Abstract
Nidamental glands of the squid Illex argentinus contain mucosubstance which forms jelly-like egg masses after spawning. In this study, a sulfated glycoprotein was prepared from the mucosubstance by solubilization with mild alkaline treatment (0.4 N NaOH, 4°C, 4h), followed by precipitation with ethanol (50%), and was characterized with respect to its chemical composition and macromolecular properties. The glycoprotein accounted for about 35% of the mucosubstance by weight and comprised 22.6% protein, 73.0% carbohydrate, and 4.4% ester sulfate. A large part of the glycoprotein was isolated after actinase digestion as a long, asymmetric, protease-resistant fragment having a molecular mass of about 1400 kDa. The protein backbone of the fragment accounted for 18.7% by weight and was composed virtually of Thr, Pro, and Ile in the molar ratio of 2:1:1. All Thr residues, comprising 45% of the total amino acids, were considered to link to GalNAc residues of oligosaccharides consisting mainly of Gal, Fuc, GalNAc, and an unidentified amino sugar. These combined results strongly suggest that the sulfated glycoprotein is heavily O-glycosylated and defined as a mucin. The Thr-GalNAc linkages, however, were resistant to β-elimination (0.5 N NaOH, 25°C, 24h). The mucin molecules were assumed to be mainly responsible for the viscous and gel-forming properties of the nidamental gland mucosubstance.
