26 MICROBIAL CELL WALLS 



polysaccharide from the latter appears to be more highly 

 branched.^' -'^'^ Some differences in the linkages and degree 

 of branching have been suggested for mannans derived 

 from various yeasts.^' °'^ 



Isolation of walls by mechanical disintegration led to the 

 discovery of protein and lipid components in addition to 

 the polysaccharides. ''^'^'^° Not all yeast species contain 

 appreciable quantities of lipid in the wall, for Kessler and 

 Nickerson^ found as little as 1% total lipid in the walls 

 of strains of Candida albicans and as much as 10% in the 

 wall of Saccharomyces cerevisiae. A clearer understanding 

 of the molecular architecture of the yeast cell wall has 

 begun to emerge from the important discovery by Falcone 

 and Nickerson ^ that the wall polysaccharides occur as 

 protein complexes. Further investigations by Kessler and 

 Nickerson ^ have established the presence of a glucan-pro- 

 tein complex and two types of glucomannan-protein com- 

 plexes in a variety of yeast walls. The percentage of the 

 wall accounted for by the various polysaccharide-protein 

 complexes for several yeasts is illustrated in Table 8. The 

 presence of a mannan-protein complex in baker's yeast wall 

 has been confirmed by Korn and Northcote/^ and, from 

 alterations in the surface charge of yeast walls degraded 

 with various enzymes, Eddy ^^ has suggested that the man- 

 nan-protein complex forms part of the outside layer of 

 the wall. However, this suggestion, based on microelectro- 

 phoresis data, must await more definitive biochemical and 

 chemical investigations. The nature of the bonding be- 

 tween the polysaccaride-protein complexes is not known, 

 but Kessler and Nickerson ^ suggest the possibility of esterifi- 

 cation of carboxyl groups of the protein with hydroxyl 

 groups of the polysaccharides. 



