Two Forms of a Structural Lipoprotein in the Envelope of Escherichia coli

Abstract

Abstract A major envelope protein of Escherichia coli was previously found to exist in two different forms in the cell envelope: the free form and the bound form which is covalently linked to the peptidoglycan. Chemical properties of the free form were further investigated and compared with those of the bound form. The envelope fraction labeled with both [14C]palmitic acid and [3H]arginine was analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis after removal of phospholipid by extensive extraction with the mixture of chloroform and methanol (2:1). The palmitic acid content of the free form was found to be identical with that of the bound form on the basis of their arginine contents. As in the case of the bound form, palmitic acid was released from the free form by both alkali and acid hydrolysis. This suggests that palmitic acid attaches to the free form by both ester and amide linkages. It was also found that the free form contained neither diaminopimelic acid nor glucosamine. Preliminary purification of the free form of the lipoprotein is also reported.