Structural studies of the methylated, acidic polysaccharide associated with coccoliths of Emiliania huxleyi (Lohmann) Kamptner

Abstract

For the structure analysis of the methylated, acidic polysaccharide associated with the coccoliths of the alga Emiliania huxleyi (Lohmann) Kamptner, the native, the carboxyl-reduced, and the desulphated, carboxyl-reduced polysaccharides have been submitted to methylation analysis. Graded hydrolysis with acid, uronic acid degradation, and periodate oxidation/partial hydrolysis with acid in conjunction with methylation analysis were also applied. The results of the various degradation procedures have led to a proposed structure for the average unit of the polysaccharide. The mannan backbone consists of at least 80% of (1¨3)-linked D-mannosyl residues and has many side-chains. The mannan backbone carries ester-bound sulphate groups, terminal D-ribosyl or L-arabinosyl groups, and short side-chains of two or three D-galactosyluronic acid residues. There is also a complex side-chain composed of D-xylose and L-rhamnose, wherein the branched rhamnosyl residues are substituted by 3-O-methyl-D-xylose, 2,3-di-O-methyl-L-rhamnose, a di-(D-galactosyl-uronic acid)-D-xylosyl unit, and an oligosaccharide. The oligosaccharide is composed of 2,3-di-O-methyl-L-rhamnose, 3-O-methyl-D-galacturonic acid, 6-O-methyl-L-mannose, D-galacturonic acid, L-mannose, and L-rhamnose.