Abstract
Unsaturated alginate disaccharides (UADs), enzymatically derived from the degradation of alginate polymers, are considered powerful antioxidants. In this study, a new high UAD-producing alginate lyase, AlySY08, has been purified from the marine bacterium Vibrio sp. SY08. AlySY08, with a molecular weight of about 33 kDa and a specific activity of 1070.2 U/mg, showed the highest activity at 40 °C in phosphate buffer at pH 7.6. The enzyme was stable over a broad pH range (6.0–9.0) and retained about 75% activity after incubation at 40 °C for 2 h. Moreover, the enzyme was active in the absence of salt ions and its activity was enhanced by the addition of NaCl and KCl. AlySY08 resulted in an endo-type alginate lyase that degrades both polyM and polyG blocks, yielding UADs as the main product (81.4% of total products). All these features made AlySY08 a promising candidate for industrial applications in the production of antioxidants from alginate polysaccharides.
Highlights
Alginate is a linear hetero-polyuronic acid polymer, composed of β-D-mannuronate (M) and its C5 epimer α-L-guluronate (G), which can be arranged as polyM blocks, polyG blocks, and alternating or random polyMG blocks [1,2,3]
Alginate lyases catalyze the depolymerization of alginate through a β-elimination reaction between uronic acids in the linear polymer, producing unsaturated alginate oligosaccharides (UAOs) with double bonds between C4 and C5 at the non-reducing ends [7,8]
Unsaturated alginate disaccharides (UADs) are generally full‐length alginate lyase, AlyL2‐FL, is able to produce a high ratio of UADs (64.6% of the total present in low proportions in the products of most alginate lyases, except product), the activity strictly depends on the NaCl concentration [22]
Summary
Alginate is a linear hetero-polyuronic acid polymer, composed of β-D-mannuronate (M) and its C5 epimer α-L-guluronate (G), which can be arranged as polyM blocks, polyG blocks, and alternating or random polyMG blocks [1,2,3]. It is the most abundant carbohydrate in brown algae and approximately. UAOs are endowed with an excellent antioxidant activity, superior to ascorbic acid in lipid oxidation treatment [9,10] Their antioxidant activity is dependent on the conjugated alkene acid structure occurring in UAOs from the enzymatic depolymerization of alginate [9]. The antioxidant activity is inversely related to the molecular weight of UAOs: the smaller the size of the UAOs, the higher the antioxidant activity [14]
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