Polysaccharide lyase that catalyzes the depolymerization of several anionic polysaccharides via a beta-elimination mechanism. Exhibits broad substrate specificity, catalyzing the degradation of not only alginate and poly-beta-D-mannuronate (poly-ManA), but poly-beta-D-glucuronate (poly-GlcA or poly-GlcUA) and hyaluronate (HA) as well. The oligosaccharide products formed by enzymatic cleavage are comprised mainly of disaccharides, with a lower abundance of trimers and pentamers. Is not active on poly-D-galacturonate, heparin and heparin sulfate. Eliminative cleavage of alginate to give oligosaccharides with 4-deoxy-alpha-L-erythro-hex-4-enuronosyl groups at their non-reducing ends and beta-D-mannuronate at their reducing end. [hyaluronan](n) = n 3-(4-deoxy-beta-D-gluc-4-enuronosyl)-N-acetyl-D-glucosamine + H2O Eliminative cleavage of (1->4)-beta-D-glucuronans to give oligosaccharides with 4-deoxy-beta-D-gluc-4-enuronosyl groups at their non-reducing ends. Complete degradation of glucuronans results in the formation of tetrasaccharides. Is inhibited by mono- and divalent cations as well as L-ascorbic acid 6-hexadecanoate. Vmax for poly-GlcA is about 10-fold greater versus poly-ManA or HA (PubMed:24257754). kcat is 31.9 sec(-1) with poly-GlcA as substrate (at pH 7) (PubMed:24808176). kcat is 3.3 sec(-1) with poly-ManA as substrate (at pH 9) (PubMed:24808176). Optimum pH for enzymatic activity is substrate-dependent, with optimal hyaluronate degradation at pH 5, poly-beta-D-glucuronate degradation at pH 7, and alginate degradation at pH 9. Belongs to the polysaccharide lyase 5 family.