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BACKGROUND Oxidation has been reported as the one of the deterioration reactions of proteins in aquatic products. Searching for new bioacitve substances from marine algae has been one of the main areas in food science and additives. RESULTS In this study, a novel protein was determined after ammonium sulfate precipitation and gel filtration chromatography from red algae Porphyra haitanensis. It had closely corresponded with the antioxidant activity and was identified as an uncharacterized protein with molecular mass of 43 kDa, designated Ph43. Bioinformatic analysis revealed that Ph43 is a novel protein of non-phycobiliprotein family with putative CHRD domains and riched in α-helical conformation. Recombinant protein (rPh43) was expressed in Escherichia coli as a Hig-tagged protein using a pET-22b vector system and purified by the affinity HPLC. Spectroscopy analysis revealed that there's no structural differences between rPh43 and natural recovered Ph43. Moreover, the rPh43 showed equal/higher antioxidant activity compared with Ph43. rPh43 has the potential to be applied as natural antioxidants for food stabilization. CONCLUSION Our results identified a novel antioxidant protein with molecular mass of 43 kDa derived from Porphyra haitanensis that belongs to the non-phycobiliprotein family. This article is protected by copyright. All rights reserved.