Cation specificity and cation binding to low sulfated carrageenans

Abstract

A low-sulfated carrageenan from Eucheuma gelatinae and a partially desulfated (by chemical means) furcellaran were studied by polarimetry and Cs-133 NMR. The polarimetric studies show that the cation specificity of the coil-helix transition remains a strong effect even for very low-sulfated carrageenans, whereas the sensitivity to inert salt is considerably weakened compared to unmodified furcellaran. Cs-133 NMR shifts and linewidths reveal a binding of Cs + to the helical conformation, but not to the random coil. The cation specificity is well predicted by the theoretical model previously used for unmodified furcellaran and kappa-carrageenan, if it is assumed that the intrinsic binding constant and the density of binding sites are independent of the degree of sulfation of the carrageenan helix.