Disaccharide digestion and maldigestion.

All food carbohydrates are hydrolysed to monosaccharides before transport across the microvillus membrane. The digestion of disaccharides and some oligosaccharides is undertaken by a number of small intestinal brush border enzymes: sucrase-isomaltase, lactase phlorizinhydrolase, maltase-glycoamylase and trehalase. The distribution of the enzymes in the small intestine has been investigated. Different disaccharide maldigestion syndromes have been described. Lactase deficiency in adults is a condition found in the majority of inhabitants of the world. However, the prevalence varies widely between different populations. Sucrase-isomaltase deficiency is a very rare congenital condition except in Greenland. Trehalose maldigestion is likewise rare outside Greenland. Different hypotheses regarding the molecular background of the maldigestion syndromes are discussed.

Má-digestäo e má-absorçäo de carboidratos na infância / Poor carbohidrate digestion and malabsorption in childhood

É apresentada uma extensa revisao abordando aspectos gerais, da fisiopatologia, do diagnóstico e do tratamento dos problemas clínicos decorrentes de alteraçoes na digestao e absorçao dos carboidratos.

Disaccharidases activity in the intestinal mucosa after methotrexate therapy.

Disaccharidases activity in the intestinal mucosa samples of rats was examined after intragastric and intramuscular methotrexate therapy. Methotrexate was given on a twice a week schedule (1 mg/kg body weight). The animals were sacrificed after 2 weeks, 1 month, and 2 months of this therapy. A statistically significant but transient decrease of the lactase and maltase activity was found. The authors suggest studying the beneficial effect of low disaccharidase diet in the first period of methotrexate therapy in children treated with methotrexate.

Physiological constraint on feeding behavior: intestinal membrane disaccharidases of the starling.

Animals clearly choose what they eat and can even choose among chemically different sugars. The physiological and biochemical mechanisms that constrain feeding choices are largely unknown. In this study, European starlings (Sturnus vulgaris) preferred mixture solutions of D-glucose plus D-fructose to equimolar (double molar caloric value) solutions of sucrose. Intubation feeding of sucrose did not increase blood glucose levels. Sucrose is a useless energy source for these birds because they lack a single digestive enzyme (sucrase) on the small intestinal brush border membrane. However, the membranes possessed separate maltase and isomaltase disaccharidases. This expression pattern and expression patterns of membrane disaccharidases among mammals suggest a role for intestinal enzymes in the coevolutionary interactions between vertebrates and their plant food sources.

Hydrolysis of alpha-D-glucopyranosyl-1,6-sorbitol and alpha-D-glucopyranosyl-1,6-mannitol by rat intestinal disaccharidases.

The hydrolyzing activities in rat small intestine for newly developed sugar substitutes, alpha-D-glucopyranosyl-1,6-sorbitol (GPS) and alpha-D-glucopyranosyl-1,6-mannitol (GPM), both of which are produced by hydrogenation of palatinose, were characterized. GPS and GPM were hydrolyzed in mucosal homogenate as well as in brush border membranes of rat small intestine at a slower rate than the rate of hydrolysis of palatinose (30%) and sucrose (6-7%). Gel filtration column chromatography of disaccharidases solubilized from brush border membranes revealed that GPS and GPM were hydrolyzed mainly by sucrase-isomaltase complex and its degradation product, i.e. isomaltase monomer. The isomaltase monomer, purified from small intestine of rats, possessed similar Km values for GPS (2.47 mM) and GPM (5.38 mM) as compared to those of purified sucrase-isomaltase complex. The Vmax values of isomaltase monomer for GPS and GPM were twice as high as those of sucrase-isomaltase, suggesting that GPS and GPM are hydrolyzed by the active site of isomaltase. On the other hand, a small amount (up to 17%) of GPS- and GPM-hydrolyzing activities was ascribed to glucoamylase, which possessed relatively high Km values for GPS (18.7 mM) and GPM (32.9 mM). To examine a physiological significance of GPS- and GPM-hydrolyzing activities, the transmural potential difference (delta PD) evoked by Na+-dependent active transport of glucose, produced by the hydrolysis of these disaccharide alcohols, was measured in everted segments of rat jejunum. The relative rates of absorption of glucose produced by the hydrolysis of GPS and GPM were 36% and 27% of that of palatinose, directly reflecting the hydrolyzing activities determined in jejunal homogenate. These results suggest that the process of hydrolysis is the rate limiting step in digestion-absorption process of palatinose, GPS and GPM in small intestine.