Alginate lyases from alginate-degrading Vibrio splendidus 12B01 are endolytic

Alginate lyases are enzymes that degrade alginate through β-elimination of the glycosidic bond into smaller oligomers. We investigated the alginate lyases from Vibrio splendidus 12B01, a marine bacterioplankton species that can grow on alginate as its sole carbon source. We identified, purified, and characterized four polysaccharide lyase family 7 alginates lyases, AlyA, AlyB, AlyD, and AlyE, from V. splendidus 12B01. The four lyases were found to have optimal activity between pH 7.5 and 8.5 and at 20 to 25°C, consistent with their use in a marine environment. AlyA, AlyB, AlyD, and AlyE were found to exhibit a turnover number (k_cat) for alginate of 0.60±0.02 s^-1, 3.7±0.3 s^-1, 4.5±0.5 s^-1, and 7.1±0.2 s^-1, respectively. The K_m values of AlyA, AlyB, AlyD, and AlyE toward alginate were 36±7 μM, 22±5 μM, 60±2 μM, and 123±6 μM, respectively. AlyA and AlyB were found principally to cleave the β-1,4 bonds between β-D-mannuronate and α-L-guluronate and subunits; AlyD and AlyE were found to principally cleave the α-1,4 bonds involving α-L-guluronate subunits. The four alginate lyases degrade alginate into longer chains of oligomers.