Complex sentence: One of the sulfated ligands is chondroitin sulfate that is one type of glycosaminoglycan (GAG) and its activity in tumor metastasis has been revealed by the addition of heparin functioning as blocking tumor metastasis.
Split into simpler sentences: One of the sulfated ligands is chondroitin sulfate, a type of glycosaminoglycan (GAG). Its activity in tumor metastasis has been probed by the addition of heparin that functions to blocks tumor metastasis.