The microcyst wall of Didymium iridis: chemical analyses

Chemical analyses of the microcyst cell wall of Didymium iridis were done to compare it with other well-studied organisms, Physarum polycephalum and Physarum flavicomum. Large wall fragments were obtained by breakage in a Braun homogenizer. Chemical analyses of purified walls identified neutral sugars, protein, and hexosamine as the major components. Wall polysaccharides were mostly composed of galactosamine with smaller amounts of glucose and galactose. The protein component consisted of large quantities of threonine and aspartate–asparagine with trace amounts of the sulfur-containing amino acids. Most of the wall protein was soluble in alkaline urea. Sodium dodecyl sulfate – polyacrylamide gel electrophoresis was used to identify seven major bands, at least four of which are acidic glycoproteins. Most of the galactosamine was associated with the urea – hot alkali insoluble fraction comprised mostly of glucose. This galactosaminoglucan was partially sulfated and acetylated and arranged as microfibrils that maintain cell shape.