A gene, alg7D, from Saccharophagus degradans, coding for a putative alginate lyase belonging to the family of polysaccharide lyase-7, was overexpressed in Escherichia coli. The properties of the recombinant Alg7D were characterized. The enzyme endolytically depolymerized alginate by beta-elimination into oligo-alginates with degrees of polymerization of 2-5. Its activity was maximal at 50A degrees C and pH 7 and was slightly increased in the presence of Na+. The K (M) , V (max) , k (cat) , and k (cat) /K (M) values were: 3 mg ml(-1), 6.2 U mg(-1), 1.9 x 10(-2) s(-1), and 6.3 x 10(-3) mg(-1) ml s(-1), respectively.