Saccharomyces cerevisiae glucan

Fig. (4). C-NMR spectrum of Saccharomyces cerevisiae glucan. (Solvent DMSO-dg, temperature 28 °C, chemical shifts expressed relative to tetramethylsilane). Reproduced from [22].

Intrinsic (natural, innate) resistance. In one form of intrinsic resistance, the fungal cell wall (see Chapter 2) is considered to present a barrier to exclude or, more likely, to reduce the penetration by biocide molecules. The evidence to date is sketchy but the available information tentatively links cell wall glucan, wall thickness and consequent relative porosity to the sensitivity of Saccharomyces cerevisiae to chlorhexidine. 

Simultaneous saccharification and fermentation (SSF) experiments were conducted according to NREL standard protocol (LAP-008). Each SSF flask was loaded with 3% (w/w) glucan, 1% (w/v) yeast extract, 2% (w/v) peptone, 0.05 M citrate buffer (pH 4.8), the appropriate amount of cellulase enzyme to achieve 15 FPU/g of glucan, and the appropriate amount of Saccharomyces cerevisiae DSA (provided by NREL) inoculum (starting optical density of 0.5). The SSF flasks were equipped with water traps to maintain anaerobic conditions and were incubated at 37°C with gentle rotation (130 rpm) for a period of 168 h. 

Cell walls of Saccharomyces cerevisiae were found to contain a (1— 6)-linked j8-D-glucopyranan this was isolated, and identified by i.r. spectroscopy52 and chemical-analysis techniques.53 The alkali-in-soluble glucan from S. cerevisiae contains this and a (1— 3)-linked /3-d-glucopyranan in the ratio54 of 1 5.7. The former, of mol. wt. 2 x 105, has 6-0- and 3-O-substituted units in the ratio of 4.4 1, and contains 14% of 3,6-di-O-substituted units.55 (A similar heterogeneity occurred... 

The main structural constituents of Saccharomyces cerevisiae yeast cell wall are glucans and mannans with a minor proportion of chitin (Walker 1998). Manno-proteins are located in the outer layer of the yeast cell wall and determine most of the surface properties of the wall. Vasserot et al. (1997) studied the capacity of yeast lees to adsorb anthocyanins in an attempt to reduce the detrimental effects of charcoal on the color of red musts and wines. Experiments based on model wine solutions revealed that yeast lees possess a greater affinity for anthocyanins than... 

The cell wall of Saccharomyces cerevisiae has a structure of crossed molecules of /3-D-linked D-glucan, which gives the wall its strength and the cell its shape. This glucan is embedded in other polysaccharide(s) or in glycoprotein. Thus, yeast cell-walls consist mainly of polysaccharide, with relatively little protein, lipid, or min-... 

Investigation of a partially purified particulate gluean preparation from Saccharomyces cerevisiae cell walls has expanded. Glucan is held re-sponsil le for most of the reticuloendothelial-stimulating properties of zymosan. The preparation was reported to activate macrophages as assessed by... 

A historical review of the development of our knowledge of the yeast cell wall was given by Phaff (I). Most information based on chemical studies has been derived, by far, from studies with cell walls from baker s yeast, Saccharomyces cerevisiae, and closely related species. The principal components of Saccharomyces walls are several types of glucan and a mannan-protein complex which may contain variable proportions of phosphate. A low content of chitin (ca. 1% ) may be present depending on the number of times a cell has produced buds. The reason for this is that chitin is present only in the bud scars (ca. 3 pm2 in area) produced on the surface of a mother cell (2), each at a different place on the cell surface. 

Figure 1. Possible structures for alkali-insoluble ft-glucan from the cell wall of Saccharomyces cerevisiae after Manners et al. (3). Part A represents a comb-type structure, while part B represents a tree-type structure. In the former, most or all of the glucose residues comprising the backbone are thought to carry side chains with an average of ca. 30 glucose residues (two side chains shown). In the latter, a + b -f c comprise ca. 60 glucose residues. See text for further details.

It is also clear from studies in recent years that there is no universal process by which the alkali-insoluble glucan of Saccharomyces cerevisiae or other species can be hydrolyzed enzymatically. Among the lytic / -glucanases the following action patterns have been identified (a) endo-/ - (1 3) -glucanases causing random hydrolysis of -(1 - 3)-glucans... 

Chitin is almost always found as crystalline microfibrils usually embedded in a matrix constituted of other polysaccharides. For example, in Saccharomyces cerevisiae(19), chitin is found in the form of microfibrils along with fibrilar (1-+3)-6-D-gl ucan. The latter is also found in other species as a matrix polysaccharide embedding the chitin microfibrils as in Schizophyl1 urn commune.(31) This composite material is also associated with (l>TJ-3-D-glucan to constitute the final cell wal1. 

Cell-wall formation in Saccharomyces cerevisiae appears to be the result of two main patterns of deposition of wall material, viz., around the whole periphery of the non-budding cells and mainly at the tip of the daughter cell, or at the cross-wall that separates dividing cells. Synthesis and secretion of j3-D-glucan is unaffected by inhibition of RNA and protein synthesis. Growth of S. cerevisiae under conditions of phosphate limitations results in a decreased content of D-glucan and increased protein content as compared with control cells. 

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