Molecular Size Analysis ofHaemophilus Influenzae Type B Capsular Polysaccharide

Abstract

The molar mass and molar mass distribution of polyribosyl ribitol phosphate (PRP) was determined using high performance size-exclusion chromatography with light scattering, viscometric, and refractive index detection. Light scattering data showed the PRP preparations to have an M_w of ca. 75,000, and a polydispersity (M_w/M_n) of about 1.46. Based on integration of the molar mass and intrinsic viscosity data, the Mark-Houwink-Sakurada coefficients for PRP were determined to be a = 1.45, and K = 3.57×10⁻⁶ cm³/g for 0.2 M ammonium acetate, pH 7.0, and a = 1.54 and K= 0.6×10⁻⁶ cm³/g for 0.1 M sodium phosphate, pH 7.2. The values of a indicate that PRP is a rigid, rod-like molecule. The rigidity of the PRP molecules is characterized by unperturbed dimensions (<R_o>/M^1/2) of 0.24 nm in ammonium acetate buffer and 0.22 nm in sodium phosphate buffer. These results suggest that PRP likely has a highly ordered secondary structure.