Activation, lactase

Lactase-specific activity/lactase phlorizin hydrolase... 

Calculate the activity (lactase activity per gram) of the enzyme preparation taken for analysis as follows ... 

P-Glycosidase A bifunctional, membrane-bound enzyme located on the brush-border membrane of the small intestine. This single polypeptide enzyme has two activities, lactase and glycosylceramidase, located in different domains of the protein. It will hydrolyze lactose to glucose and galactose. 

Fig. 27.9. Lactase activity. Lactase is a (J-galactosidase. It cleaves the (3-galactoside lactose, the major sugar in milk, forming galactose and glucose.

Lactose intolerance Several studies have shown that lactose-intolerant individuals suffer fewer symptoms if milk in the diet is replaced with fermented dairy products. The mechanisms of action of lactic acid bacteria and fermented dairy products include the following lower lactose concentration in the fermented product due to lactose hydrolysis during fermentation high lactase activity of bacterial preparations used in production and increased active lactase enzyme entering the small intestine with the fermented product or within the viable bacteria. 

Huge amounts of digestive enzymes can be produced by the gastrointestinal tract in order to digest vast quantities of food that may be ingested. Nonetheless, low activities of three enzymes can occur sucrase, lactase or pancreatic amylase, which can lead to problems. 

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. 

In contrast to sulfonylureas and thiazolidinediones, miglitol does not enhance insulin secretion. Miglitol has minor inhibitory activity against lactase and, at recommended doses, would not be expected to induce lactose intolerance. 

Neomycin - Orally administered neomycin increases fecal bile acid excretion and reduces intestinal lactase activity. 

Additionally same study population 10 CD subjects in remission who supplemented GFD with 50 g oats/day for 3 months normal histology Lactase was not expressed in samples from 9 subjects with active CD Lactase was expressed in samples from 10 CD subjects in remission who were challenged subjects... 

Srinivasan, U., Jones, E., Weir, D. G., and Feighery, C. (1999). Lactase enzyme, detected immunohistochemically, is lost in active celiac disease, but unaffected by oats challenge. Am. J. Gastroenterol. 94, 2936-2941. 

Insulin secretion stimulation. Oil, administered orally to young suckling rabbits, quickened and strengthened the rise of immunoreactive serum insulin ". Intestinal brush border membrane. Oil, administered orally to rats at a dose of 10% for 5 weeks, produced an increase in level of saturated fatty acids in the brush border membrane from coconut oil-fed animals. Membrane fluidity was as follows coconut oil less than commercial pellet diet less than corn oil less than fish oil. The membrane hexose content was high in the coconut-fed rats. Hexamines were elevated in coconut-treated rat brush borders. The activities of alkaline phosphatase, sucrase, and lactase were increased "". 

Many i rsons from non-Eastern European-derived cultures are unable to tolerate large quantities of the milk sugar lactose because of the absence of enough of the active digestive enzyme, lactase. In these persons, consumption of lactose results in effects similar to those described for oligosaccharide consumption. Severe intolerance can result in malabsorption of all nutrients from the diet due to diarrhea. 

Lactose hydrolysis with immobilized systems is the method of choice when regular production of hydrolyzed syrups on a large scale is required. The best-known of these is the Corning immobilized system, which uses lactase from Aspergillus niger covalently bound to a controlled-pore silica carrier. The particle size is 0.4 to 0.8 mm, the wet bulk density is 0.6, the activity is near 500 U/g at 50°C, and the optimal pH of operation is between 3.2 and 4.3. Estimated laboratory life is 2 years (Dohan et al. 1980). There are at least two of these plants in commercial operation, one in the Untied States and one in the United Kingdom, each a joint venture with Corning. 

In a more recent study (Asp et al. 1980), six oligosaccharides from hydrolyzed lactose milk which had been treated with K. lactis lactase were isolated from their structure, it was concluded that the enzyme had high transglycosylation activity with specificity for the formation of /3-(l,6)-galactosidic bonds. 

The nutritional and physiological effects of lactose in the diet have become of major interest to health professionals and the public with the finding that about 70% of the world population has low levels of lactase activity in the intestine and, in many cases, an intolerance to lactose. A voluminous literature has developed (Delmont 1983 Renner 1983 Paige and Bayless 1981). Most problems with lactose digestion are attributable to the lactose molecule, but others may arise from the galactose moiety liberated on hydrolysis. 

There are several forms of intolerance to lactose and galactose. Primary adult lactase deficiency is a normal age-related decrease in lactase activity seen in the majority of adults. Secondary lactase deficiency is a transient state of low enzyme activity following injury to the intestinal mucosa as a result of diseases such as celiac sprue, infectious gastroenteritis, and protein-calorie malnutrition. The last two states are common conditions (Dahlqvist 1983). 

A review of medical research has led to the conclusion that ethnic differences concerning lactose intolerance are largely genetic in origin. A culture historical hypothesis has been offered to explain the present-day occurrence of various Old World groups with high and low incidences of lactose intolerance based on milk use (Simoons 1981). It is currently believed that the decline in lactase activity with age is determined by an autosomal recessive gene and is not influenced by the amount of lactose consumed. 

Low lactase activity has been suggested as a factor leading to osteoporosis as a result of either reduced calcium intake or reduced calcium absorption. However, results are conflicting and further studies will be necessary to resolve this question (Paige and Bayless 1981). The relationship between irritable bowel syndrome and lactase deficiency is still unclear, but hypolactasia does not appear to be a major problem in patients with this condition (Paige and Bayless 1981). 

Kilara, A. and Shanani, K. M. 1976. Lactase activity of cultured and acidified dairy products. J. Dairy Sci. 59, 2031-2035. 

National Dairy Council. 1985. Nutritional implications of lactose and lactase activity. Dairy Council Digest 56, 25-30. 

Protein Advisory Group of the United Nations. 1972. PAG statement 17 on low lactase activity and milk intake. PAG Bull 2(2), 9-11. 

Table-TV shows the effect ot fhe LMW fraction on the activity of some of these enzymes in vitro. Maltase, lactase and invertase were competitively inhibited at a concentration of 10 mg/ ml. When the effectsof a range of concentrations (2.5-20 mg/ml) of the LMW fraction were studied, it was revealed that the inhibition was not of the pure competitive type. Table V shows the effect of the HMW fraction. Low concentrations had to be used in the assays, as the intense brown color of this fraction interfered with the spectrophotometric measurements. In spite of this a strong competitive inhibition of lactase and of invertase was found. Maltase was also inhibited, and, to a lesser extent, even trehalase. a-Amylase from saliva was not affected at the concentration tested.

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