DISTRIBUTION OF URONATE RESIDUES IN ALGINATE CHAINS IN RELATION TO ALGINATE GELLING PROPERTIES .2. ENRICHMENT OF BETA-D-MANNURONIC ACID ANDDEPLETION OF ALPHA-L-GULURONIC ACID IN SOL FRACTION

Alginate, a copolymer comprised of beta-D-mannuronic and alpha-L-gulur onic acid isolated from seaweeds and extruded by certain bacteria, for ms a gel in combination with several divalent cations. Polymer chains leaching out at 7-degrees-C, 24-degrees-C and 50-degrees-C from Ca-, a nd Sr-alginate gel beads were found to be depleted in alpha-L-guluroni c acid and enriched in beta-D-mannuronic acid compared to the starting material. For Sr gels. leached material is found to be almost devoid of alpha-L-guluronic acid triplets for the Sr gels, and a significant reduction in such triplets compared to the starting material was obser ved for the polymers leached from the Ca-gels. The leached material wa s also found to comprise the low-molecular-weight tail of the starting material molecular weight distribution, the truncation towards lower molecular weight was larger for the more block-like alginate. The chem ical composition of the leaching out from Sr-gels and Ca-gels suggests that 3 and 8 +/- 2 contiguous alpha-L-guluronic acid residues are req uired to form stable junction zones for Sr- and Ca-induced gelation re spectively.