Studies on the Protein Moiety of Endotoxin from Gram-Negative Bacteria: Characterization of the Enzymatically Degraded Protein Moiety Isolated by Phenol Treatment of Endotoxin from S. marcescene 08

The simple protein of endotoxin from Serratia marcescens 08 was treated successively with trypsin and pronase. The resulting trypsin and pronase cores contained increasing amounts of lipid A constituents firmly bound to the residual protein moiety. Since lipid A was separated as an entity from the protein moiety only after acid hydrolysis of the pronase core, it is proposed that in intact endotoxin lipid A is covalently linked to the protein moiety. The absence of any detectable glucosamine and fatty acids in the mixture of peptides and amino acids released by trypsin and pronase, indicated a single point attachment between the lipid A and protein moieties. Both trypsin and pronase cores were immunogenic and revealed the presence of a common antigenic determinant with the parent simple protein. The second set of antigenic determinants different from the specific O-antigens is located in the protein moiety close to lipid A.