Effect of oversulfation on the chemical and biological properties of kappa carrageenan

Kappa carrageenan was sulfated using chlorosulfonic acid–pyridine complex and isolated as the sodium salt. Infrared analysis of the native and sulfated kappa carrageenans gave identical results in respect to the O–H stretching, hemiacetal stretching and S=O stretching. Absorption around 845 cm−1 was also present in both the compounds representing the sulfate at the axial C-4 position except for a peak at 811 cm−1 which was only present in the oversulfated compound representing C-6 position. The sulfated compound showed 30 times higher anticoagulant activity in doubling prothrombin time of normal citrated human plasma in comparison with native compound. Studies on the effect of addition of the two kappa carrageenans during the in vitro activation of glutamic plasminogen (Glu-Plg) by tissue plasminogen activator(t-PA) or by urokinase(u-PA) showed that sulfated kappa carrageenan gave a 3-fold enhancement of the initial rate of the activation in comparison to control without the compound while the native kappa carrageenan or the unfractionated heparin were less active.