Disaccharide sources

D (+) Galactose is a constituent of numerous polysaccharides It is best obtained by acid hydrolysis of lactose (milk sugar) a disaccharide of d glucose and d galactose L (—) Galactose also occurs naturally and can be prepared by hydrolysis of flaxseed gum and agar The principal source of d (+) mannose is hydrolysis of the polysaccharide of the ivory nut a large nut like seed obtained from a South American palm... 

Initially, attempts to grow the organism on sodium acetate as the sole source of carbon were unsuccessful, but the difficulties were overcome and mannitol, arabinitol, erythritol, glycerol, maltose, and a,a-trehalose were produced. This was a useful development because conditions were established for the incorporation of [14C] acetate, thereby making labeled polyols and disaccharides available. 

Some disaccharides serve as soluble energy sources for animals and plants, whereas others are important because they are intermediates in the decomposition of polysaccharides. A major energy source for humans is sucrose, which is common table sugar. Sucrose contains a-glucose linked to j6-fructose. About 80 million tons of sucrose are produced each year. Of that, 60% comes from sugar cane and 40% comes from sugar beets. Example treats a disaccharide that is an energy source for insects. 

Sucrose is the most abundant disaccharide isolated from natural sources. All aspects of its chemistry were recently comprehensively reviewed.77 In this paper the new applications of sucrose as synthons in the preparation of fine chemicals will be reported. 

The structural components encountered in E. coli are also present in lipid A of other bacterial sources. Thus, a survey of the structures analyzed shows that lipid A, in general, contain two g/wcoconfigured and pyranosidic D-hexosamine residues (2-amino-2-deoxy-D-glucose, GlcpN, or 2,3-diamino-2,3-dideoxy-D-glucose, GlcpN3N, also termed DAG (49,50)], which are present as a ) -(l — 6)-linked disaccharide (monosaccharide backbones have also been identified, but the respective lipid A lack endotoxic activity). The disaccharide is phosphorylated by one or, in most cases, two phosphate... 

Biologically, carbohydrates are most important as energy sources. This is especially true for monosaccharides, disaccharides, and starches. Starches also function as energy storage molecules in plants. Cellulose is an essential component of plant cell walls. 

An important source of galactose in the diet is the disaccharide lactose present in milk. Lactose is hydrolyzed to galactose and glucose by lactase associated with the brush border membrane of the small intestine. Along with other monosaccharides, galactose reaches the liver through the portal blood. 

The basic units of carbohydrates are the monosaccharides or simple sugars. These may be assembled into more complex structures such as disaccharides, polysaccharides, glycoproteins, and glycolipids. Carbohydrates serve as energy sources, energy reservoirs, structural components, and for cellular communication. 

Lactase The disaccharide lactose is the only carbohydrate present in milk, which is essential for survival of an infant. Consequently, the enzyme lactase is essential for babies. Caucasians retain lactase activity into adulthood, whereas many Asian or African groups progressively lose its activity in adult life. This could, therefore, be described as an adult deficiency disease. Ingestion of milk in these individuals causes nausea, diarrhoea and stomach cramps. Symptoms disappear if milk is excluded from the diet or if a source of lactase is ingested along with or before ingestion of milk. The bacteria that are involved in the production of yoghurt contain the enzyme lactase. 

Carbohydrates serve as a general and easily available energy source. In the diet, they are present as monosaccharides in honey and fruit, or as disaccharides in milk and in all foods sweetened with sugar (sucrose). Meta-bolically usable polysaccharides are found in vegetable products (starch) and animal products (glycogen). Carbohydrates represent a substantial proportion of the body s energy supply, but they are not essential. 

Carbohydrates are diverse with respect to occurrence and size. Familiar mono and disaccharides include glucose, fructose, sucrose (table sugar), cellobiose, and mannose. Familiar polysaccharides are listed in Table 9.1 along with their source, purity, and molecular weight range. 

A disaccharide derivative (42) of more conventional structure has also been isolated from hen oviduct.177 Its structure was confirmed by its conversion into L-fucose and uridine 5 -(2-acetamido-2-deoxy-a-D-glucopyranosyl pyrophosphate) after treatment with a-L-fucosi-dase. Mild, acidic hydrolysis of the ester 42 produces a disaccharide whose structure was confirmed by periodate oxidation. Human milk and colostrum,178 or milk and colostrum of pig,128 are also sources of... 

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