Unsaturated beta-glucuronyl hydrolase involved in ulvan degradation (Ref.2, PubMed:31285597). 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) (Probable). Unsaturated 3S-rhamnoglycuronyl hydrolase works together with ulvan lyases to fully degrade the ulvan polymer, catalyzing specifically the cleavage of the unsaturated 4-deoxy-L-threo-hex-4-enopyranosiduronic acid (deltaUA) of deltaUA-Rha3S disaccharides and deltaUA-Rha3S-Xyl-Rha3S tetrasaccharides, the end products of the ulvan lyase reaction. Also hydrolases deltaUA-Rha3S-IduA-Rha3S and deltaUA-Rha3S-GlcA-Rha3S tetrasaccharidestetrasaccharides. Prefers tetrasaccharides over disaccharides and prefers an uronic residue at subsite +2 (By similarity). By ulvan and rhamnose. Belongs to the glycosyl hydrolase 105 family.