Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.108 (lactase)
 2,133 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Intestinal brush border enzymes have heterogeneous rates of turnover, the largest proteins having the fastest turnover. Since the membrane faces the intestinal lumen, the effects of pancreatic factors were examined in mediating this turnover. Surgical subtotal pancreatectomy was used as an experimental model to study the turnover of brush border proteins in the absence of most pancreatic secretions. 2. Subtotal (95%) pancreatectomy of rats was found to cause elevations by about 50% of total activity and specific activities of certain brush border enzymes (maltase, sucrase, lactase), but not of others (alkaline phosphatase, trehalase). Rats were judged to be functionally deficient in pancreatic proteolytic enzymes (a) by demonstration of vitamin B-12 malabsorption, which was corrected by trypsin, and (b) by the finding of only about 20% of proteolytic activity appearing in the lumen after a test meal when compared to control. 3. To measure protein turnover in vivo the method of double labelling was used, where [3H]- and [14C]valine were administered intraduodenally in sequence 10 h apart. With this technique, a high 3H/14C ratio is correlated with rapid turnover. Proteins with apparent molecular weights of about 200 000-270 000 were found to turn over more rapidly than smaller proteins. 3H/14C ranged from 4.7 to 6.2 in animals without pancreatic insufficiency. In the face of decreased pancreatic proteolysis, the 3H/14C ratio was 2.3-3.1, similar to that of proteins with a slow half life. 4. Estimates of relative synthetic rates of large brush border proteins were lower than normal in pancreatectomized animals, but were constant over the period of the labelling experiment. The high enzyme levels in the face of lower synthetic rates confirms that, at the new steady rate, degradation rates must be slower for large brush border proteins in pancreatic insufficiency. 5. In vitro, using purified brush borders, unfractionated pancreatic enzymes were found to remove sucrase, maltase and lactase, but not alkaline phosphatase and trehalase. The enzyme most potent in this respect was the pancreatic protease, elastase. Non-proteolytic enzymes (amylase, lipase, phospholipase A) were inactive in removing enzyme from the brush border. The addition of elastase to pancreatectomized animals in vivo restored the rapid turnover rate of large brush border proteins. 6. A model is thus proposed for the normal catabolism of some large intestinal brush border proteins. It is suggested that the surface of intestinal absorptive cells is being constantly remodelled, and that certain surface enzymes are in part removed from the membrane by the action of pancreatic proteases. A possible special role for elastase is suggested.
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PMID:The possible role of pancreatic proteases in the turnover of intestinal brush border proteins. 114 88

Dietary fibres (Plantago ovata seeds, P. ovata husks, wheat bran, alfalfa, pectin, xylan) were incubated in vitro with gastrointestinal enzymes (pepsin, trypsin, chymotrypsin, lipase, alpha-amylase, maltase, lactase) in buffer solutions at concentrations of 1-5% for 10-30 min at 37 degrees C. All fibres induced sometimes pronounced changes in enzyme activity, but the effect of the different fibres on the various enzymes varied individually and was not predictable. Both P. ovata preparations had no (pepsin, trypsin, alpha-amylase) or only stimulating (chymotrypsin, lipase, lactase) actions whereas all other fibres showed inhibiting as well as stimulating influences. Wheat bran induced the most pronounced alterations increasing lipase, maltase and lactase activity and inhibiting alpha-amylase activity. Pectin and xylan were comparable in decreasing lipase and pepsin activity and in increasing chymotrypsin activity but had opposite effects on maltase activity. Alfalfa was able to stimulate lactase and lipase activity but depressed trypsin and alpha-amylase activity. The inactivation of enzymes by dietary fibres can, at least partly, be explained by adsorption to the fibre or by the presence of enzyme inhibitors especially in natural compounds. The reasons for activation processes are unknown. As enzyme activities are decisive for food digestion, the properties of the individual fibres should be carefully considered when used as dietary supplement in physiological or pathological conditions.
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PMID:Interference of dietary fibres with gastrointestinal enzymes in vitro. 248 92

The development of the human fetal gastrointestinal tract takes place early during gestation. The pancreas although developed by morphological means at the 16th week of gestation excretes its exocrine enzymes later at the 24th week of gestation except for amylase which reaches its full activity 6 months after birth. Trypsinogen secreted at the 24th week is activated into trypsin by enterokinase at the 26th week of gestation whereas lipase and colipase are secreted from the 24th week. The small intestine starts developing at the 10th week morphologically and functionally. At the same time when villi and crypts start to develop at the 11th to 12th week the first enzyme activities can be detected, i.e. sucrase-isomaltase, maltase-glucoamylase and lactase. Also peptidases and lysosomal hydrolases are measured at this age. With the exception of lactase, intestinal enzymes reach sufficient activities at the 25th week of gestation. Lactase activity remains low until the 32nd-34th week. For the digestion and absorption of lipids, protein and carbohydrates the gastrointestinal tract of premature infants under 1500 g in rather well equipped. Lipids are hydrolysed by the mutual action of breast milk lipase, lingual lipase, gastric lipase and pancreatic lipase. The carbohydrates lactose and oligosaccharides as supplements to breast milk are hydrolysed by lactase, sucrase-isomaltase and maltase-glucoamylase. Breast milk proteins and cows milk hydrolysates are digested by pancreatic proteases into oligopeptides which can be hydrolysed within the lumen by brush border peptidases and be absorbed. Peptides also can actively be transported through the microvillus membrane and be hydrolyzed by intracellular peptidases.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:[Nutrition of premature infants below 1,500 g: enteral prerequisites]. 309 34

Intestinal and pancreatic enzyme activities are known to respond to changes in dietary composition. Studies in rats and humans suggest that adaptive mechanisms differ between species in response to altered intakes of carbohydrate and fat. Because of increased use of the pig in the study of human nutrition, we compared the responses of pancreatic enzymes and intestinal disaccharidases in groups of 7- to 10-week-old pigs fed either high-carbohydrate/low-fat (70 cal% starch, 25% protein, 5% fat) or low-carbohydrate/high-fat (5, 25, 70%, respectively) diets for 7 and 30 days. No changes were observed in the activities for lactase, trypsin, or chymotrypsin or in the tissue protein concentrations, regardless of diet duration. High-carbohydrate/low-fat intake resulted in higher specific activities of sucrase, maltase, and amylase for both periods studied. Low-carbohydrate/high-fat intake resulted in higher specific activities of pancreatic lipase for both periods studied. The response of the intestinal disaccharidases differs from that observed previously in rodents but resembles the response reported in humans. Conversely, amylase and lipase responded similarly to the pattern in the rat. These data support the continued use of the pig as a suitable model in the study of adaptation to altered intakes of carbohydrate and fat.
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PMID:Effect of diet on intestinal and pancreatic enzyme activities in the pig. 319 78

Protein, fat and carbohydrate absorption in preterm infants fed on human milk or formulae are reviewed. Even in the most premature infants absorption of protein is satisfactory. Nitrogen net absorption is about 85-90% of intake and results slightly lower with human milk than with formulae. The lower apparent digestibility of human milk is probably due to the poorly degraded IgA immunoglobulins and the rapid transit time. Lactose is well tolerated by the preterm infants despite the low lactase activity at birth. Glucose polymers, which have a low osmotic activity and are suitable for increasing carbohydrate intake of formulae, are well absorbed probably for the activity of salivary amylase and brush border glucoamylase, which have been shown to be well developed at birth. Premature infants absorb fat poorly. This malabsorption that increases with the lowering of gestational age is due to low pancreatic lipase activity and to low intraluminal concentration of bile salts. Due to its bile stimulated lipase activity, non-heat-treated human milk used at least in part is an effective method to improve fat absorption in preterm infants. Faecal energy determined using a calorimetric bomb appears to be a simple and an accurate method to predict faecal fat and avoiding expensive and cumbersome analysis.
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PMID:[Absorption of proteins, carbohydrates and fats in the preterm neonate]. 357 19

The effect of a chronic exposure to sublethal concentration of mercuric chloride (0.3 mg/l) on the activities of some enzymes in the digestive system of the teleost fish Channa punctatus was examined after 15 and 30 days of treatment. Glucose-6-phosphatase was significantly inhibited in the intestine and pyloric caeca. No marked alterations were observed in the activities of maltase and lactase except for elevation in maltase activity and inhibition in lactase activity in the intestine and pyloric caeca after 15 days of treatment. Three peptidases (aminotripeptidase, glycylglycine dipeptidase and glycyl-1-leucine dipeptidase) showed decreased activities in all parts of the digestive system. A decrease was also observed in the activity of lipase except for the stomach where inhibition after 15 days was insignificant. The results indicate that the activities of all the enzymes examined are inhibited in intestine and pyloric caeca and digestion of proteins and lipids may be more affected by mercury than the digestion of some carbohydrates.
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PMID:Changes in the activities of some digestive enzymes of Channa punctatus, exposed chronically to mercuric chloride. 624 41

Mercury is known to modify enzyme activity through oxidation of thiol groups and respective reverse reactions in vitro and in vivo. However, variations in the activity of carbohydrates, and the significance of this variation after mercury poisoning in different species, has not been established. In the present report, the effects of inorganic mercury on selected hepatic enzymes was studied in the freshwater fish Channa punctatus. Quantitative data clearly showed a dose-response relationship between the amount of mercury retained in the liver and inhibition of enzymes (i.e. alkaline phosphatase, glucose-6-phosphatase, amylase, maltase, lactase, lipase and dehydrogenases). Mechanisms and significance of their modification have also been discussed.
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PMID:Co-enzyme effects of inorganic mercury in the liver of a freshwater fish Channa punctatus. 718 6

Activities of twelve hydrolytic enzymes in the digestive tract of young rabbits before weaning (4 weeks old) and adult rabbits (3 months old) were measured. The principal digestive enzymes in both groups of rabbits appeared to be amylase (EC 3.2.1.1), maltase (EC 3.2.1.20), pectinase (EC 3.2.1.15) and proteinases. The stomach of young rabbits contained most of the lipolytic activity and 45.7% of the total proteolytic activity of the digestive tract. The highest specific activities (per g digesta) of amylase, maltase and proteinase in young rabbits were found in the small intestine. Total activities (per segment) of amylase and maltase in the small intestine and the caecum were similar. Activities of cellulase (EC 3.2.1.4), inulinase (EC 3.2.1.7) and beta-glucosidase (EC 3.2.1.21) were low and activity of pectinase was fairly high in all segments of the digestive tract. The highest activity of urease (EC 3.5.1.5) was found in the caecum. Enzymic profiles of the colonic chymus resembled those of the caecum. Total hydrolytic activity was lower in the colon than in the caecum. Specific activities of amylase and invertase (EC 3.2.1.26) were lower and those of inulinase and lactase (EC 3.2.1.23) higher in 4-week-old rabbits than in 3-month-old rabbits. Gastric proteinase represented almost half of the total proteolytic activity of the digestive tract, whereas lipolytic activity of gastric contents was not found in measurable quantities in adult rabbits. The caecal contents of adult rabbits contained most of the total activity of lipase (EC 3.1.1.3), cellulase, xylanase (EC 3.2.1.32), pectinase, lactase, invertase, beta-glucosidase and urease present in the digestive tract.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Distribution of activity of hydrolytic enzymes in the digestive tract of rabbits. 753 89

The growth of group A human, bovine, equine and porcine rotaviruses were enhanced by pretreatment of virus with pancreatin, trypsin, protease, alkaline phosphatase or pepsin and incorporation of these enzymes in maintenance medium. In contrast, alpha-amylase or lipase inhibited the growth of equine and porcine rotaviruses. The other enzymes, adenosine deaminase, lactase, lysozyme, ribonuclease or triose-phosphate isomerase gave little or no change in the growth of all four rotaviruses.
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PMID:Effect of enzymes on the growth of human and animal rotaviruses. 754 24

Epidermal growth factor and related substances mediate their effects on epithelial cells through binding to high-affinity receptors (EGF-R) at their basolateral surface and it is hypothesized that this growth factor system play a major role in gut morphogenesis and maintenance. The current review emphasizes on analyzing the expression and the biochemical characteristics of EGF-R in human fetal gut segments and correlating the biological actions of EGF-R ligands. They appear to be primarily involved in the local regulation of epithelial cell proliferation in which EGF-R are abundant. Alternatively, EGF-R ligands exert some precocious maturative effects by increasing intestinal lactase activity and decreasing brush border hydrolases in colon while they down modulate the expression of segment-specific markers of terminal differentiation such as sucrase, trehalase and glucoamylase in the intestine and chief cell lipase in the stomach. Such effects are consistent with the identification of receptors at the surface of all epithelial cell types, illustrating the modulatory role of EGF on differentiated gut epithelial cells. Comparison with animal models illustrates similar biochemical properties of receptors and underlines physiological aspects specific to human gut development. The relevance for ligand heterogeneity is also discussed and tentatively associated with different delivery pathways or physiological responses.
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PMID:Ontogeny of EGF receptors in the human gut. 988 80


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