Hypnins, low-molecular weight peptidic agglutinins isolated from a marine red alga, Hypnea japonica

Abstract

Four electrophoretically homogeneous agglutinins have been isolated from the aqueous ethanolic extract of the marine red alga Hypnea japonica by precipitation with organic solvents, gel filtration, and reversed-phase and gel permeation high-performance liquid chromatography. Since these agglutinins were found to be new peptides, they were designated hypnins A, B, C and D after the generic name of the seaweed. The major agglutinin, hypnin A, was a monomeric peptide with a molecular weight of 4200. It had an isoelectric point of 4.3, and contained large amounts of serine and glycine. The N- and C-terminal amino acids were identified as tyrosine and serine, respectively. On the other hand, hypnins B and C were suggested to be dimeric or trimeric forms of hypnin A or the related peptide, while hypnin D was quite different from the others. Hypnin A agglutinated not only animal erythrocytes other than human, but also mouse FM3A tumour cells. The hemagglutinating activity was inhibited only by glycoproteins with N-glycosidic sugar chains of a complex type. The hemagglutinating activity of hypnin A was not affected by heating for 30 min at 100°C or by addition of divalent cations. Hypnins B, C and D were similar to hypnin A in hemagglutination pattern and sugar-binding specificity.