Immunochemical Approaches to the Structural Chemistry of Polysaccharides

Based on quantitative precipitin theory, it is possible to identify some sugar groupings in a polysaccharide molecule by immunochemical cross-reactions. The structural features of some type-specific pneumococcal polysaccharides are shown and the reasons for their cross-reactions in different antipneumococcal sera are discussed. Verification of these conclusions was made by studying the cross-reactions of different polysaccharides having similar sugar grouping, in these sera. Hualtaco and mangle gums precipitated antibodies in different antipneumococcal sera and the reasons for this are discussed from the structural point of view. Immunochemical methods are also of great help in establishing the homogeneity of a polysaccharide. Some limitations to the use of this method for identifying the sugar residues in a polysaccharide molecule are also indicated. One of them could be explained on the basis of stereochemical identity of some monosaccharide units, as in the case of 3-O-methyl-D-galactose and L-fucose. The largest dimensions of antibody combining sites are complementary to those of an oligosaccharide containing six hexopyranose units. Studies on the size and shape of this molecule will help in making the inhibition technique more widely applicable. Immunochemical methods are becoming more useful in structural polysaccharide chemistry. Polysaccharides are the third largest group of biopolymers; they have attracted the attention of chemists for more than a century. Structural elucidations of these substances are challenging problems to organic chemists, and a major break-through was achieved with Haworth's methods of methylation. Oxidation by periodate, Barry and Smith degradation and graded hydrolysis are some of the well-known methods used to interpret the structural details of these macromolecules'. Spectral methods2 have recently been utilized for characterizing the small fragments isolated from various derivatives of polysaccharides. Aspects such as size and shape have not been studied using physicochemical methods, except in a few cases such as cellulose and starch, although this problem is important in understanding the behaviour of these molecules in solution. The three-dimensional structure of monosaccharide molecules can be ascertained by x-ray crystallography. Indeed, substantial progress has been made in the structural elucidation of polysaccharides but much remains to be understood. This is mainly due to the polyfunctional nature of the monosaccharide units in the polymer;