A-D-Mannan

Benzyl derivatives of (1 6)-a-D-glucan, (l->6)-a-D-mannan, and (l-> 6)-a-D-galactan have been studied in 1,4-dioxane. These derivatives have complex and interesting c.d. spectra due to the ww transition of the chromophore with resolved vibrational structure. However, a conformational interpretation of these interesting spectra is not possible at this time. 

The structures of the cell-wall D-mannans of several other yeasts have been investigated381 by use of this exo-a-D-mannanase. Five were degraded to the (l->6)-a-D-mannan chain. Those which contained jB-linked d-mannosyl units or a-D-galactosyl groups in the side chains were not significantly hydrolyzed. However, removal, by partial hydrolysis with acid, of the a-D-galactosyl units from five galactomannans, and of /3-linked D-mannosyl units from three other D-mannans, rendered these polysaccharides partially susceptible to hydrolysis by exo-a-D-mannanase, consistent with an a-linked-D-mannan structure. 

Invertase from a Saccharomyces cerevisiae mutant could be separated into two fractions on the basis of solubility in ammonium sulfate.382 The soluble fraction reacted with endo-(l - 6)-a-mannanase, when it became insoluble. The results suggested that the insoluble fraction contained only the highly branched, core section, but the soluble fraction also had the (l->6)-a-D-mannan chain attached. 

A D-mannan was obtained from the kernel of the African doum palm (Hyphaene thebaica).119 a-D-Mannans having glucose as aminor componenthave been isolated from the lichen Tornabenia intricata.120... 

The general molecular structure of yeast exocellular mannoproteins is similar to that of mannoproteins in the cell wall (Volume 1, Section 1.2) (Villetaz et al., 1980 Llauberes et al., 1987 Llauberes, 1988). It consists of a peptide chain connected to short side chains made up of four maunose units and a high molecular weight, branched a-D-mannane (Figure 3.24). 

Table IV lists those yeasts (other than the aforementioned Sporobolomyces sp.) that synthesize polysaccharide-like 0 -phos-phonoglycans along with the various a-g-glycose 1-phosphate end groups found thus far (50). A new aspect of the phosphomannan story is introduced in this table When grown in the absence of added orthophosphate, almost all such yeasts alternatively synthesize neutral a-D-mannans and glucoraannans. Common biogenetic origin of the neutral and phosphorylated mannans and glucomannans is evidenced by similar amounts of g-glucose or its absence in the biopolymers produced by a given strain of yeast.

Methylation analysis and enzymic degradation studies established the presence of a structure (23) containing short side-chains of (1 -> 2)-at-D-mannosyl residues attached to a main backbone of (1 6)-ot-D-mannopyranosyl residues. In addition, a serologically inactive a-D-mannan whose structure (24) resembles that of the core L-arabino-D-mannan has been isolated. 

A glycoprotein which has been isolated from the cell walls of baker s yeast was shown to be a D-mannan-protein complex. After immobilization by covalent attachment to macroporous agarose, this was used in the purification of an a-D-mannosidase from jack-bean meal. 

The synthesis of a D-glucan by C. guilliermondii was inhibited by diphenylamine, which, at the same time, stimulated the synthesis of a D-mannan. ... 

Various strains of yeasts that produce characteristic phosphono-D-mannans also synthesize characteristic extracellular a-D-mannans, which appear to differ in the degree of branching and in the type of glycosidic linkages. Methylation analysis showed that the mannans contain a fl 6)-linked a-D-mannosyl backbone, to which (1 3)-linked [e.g. (19) in Pichia mucosa] or (1 3)- and/or... 

Selective radio-labelling of the cell-wall o-mannan in growing S. cerevisiae showed that it is not metabolized during exponential growth, since, once inserted into the wall, it is not subject to turnover or release into the growth medium. A D-mannan that was isolated from the growth medium is either non-structural or synthesized de novo, but not trapped in the structure of the growing cell wall. 

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