The major repeating disaccharide unit in heparin is α-L-IdoA--SO_-β(→)-α-D-GlcNSO_ --SO_, which is called trisulfated di其主要重复双糖单位为-[-α-L-IdoA--SO_-β(→)-α-D-GcNSO_ --SO_-]-(又称三硫酸双糖单位)。