Optical polarization reveals different ultrastructural molecular arrangement of polysaccharides in the yeast cell walls.

The topo-optical aldehyde bisulfite-toluidine blue (ABT) reaction of vicinal OH and amino-OH groups offers new ways to study the ultrastructure of polysaccharides in different biological substrates. Through oriented dye binding on the reacting groups, the ABT reaction induces strong birefringence on the linearly ordered polysaccharides, which is negative with respect to their chain length. Using this method, two types of molecular order of the polysaccharides could be distinguished in the cell walls and capsules of yeasts. (1) The optically negative spherulitic character of the yeasts after the ABT reaction indicated that the toluidine blue molecules were bound tangentially (in a surface-parallel pattern) while the polysaccharide chains of the cell walls and capsules were oriented mainly radially. This structural pattern may be explained as resulting from a helicoid conformation of the polysaccharide component. (2) Acid or alkali hydrolysis removed the radially oriented polysaccharide component of the cell wall. The remaining, resistant polysaccharides showed up in the form of optically positive spherulites indicating radially oriented dye molecules on a circularly ordered, micellar polysaccharide texture.