Characterization and properties of the phosphomannan from Hansenula hostii NRRL Y-2448

Abstract

The phosphorylated mannan produced in good yield from glucose by the bisexual diploid yeast, Hansenula holstii NRRL Y-2448, appears to be the first significantly phosphorylated polysaccharide to be obtained from a yeast or a nonpathogen. Isolated as the potassium salt, this water-soluble polysaccharide derivative has constituents in the proportion, d-mannose:phosphorus:potassium::5:1:1. The product has [ α] D 25 + 103 ° (in 0.1 M potassium chloride), M N (reducing power) 103,000 ± 10,000, M W (light scattering) of the order of 16 × 10 6, S 20, w = 44, and an unusually homogeneous molecular distribution for an unfractionated, native polymer. The single titration equivalence-point of the polyacid at pH 7.2 indicates a phosphodiester structure. Weak acid liberates secondary hydrogen ions and causes molecular degradation; dilute alkali appears to cause no structural change. Aqueous solutions show exceptional resistance to microbial attack. The brilliantly clear aqueous solutions have properties characteristic of a plastic, thixotropic, polyelectrolyte. The viscosity-concentration curve shows a viscosity maximum of 2500 cp. at 1.5% polysaccharide concentration and a minimum of 1700 cp. at 3%. At suitable concentrations of phosphomannan and borax, complexing and cross-linking occur; the presence of potassium chloride augments these effects.