Ulvan lyase involved in ulvan degradation (PubMed:28958183). Ulvan is the main polysaccharide component of the Ulvales (green seaweed) cell wall. It is composed of disaccharide building blocks comprising 3-sulfated rhamnose (Rha3S) linked to D-glucuronic acid (GlcA), L-iduronic acid (IduA), or D-xylose (Xyl). Ulvan lyase catalyzes preferentially the endolytic cleavage of the glycosidic bond between Rha3S and the uronic acid GlcA, but not IduA, producing oligosaccharides that have unsaturated 4-deoxy-L-threo-hex-4-enopyranosiduronic acid (deltaUA) at the non-reducing end. The most abundant end products in the degradation of the ulvan polysaccharide were deltaUA-Rha3S disaccharides and deltaUA-Rha3S-IduA-Rha3S and deltaUA-Rha3S-Xyl-Rha3S tetrasaccharides (By similarity). By ulvan (at protein level). Belongs to the polysaccharide lyase 24 family.