Glucan microfibrillarity

These polymers are distinguished from cellulose by the presence of both/ -(l— 3)- and / -(l— 4)-linked D-glucosyl residues, lower molecular weights (some noncellulosic glucans are water-soluble), and susceptibility to hydrolysis by / -D-glucanases that cannot hydrolyze cellulose. Unlike cellulose, whose microfibrillar structure and structural role in the cell wall has been clearly established, the function of these polymers as structural components of the wall is still a subject of controversy there is some evidence that they are energy-reserve materials.110-201 202... 

Since three of the major wall components are potentially water soluble, the effective removal or weakening of the cell wall must involve enzymatic hydrolysis of the long chains of / -(1 - 3)-linked glucose residues in the microfibrillar, alkali-insoluble glucan layer. In some species of yeast an additional structural wall component occurs, which has been identified as a linear -( —> 3)-glucan. 

The enormous interest in augmenting the world s supply of protein from microbial sources (135) has focussed much attention on this source of protein as a nutrient for animals as well as humans. However, there is some evidence that if intact yeast cells are included in a diet, the tough polysaccharide-containing cell wall may constitute at least a partial barrier in the effective utilization of the protein of the cytoplasm. One reason for this is the absence of enzymes in the digestive tract of humans and most warm-blooded animals capable of hydrolyzing the microfibrillar / -glucan component of the cell wall (135,136). Other factors may include the inability of the proteolytic enzymes of the digestive track to make effective contact with the cells protein. 

Hyphal walls are usually two layered with an inner layer of microfibrillar materials, usually chltln or cellulose, or both and an outer layer of amorphous glucan. The chltln Is composed of... 

Bulone V., Fincher G.B., and Stone BA. 1995. In vitro synthesis of a microfibrillar (1 3)-P-glucan by a ryegrass Lolium multijlorum) endosperm (l- 3)-P-glucan synthase enriched by product entrapment. Plant J 8 213-225. 

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