Catalyzes the depolymerization of alginate through an exolytic mode of action, via a beta-elimination mechanism. Preferentially acts on oligoalginates with degrees of polymerization higher than 2 to produce the alginate monomer, 4-deoxy-L-erythro-5-hexoseulose uronic acid. Cleavage of 4-deoxy-alpha-L-erythro-hex-4-enopyranuronoside oligosaccharides into 4-deoxy-alpha-L-erythro-hex-4-enopyranuronate monosaccharides. The zinc ion seen in the crystal structure is located far away from the active site and likely plays a structural role. However, it seems important for enzyme activity since the mutation of one of its coordination residues causes a high decrease in activity. kcat is 56.9 sec(-1) with low viscosity alginate as substrate. kcat is 62.4 sec(-1) with alginate trisaccharide as substrate (at pH 7.5 and 30 degrees Celsius). Optimum pH is 6. Optimum temperature is 40 degrees Celsius. Homodimer. Could be used as the key enzyme to produce alginate monomers in the process of utilizing alginate for biofuels and chemicals production. Belongs to the polysaccharide lyase 17 family.