A phosphodiester bridge between two arabinose residues as a structural element of an extracellular glycöprotein of Volvox carteri

The sulphated glycoprotein SSG 185 is the monomeric precursor of a highly aggregated structural element in the extracellular matrix of the multicellular green alga Volvox carteri. A phosphodiester of arabinose was isolated from a saccharide fragment of SSG 185. The structure of this phosphodiester was investigated by methylation analysis, 13C‐NMR, photometric methods and enzymatic assays and identified as d‐Araf‐5‐phospho‐5‐d‐Araf. The function of this phosphodiester bridge as a crosslink of different carbohydrate chains in SSG 185 is discussed.