INCREASED CALCIUM AFFINITY OF A FUCOSYLATED CHONDROITIN SULFATE FROM SEA-CUCUMBER

Calcium binding and charge distribution on a fucosylated chondroitin s ulfate and a standard chondroitin 6-sulfate have been studied using a metallochromic indicator and conductimetric titrations. The fucosylate d chondroitin sulfate has a similar to 5-fold greater affinity for cal cium ions than the standard chondroitin 6-sulfate. Possibly, this incr eased affinity for calcium ions is due to the branches on the fucosyla ted chondroitin sulfate, since the calcium affinity of an unbranched, sulfated fucan is similar to that of the standard chondroitin 6-sulfat e. More charged groups per disaccharide unit (and a shorter distance b etween these groups) also distinguish the fucosylated chondroitin sulf ate from standard chondroitin 6-sulfate. Comparison between native and chemically modified (desulfated or carboxyl-reduced) polysaccharides suggests that the sulfate esters are responsible for the increased cha rge density of the fucosylated chondroitin sulfate and that the presen ce of the fucose branches does not alter the length of the repetitive units which compose the central core of chondroitin from sea cucumber. These results are consistent with the chemical studies of these two p olysaccharides.