Ulvan lyase involved in ulvan degradation. 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 the endolytic cleavage of the glycosidic bond between Rha3S and the uronic acids GlcA or IduA, producing oligosaccharides that have unsaturated 4-deoxy-L-threo-hex-4-enopyranosiduronic acid (deltaUA) at the non-reducing end. This results eventually in the degradation of the ulvan polysaccharide into deltaUA-Rha3S disaccharides and deltaUA-Rha3S-Xyl-Rha3S tetrasaccharides