PROTEOGLYCANS FROM THE GUM EXUDATE OF MYRRH

The watersoluble gum fraction of myrrh (40% w/w), has been found to co mprise of a heterodisperse mixture of proteoglycans with dominating am ounts 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% an d Hyp as the main amino acid (40%). Structural investigations using mi ld acid hydrolysis, Smith degradation and alkaline hydrolysis demonstr ated that two different types of sugar chains are linked to the protei n-core. These comprise either of short chains of arabinose or of sligh tly branched chains composed of galactose and 4-O-methyl-glucuronic ac id. Both structures are linked to the protein moiety via Hyp. As the g alactose is substituted at C4 with 4-O-methyl-glucuronic acid, which i s substituted at C2 with galactose, for this specific structure the te rm ''4-O-methyl-glucurono-galactan'' is proposed. It has not yet been reported in any other gum described so far. Gum myrrh containes furthe rmore arabino-3.6-galactan-protein fractions with an average molecular weight of about 70 000 and a protein amount of 31 and 16%, respective ly. It can not be concluded whether the different types of proteoglyca ns 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 Eu ropean Pharmacopea.