The Lipoprotein and Peptidoglycan of Rhodobacter sphaeroides

The lipoprotein-peptidoglycan complex (rigid layer) from Rhodobacter sphaeroides was iso­ lated. Treatm ent of the complex with N.O-diacetyl-muramidase cleaved off from the rigid layer the lipoprotein moiety with covalently bound peptidoglycan-fragments. The lipoprotein with the bound fragments showed a broad single band (M r about 19,000) on SDS-polyacrylamide gels and had an isoelectric point of about 5.6. There was no serological cross-reaction with the rigid layer of Escherichia coli K12. The lipid moiety of lipoprotein with residual amino acids (mainly Gly, Ser, Glu, Asp) was obtained by Pronase E treatm ent of the rigid layer and chloroform-methanol extraction. It was free from phosphate and contained amideand esterbound 18:1 and esterbound 16:0 and 18:0. The isolated peptidoglycan, after enzymatical cleavage from the lipoprotein, had a chemical composition indicating Aly-type structure. Comparable studies, performed with Rhodobacter capsulatus 37b4 resulted in essentially similar results for rigid layer, lipoprotein and peptidoglycan compositions.