Proteoglycans from the gum exudate of myrrh

The watersoluble gum fraction of myrrh (40% w/w), has been found to comprise of a heterodisperse mixture of proteoglycans with dominating amounts of uronic acid rich polymers. The major fraction (70% w/w) was a proteoglycan (M(r) similar to 200 000) with protein content of 10% and Hyp as the main amino acid (40%). Structural investigations using mild acid hydrolysis, Smith degradation and alkaline hydrolysis demonstrated that two different types of sugar chains are linked to the protein-core. These comprise either of short chains of arabinose or of slightly branched chains composed of galactose and 4-O-methyl-glucuronic acid. Both structures are linked to the protein moiety via Hyp. As the galactose is substituted at C4 with 4-O-methyl-glucuronic acid, which is substituted at C2 with galactose, for this specific structure the term ''4-O-methyl-glucurono-galactan'' is proposed. It has not yet been reported in any other gum described so far. Gum myrrh containes furthermore arabino-3.6-galactan-protein fractions with an average molecular weight of about 70 000 and a protein amount of 31 and 16%, respectively. It can not be concluded whether the different types of proteoglycans represent the naturally occurring diversity of polymers or whether they derive from degradation processes during isolation or storage of the commercial sample of myrrh, as it is used in the purview of the European Pharmacopea.