Macrophage stimulation activity of the polysaccharide fraction from a marine alga (Porphyra yezoensis): structure-function relationships and improved solubility.

The polysaccharide fraction from Porphyra yezoensis (PASF) has already been shown to stimulate murine phagocytic functions in vivo and in vitro [Y. Yoshizawa et al., Biosci. Biotech. Biochem., 57, 1862-1866 (1993)]. In this study, various treatments were applied to PASF to assess its structure-function relationships. Desulfation of PASF decreased in vitro macrophage-stimulation activity, while further sulfation of PASF did not change the activity. Among 7 fractions obtained by anion-exchange chromatography of PASF, stronger activity was found in the fractions having a lower or higher sulfate content than in those having a medium sulfate content. Digests of PASF with beta-agarase showed higher activity and solubility, and lower viscosity, than undigested PASF. These results indicate that the sulfate groups in PASF, probably porphyran, contributed to the macrophage stimulating activity, although a larger number of sulfate groups did not always cause stronger activity.