INTERCELLULAR SUBSTANCES AND WALLS 81 



Although the chitin of intact walls commonly gives a somewhat 

 modified diffraction pattern, simple preparative procedures have 

 been used quite successfully to demonstrate its presence. The 

 sporangiophores of Phycomyces (phycomycete) and Aspergillus 

 (ascomycete) have been shown to contain a typical a-chitin. 

 Crystallographically, the unit cell of a-chitin in fungi, as in animals 

 is rhombic, 9.4 > 10.46 > 19.25 A in dimensions, and contains 

 8 N-acetylglucosamine residues. The sugar residues are present 

 as the disaccharide chitobiose, the analog of cellobiose in the 

 cellulose molecule. The four chitin chains they represent are further 

 arranged in two antiparallel sets, precisely the situation in cellulose. 

 The fiber period corresponds to two glucopyranose lengths, as 

 in the case of cellulose. Chitinous walls exhibit the lammelar 

 and fibrillar organization typical of cellulosic walls. Physical ana- 

 lysis (electron microscopy, polarized light) of the Phycomyces 

 sporangiophore shows that it consists of an outer primary wall 

 of tubular texture, a thickened secondary wall of fibous texture 

 and a very thin inner core of steeply spiraled texture. Thus, both 

 spiral and stratiform structural plans are present. The Aspergil- 

 lus sporangiophore exhibits spiral texture. Although supporting 

 chemical data have been applied in such studies the burden 

 of proof has been served by the physical methods of analysis. 



The constitution of the yeast cell wall has been elucidated 

 mainly by chromatographic and other chemical procedures sup- 

 ported by physical methods such as differential centrifugation and 

 electron microscopy. These combined methods show that the 

 yeast cell wall which makes up about 15 per cent of dry cell contains: 



lipid hexosamine 



glucose amino acids 

 mannose 



Glucose is present in part as a highly branched insoluble polymer 

 whose molecular weight is about 6,000,000. The interbranch dis- 

 tance corresponds to nine glucopyranose units joined in 1,3-link- 

 ages; the branch points are joined by l,2,linkages. This material 

 in association with protein makes up about 30 per cent of the 

 cell wall. The rest of the glucose appears in two soluble components, 



