CONFIRMATION OF THE STRUCTURE OF LIPID-A DERIVED FROM THE LIPOPOLYSACCHARIDE OF RHODOBACTER-SPHAEROIDES BY A COMBINATION OF MALDI, LSIMS, AND TANDEM MASS-SPECTROMETRY

The chemical structure of nontoxic diphosphoryl lipid A from Rhodobact er sphaeroides was confirmed using a combination of LSIMS (on a two-se ctor mass spectrometer) and MALDI (on time-of-flight and ion trap mass spectrometers) in conjunction with tandem mass spectrometry in both p ositive and negative ion modes. Accurate molecular weight measurement accompanied by the analysis of fragment ion masses yielded the composi tion of fatty acyl groups. Tandem experiments (collisionally induced d issociation of both quasimolecular and oxonium ions) were also perform ed, revealing the precise location and nature of the fatty acyl groups on the disaccharide backbone.