FUNGAL HEMICELLULASE

Description

The most abundant carbohydrate in nature is cellulose, the principal structural material of plants. Cellulose is a water insoluble P-(l-4) linkage. Cotton is almost pure cellulose, whereas structural parts of plants - wood, straw, stalks, etc. - contain about 50% cellulose. In these plant structural materials the cellulose is bound together by lignin, and there are also present varying amounts of other carbohydrates, hexosans and pentosans besides cellulose. These other carbohydrate polymers associated with cellulose in nature are of ill-defined composition and may be classified as hemicelluloses. These occur in almost all plant tissues - wood, straw, stalks, hulls, seeds, etc. - in relatively low to relatively high concentrations. Some, the gums, are water-soluble or dispersible; others are insoluble. Mannose, galactose, xylose and arabinose are the most common sugars found in the various hemicelluloses, but other sugars also often occur. Frequently more than one kind of sugar is present in common hemicelluloses. For example, the principal component of guar gum is a complex galactomannan. Cellulosic materials are degraded in nature by certain microorganisms. These microorganisms obviously produce enzymes that have long been sought because of the availability of huge amounts of cellulosic plant wastes as potential sources for glucose of chemical and food industries, the interest by food technologists in upgrading fibrous food products, and the potential as a digestive aid for man and animals and in waste disposal systems.
The cellulases may be divided into two major type, the C,-type enzymes which act on native cellulose giving linear, insoluble glucose chains and the Cx enzymes which act upon these or swollen or ground cotton, carboxymethyl cellulose or cellulodextrins to produce soluble, low molecular weight products. Included in theCx enzymes are various fractions which differ significantly in pH optima and temperature stability. Some of these fractions are endoenzymes and act in a random manner, and some are exoenzymes.