The structure-function relationship of a gellan family of polysaccharides, S-198 gum produced by Alcaligenes ATCC31853 was investigated in terms of rheological aspects. The flow curves of S-198 gum showed plastic behavior above 0.3%. Gelation did not occur in S-198 gum solution at low temperature (0˚C), even at 0.8%. Both the viscosity and the elastic modulus remained constant with increasing temperature up to 80˚C. The elastic modulus decreased a little with the addition of CaCl2 (6.8 mM), but then once again remained constant up to 80˚C. The highest elastic modulus was observed for deacylated gellan gum with the addition of CaCl 2 and increased slightly with increasing temperature up to 80˚C, which was considered to be a transition temperature, after which it decreased rapidly. The elastic modulus of S-198 gum in the presence of urea (4.0 M) was lower than that in aqueous solution at low temperature (0˚C), but remained constant with increasing temperature up to 80˚C. The intramolecular associations, (hydrogen bonding and van der Waals forces of attraction), of S-198 gum molecules in aqueous solutions were proposed. The gellan family of polysaccharides, S-198, S-88, S-657, rhamsan, welan and gellan gum, provided a good opportunity to investigate the structure-function relationship for polysaccharides.

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Background: A brown seaweed, Saccharina longissima (Laminaria angustata var. longissima) has been consumed in Okinawa for 300 years. It is native to the southernmost part of Japan, in Okinawa, but grows on the Pacific coast (Kushiro and Nemuro) in Hokkaido in the northernmost part of Japan. Previously, we reported the structural characteristics from S. longissima. The fucoidan consisted of L-fucose, D-galactose, D-glucose, D-xylose, D-glucuronic acid, and sulfuric acid. This fucoidan activated the RAW 264.7 murine macrophage cell line. The aim of this study was to investigate the effects of a fucoidan isolated from Saccharina longissima on cell anti-proliferation and apoptosis in the U937 human leukemia monocyte lymphoma cell line. Methods: U937 cells were incubated with four fucoidan concentrations. The degree of apoptosis was determined using the APOPercentage APOPtosis assay, caspaer-3 activity assay and Western blotting analysis assay. Results: The treatment of cell with a fucoidan highly substituted with sulfate, in addition to L-fucose residues, inhibited cell growth. Apoptosis increased in U937 cells in a dose-dependent manner following the addition of fucoidan. However, the fucoidan did not induce apoptosis in the presence of caspase inhibitor (z-VAD-FMK).Conclusions: The fucoidan from Saccharina longissima induced apoptosis in U937 cells. Accordingly, the kelp containing this fucoidan may contribute to the observed longevity of the Okinawan population.Keywords: fucoidan, Saccharina longissimi, brown seaweed, traditional food, human leukemia cells, apoptosis