STUDIES OF A PHOSPHOLIPID-REQUIRING BACTERIAL ENZYME .2. ROLE OF PHOSPHOLIPID IN URIDINE DIPHOSPHATE GALACTOSE - LIPOPOLYSACCHARIDE ALPHA-3-GALACTOSYL TRANSFERASE REACTION

Phospholipid is required as a cofactor in the reaction catalyzed by uridine diphosphate galactose:lipopolysaccharide α-3-galactosyl transferase. The role of phospholipid was studied, using an extensively purified preparation of the enzyme. The technique of equilibrium density gradient centrifugation was used to determine the ability of different phospholipids to form binary complexes with lipopolysaccharide or with enzyme. Certain phospholipids formed binary complexes with lipopolysaccharide but not with enzyme; others formed binary complexes with enzyme but not with lipopoly saccharide. Both of these types of phospholipid were inactive in the enzyme system. In contrast, phospholipids which were able to form binary complexes both with lipopolysaccharide and with enzyme were active. The data suggest a model in which the enzyme reaction involves binding of phospholipid to both the lipopolysaccharide substrate and to the enzyme protein. © 1969, American Chemical Society. All rights reserved.