Ulvan lyases can degrade ulvan to oligosaccharides with potent biological activity. A new ulvan lyase gene, ALT3695, was identified in Alteromonas sp. A321. Soluble expression of ALT3695 was achieved in Escherichia coli BL21 (DE3). The 1314-bp gene encoded a protein with 437 amino acid residues. The amino acid sequence of ALT3695 exhibited low sequence identity with polysaccharide lyase family 25 (PL25) ulvan lyases from Pseudoalteromonas sp. PLSV (64.14% identity), Alteromonas sp. LOR (62.68% identity), and Nonlabens ulvanivorans PLR (57.37% identity). Recombinant ALT3695 was purified and the apparent molecular weight was about 53 kDa, which is different from that of other polysaccharide-degrading enzymes identified in Alteromonas sp. A321. ALT3695 exhibited maximal activity in 50 mM Tris-HCl buffer at pH 8.0 and 50 °C. ALT3695 was relatively thermostable, as 90% activity was observed after incubation at 40 °C for 3 h. The Km and Vmax values of ALT3695 towards ulvan were 0.43 mg·mL−1 and 0.11 μmol·min−1·mL−1, respectively. ESI-MS analysis showed that enzymatic products were mainly disaccharides and tetrasaccharides. This study reports a new PL25 family ulvan lyase, ALT3695, with properties that suggest its great potential for the preparation of ulvan oligosaccharides.

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