Lactase activity

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. 

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

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. 

Lactose intolerance can be readily managed by ensuring that the amount of lactose ingested is restricted to the amount the individual can tolerate, which is related to the individual s level of residual intestinal lactase activity. Lactose maldigesters can determine their individual threshold for the occurrence of lactose intoler-... 

Application and Principle This procedure is used to determine the neutral lactase activity of enzyme preparations derived from Kluyveromyces marxianus var. lactis and Saccharomyces sp. The assay is based on a 10-min hydrolysis of an o-nitrophenyl-fl-D-galactopyranosidc (ONPG) substrate at 30.0° 0.1° and at pH 6.50. 

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

The specific activity of the enzyme was determined in 0.15M lactose solution (0.02M phosphate buffer, pH 7-0). The activity of the enzyme was expressed in terms of units of activity per mg of enzyme. A unit of activity was defined as a p mole of glucose produced per minute. The soluble lactase activity following affinity chromatography purification was 37-1 units/mg. This represented a 4 fold increase in catalytic potency over the specific activity of the crude enzyme preparation (8.9 units/mg). 

Lactase, which catalyzes the hydrolysis of lactose, is also a bifunctional enzyme. Lactase resides on the same polypeptide chain as phlorizin hydrolase. The entire protein is called lactase-phlorizin hydrolase. The N-lermu ial end of the polypeptide resides in the lumen, and bears the lactase activity. The central portion of the... 

The enzyme lactase catalyzes the hydrolysis of lactose in the lumen of the gut. Generally, intestinal lactase activity occurs at a maximal level from birth through early childhood. Then activity declines to a residual level of 5 10% by the age of. 3 or later in most populations of the world. In persons of European descent, lactase activity can remain at a high level throughout adulthood. Low levels of lactase... 

In samples 1, 4, 6, and 10, the expected activity is 5000 NLU/g, whereas in the rest of the samples the expected activity is 2000 NLU/g. The data presented are averages of two replicates samples. The underlined data were later identified as outliers and were not used in further calculations. Intralaboratory (RSDr) and interlaboratory (RSDr) precision values are also shown. [Reprinted, with permission, from A. J. Engelen and P.H.G Randsdorp, Journal of AOAC International 82 No. 1, 1999, 112—118. Determination of Neutral Lactase Activity in Industrial Enzyme Preparations by a Colorimetric Enzymatic Method Collaborative Study . 1999 by Association of Official Analytical Chemists.]... 

Flatz G. The genetic polymorphism of intestinal lactase activity in adult humans. In Scriver CR,... 

In full-term human infants, lactase activity attains peak values at birth and remains high throughout infancy. As milk intake decreases, lactase levels drop and lactose intolerance may develop. The extent of the decrease of lactase activity distinguishes lactose-tolerant from intolerant populations. 

A common malabsorption syndrome, lactose intolerance, is characterized by nausea, diarrhea, and flatulence after ingesting dairy products or other foods containing lactose. One of the causes of lactose intolerance is a low level of lactase, which decreases after infancy in most of the world s population (nonpersistant lactase or adult hypolactasia). However, lactase activity remains high in some populations (persistent lactase), including Northwestern Europeans and their descendants. 

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.

Intestinal diseases that injure the absorptive cells of the intestinal villi diminish lactase activity along the intestine, producing a condition known as secondary lactase deficiency. Kwashiorkor (protein malnutrition), colitis, gastroenteritis, tropical and... 

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