Illexins A, B, and C from squid ink should have a branched structure

Illexin A, illexin B, and illexin C, isolated from ink of the squid Illex argentinus, have been reported to have a structure consisting of linear repeating units of (-6GalNAc alpha 1-3GlcA beta 1-3Fuc alpha 1-)n [Biochem. Biophys. Res. Commun. 198, 560 (1994)]. This structure was further investigated using NOESY and atmospheric pressure MS/MS measurement of PA-trisaccharide obtained by acid hydrolysis of illexin C. The results indicated that the structure is, in fact, branched. Observation of both [GalNAc-Fuc-PA]- and [GlcA-Fuc-PA]+ obtained as product ions from the molecular ion of PA-trisaccharide on the MS/ MS spectra suggested a branched repeating unit. NOEs between H-1 of GalNAc and H-3 of Fuc, and between H-1 of GlcA and H-4 of Fuc, revealed the positions of glycosidic linkages, and from the results of sodium periodate oxidation of illexin C and PA-trisaccharide, the structure was determined to be (-3GlcA beta 1-4(GalNAc alpha 1-3)Fuc alpha 1-)n.