an outer membrane which is interconnected with the peptidoglycan layer through a covalently bound lipoprotein known as Braun lipoprotein. 19 In addition, there are lipoproteins noncovalently associated to peptidoglycan.' 9 - 21 The outer membrane is an asymmetric bilayered structure consisting of phospholipid in the inside half and lipopolysaccharide in the outside half of the bilayer. Transbilayer pore structures for specific molecules restrict molecular traffic from extracelluler environment into the periplasm.' 9 Proteins secreted into the periplasm may be incorporated into either layer of the outer membrane.
