Caesium chloride isopycnic density-gradient ultra-centrifugation of the material eluted in the Vi of the gel filtration column. Freeze-dried material eluted in the Vi was dissolved in 4 M GuHCl containing 10 mM EDTA, 5 mM NEM and 0.05% CHAPS pH 6.5 and adjusted to a density of 1.39 to 1.40 g/ml with caesium chloride. Density gradient centrifugation was performed in a Beckman L45 ultra-centrifuge for 48 h at 105 000 g at 4°C. Fractions with high PAS (◆) and low protein (Lowry) (■) (a) were pooled and adjust to a density of 1.39 to 1.40 g/ml with caesium chloride for a second step centrifugation (b). Mucin rich fractions with a density (▲) between 1.37–1.42 were pooled, dialysed against three changes of distilled water for overnight at 4°C and freeze-dried.