Figure 7.

Schematic representations of the proposed depolymerization mechanism. HLGAG–heparinase I interactions that determine the exolytic preference of initial cleavage of a substrate polymer are described by a subsite model (Upper). The significance of ΔG values for the individual subsites is explained in the text. The processive cleavage of several linkages of the same substrate molecule is shown (Lower). The relative position of heparinase I (large molecule) and substrate (copolymer of uronic acid (circles) and glucosamine (squares)) shifts from a position during previous bond cleavage (hatched) to the current position (gray). Uronic acid residues that make the H–U linkages resistant to heparinase I cleavage are shown in black. Arrows indicate the linkages cleaved.