Disaccharides lactose

Disaccharides, e.g., lactose, which yield galactose upon hydrolysis, will also give the sparingly-soluble mucic acid but in poorer 3deld. This reaction may be employed for the differentiation between certain disaccharides lactose — mucic + saccharic acids sucrose — saccharic acid only maltose — saccharic acid only. 

Galactose, a constituent of the disaccharide lactose found in dairy products, is metabolized by a patiiwav that includes the isomerization of UDP-galactose to UDP-glucose. where UDP = uridylyl diphosphate. The enzyme responsible for the transformation uses NAD+ as cofactor. Propose a mechanism. 

The coupling of the protected disaccharides lactose and cellobiose with the pyrazinone scaffold via the 1,3-dipolar cycloaddition reaction was further investigated (Scheme 34). To run the reaction to completion, the use of 2 equiv... 

Similarly, per-O-trimethylsilylated mono- and P-linked disaccharides (lactose and cellobiose, not melibiose) could be converted into the corresponding a-glycosyl iodides, which upon SN2 displacement with CbT using TBACN mainly afforded P-cyano derivatives in good overall yields [191]. The cyanoglycosides were transformed into aminomethyl glycosides via reduction under mild conditions (Scheme 2.52). 

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. 

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. 

The milk of mammals contains the disaccharide lactose as the predominant carbohydrate, to the extent of about 4-8%. Lactose, therefore, provides the basic carbohydrate nutrition for infants, who metabolize it via the hydrolytic enzyme lactase. Lactase enzyme... 

The properties of disaccharides aren t a simple combination of the properties of the two monosaccharides present. For example, the disaccharide lactose (milk sugar) is a reducing sugar containing a (3-D-glucose linked to a D-galactose molecule. 

The main gene, lacX, encodes (J-galactosidase, which hydrolyzes the disaccharide lactose to glucose + galactose to begin their metabolism. 

Brand Name(s) Cholac, Constilac, Constulose, Enulose, Generlac, Kristalose Chemical Class-. Disaccharide lactose analog... 

D-Galactose, a product of hydrolysis of the disaccharide lactose (milk sugar), passes in the blood from the intestine to the liver, where it is first phosphorylated at C-l, at the expense of ATP, by the enzyme galactokinase ... 

Milk and milk products contain the disaccharide lactose, which is digested to galactose and glucose. 

As a result of these activities the ingested carbohydrates, protein and fats are broken down to small molecules suitable for absorption (monosaccharides, amino acids (AAs) and monoglycerides, respectively). In contrast to the situation in the pig, the disaccharide lactose (milk sugar) is only partly utilized by chickens because they lack the enzyme (lactase) necessary for its breakdown. As a result, most milk products are not ideally suited for use in poultry diets. 

The appearance of a 2-D TOCSY experiment resembles in all aspects a COSY. The FI and F2 axes are for proton the diagonal contains 1-D information and even the cross peaks have the same appearance. The difference here is that the cross peaks in a COSY are due to coupled spins while the cross peaks in the TOCSY spectrum arise from relayed coherence transfer. For long mixing times in a TOCSY spectrum, all spins within a spin system appear to be coupled. To appreciate the advantages of TOCSY, we continue with the disaccharide lactose, which has three distinct (i.e., separate) spin systems. 

The disaccharide lactose, is only found in milk and is hydrolysed with water in the presence of an enzyme lactase to form the monosaccharide glucose and galactose. This occurs in the small intestine. Some people, and particularly those from Eastern and African countries, are deficient in lactase so they are intolerant of milk. This can cause diarrhoea. Many African and Chinese foods do not include milk for this reason. 

As noted in the chapter opener, lactose is the principal disaccharide found in milk from both humans and cows. Unlike many mono- and disaccharides, lactose is not appreciably sweet. Lactose consists of one galactose and one glucose unit, joined by a P-1,4 -glycoside bond from the anomeric carbon of galactose to the 4 carbon of glucose. 

In common with other reducing disaccharides, lactose undergoes the usual reactions of aldoses, although precautions must be taken to prevent hydrolysis of the glycosidic bond. Furanoid structures cannot be formed, however, because of the presence of the (1 —> 4)-linkage. 

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