Isolation and identification of a novel algicidal peptide from mackerel muscle hydrolysate

To help remedy damage from harmful algal blooms, an attempt was made to isolate an algicidal substance previously observed to be present in mackerel muscle hydrolysate. Crude extract was obtained by cold acetone precipitation, and it dissolved best in water. Through molecular weight cut-off determination and tricine-SDS PAGE, the algicidal substance was determined to be a peptide of < 1 kDa. Based on this result, purification was first performed using size exclusion chromatography and preparative reverse phase high-performance liquid chromatography. Then, the active algicidal fraction was applied to an ultra-performance liquid chromatography-electrospray ionization-mass spectrometry system, followed by MS/MS analysis. The algicidal peptide had linear structure consisting of amino acids with sequence NH-KMNF-COOH. Its calculated properties were: molecular weight 538.66 g/mol; isoelectric point 9.91; net charge + 1 at pH 7.0; and 50% hydrophobicity. Algicidal ability of the identified peptide was confirmed using synthesized peptide. The LC50 values toward four harmful algal blooming species were 0.69, 0.83, 0.85 and 1.24 mg/ml for Alexandrium fundyense, A. catenella, Heterocapsa triquetra, and Prorocentrum minimum, respectively. There was no coincidence in the sequence of the identified peptide with those of known metabolites in the APD, Norine, CAMP, UniProt and METLIN databases. Consequently, this algicidal substance originating from mackerel protein was deduced to be a novel peptide that can usefully be applied to relieve harmful algal blooms.