Specifically cleaves heparan sulfate-rich regions of acidic polysaccharides. Does not act on N,O-desulfated glucosamine or N-acetyl-O-sulfated glucosamine linkages. Functions in cleaving metazoan heparan sulfate and providing carbon, nitrogen and sulfate sources for microorganisms. Elimination of sulfate, appears to act on linkages between N-acetyl-D-glucosamine and uronate. Product is an unsaturated sugar. kcat is 94 sec(-1). kcat is 78 sec(-1) with recombinant enzyme. Belongs to the polysaccharide lyase 12 family. Extended N-terminus.