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PubMed1991

Lactose metabolism in Lactobacillus bulgaricus: analysis of the primary structure and expression of the genes involved.

The genes coding for the lactose permease and beta-galactosidase, two proteins involved in the metabolism of lactose by Lactobacillus bulgaricus, have been cloned, expressed, and found functional in Escherichia coli. The nucleotide sequences of these genes and their flanking regions have been determined, showing the presence of two contiguous open reading frames (ORFs). One of these ORFs codes for the lactose permease gene, and the other codes for the beta-galactosidase gene. The lactose permease gene is located in front of the beta-galactosidase gene, with 3 bp in the intergenic region. The two genes are probably transcribed as one operon. Primer extension studies have mapped a promoter upstream from the lactose permease gene but not the beta-galactosidase gene. This promoter is similar to those found in E. coli with general characteristics of GC-rich organisms. In addition, the sequences around the promoter contain a significantly higher number of AT base pairs (80%) than does the overall L. bulgaricus genome, which is rich in GC (GC content of 54%). The amino acid sequences obtained from translation of the ORFs are found to be highly homologous (similarity of 75%) to those from Streptococcus thermophilus. The first 460 amino acids of the lactose permease shows homology to the melibiose transport protein of E. coli. Little homology was found between the lactose permease of L. bulgaricus and E. coli, but the residues which are involved in the binding and the transport of lactose are conserved. The carboxy terminus is similar to that of the enzyme III of several phosphoenolpyruvate-dependent phosphotransferase systems.

Base Sequence↗
PubMed1998

Regulation of lactose utilization genes in Staphylococcus xylosus.

The lactose utilization genes of Staphylococcus xylosus have been isolated and characterized. The system is comprised of two structural genes, lacP and lacH, encoding the lactose permease and the beta-galactosidase proteins, respectively, and a regulatory gene, lacR, coding for an activator of the AraC/XylS family. The lactose utilization genes are divergently arranged, the lacPH genes being opposite to lacR. The lacPH genes are cotranscribed from one promoter in front of lacP, whereas lacR is transcribed from two promoters of different strengths. Lactose transport as well as beta-galactosidase activity are inducible by the addition of lactose to the growth medium. Primer extension experiments demonstrated that regulation is achieved at the level of lacPH transcription initiation. Inducibility and efficient lacPH transcription are dependent on a functional lacR gene. Inactivation of lacR resulted in low and constitutive lacPH expression. Expression of lacR itself is practically constitutive, since transcription initiated at the major lacR promoter does not respond to the availability of lactose. Only the minor lacR promoter is lactose inducible. Apart from lactose-specific, LacR-dependent control, the lacPH promoter is also subject to carbon catabolite repression mediated by the catabolite control protein CcpA. When glucose is present in the growth medium, lacPH transcription initiation is reduced. Upon ccpA inactivation, repression at the lacPH promoter is relieved. Despite this loss of transcriptional regulation in the ccpA mutant strain, beta-galactosidase activity is still reduced by glucose, suggesting another level of control.

Amino Acid Sequence↗
PubMed1986

Lactose digestion by human jejunal biopsies: the relationship between hydrolysis and absorption.

The relationship between lactose hydrolysis and absorption of released glucose was investigated by determining the kinetics of lactose digestion by jejunal biopsies incubated in vitro. Lactase activity in intact biopsies correlated with conventional assay of tissue homogenates (r = 0.85, p less than 0.001), and glucose uptake from 28 mM lactose was directly proportional to lactase activity (r = 0.95, p less than 0.001) in 21 subjects with normal lactase levels, six with hypolactasia (primary or secondary to coeliac disease) and two with lactose intolerance but normal lactase activity. Kinetic analysis at 0.56-56 mM lactose in five normal subjects showed saturable kinetics for hydrolysis (app Km = 33.9 +/- 2.2 mM; app Vmax = 26.5 +/- 1.1 nmol/min/mg dry weight) but glucose uptake could be fitted to a model either of saturable uptake (app Kt = 47.2 +/- 0.3 mM; app Jmax = 14.1 +/- 0.2 nmol/min/mg) or saturable uptake plus a linear component (app Kt = 21.3 +/- 1.15; app Jmax = 4.59 +/- 0.12; app Kd = 0.093 +/- 0.010 nmol/min/mg/mM). The proportion of glucose taken into the tissue did not significantly exceed 50% of the total released at any lactose concentration suggesting the lack of an efficient capture mechanism for the released glucose. The results suggest that lactose hydrolysis is the rate limiting step in the overall absorption of glucose from lactose in vitro, and that the relationship between hydrolysis and absorption is the same in normal subjects and in hypolactasic subjects.

Adolescent↗
PubMed1984

Effects of lactose on calcium absorption and secretion by rat ileum.

The direct effects of lactose on net intestinal calcium absorption were determined by measuring unidirectional steady-state calcium fluxes in vitro under short-circuited conditions in segments of rat ileum. The isosmotic mucosal additions in segments of rat ileum. The isosmotic mucosal addition of lactose (160 mM) increased net calcium absorption (J net) by increasing the absorptive flux from mucosa to serosa (Jm----s) and reducing the secretory flux from serosa to mucosa (Js----m). Lactose also reduced tissue conductance and short-circuit current and reversed tissue polarity. 1,25-Dihydroxyvitamin D3 administration (50 ng/day for 4 days) increased J net from secretion to no net flux (Jm----s = Js----m), and lactose increased J net further to net absorption. Removal of sodium from the medium, like lactose addition, increased J net by increasing Jm----s and reducing Js----m. The replacement of medium sodium with choline abolished a further increase of J net by lactose. These results show that lactose increases net calcium absorption in the absence of transepithelial electrochemical or osmotic gradients. Transcellular calcium transport may be stimulated by lactose by hyperpolarization of the brush border as a result of reduced mucosal sodium.

Absorption↗
PubMed1984

Relation between dietary-induced increase of intestinal lactase activity and lactose digestion and absorption in adult rats.

To study the relation between dietary-induced increase of intestinal lactase activity and lactose absorption, 11-wk-old rats were fed either a high-starch (70 cal%), low-fat (7 cal%) diet or a low-starch (5 cal%), high-fat (73 cal%) diet for 7 days. Food intake and body weight changes were similar in the two dietary groups. In the first experiment, lactose absorption was studied in vivo after oral administration of 600 mg lactose (10% solution in water with added [3H]PEG) to rats fasted for 16 h. Groups of rats were killed at time 0 and at 1-h intervals for the next 3 h. Lactase activity and lactose absorption were significantly higher (P less than 0.01) in the high-starch group than in the low-starch group. In the subsequent experiment, 9-wk-old rats were fed the two isocaloric diets for 3 days. By use of the everted sac technique, we have demonstrated a significantly higher absorption of monosaccharides from lactose in the high-starch diet group; also, glucose transport was higher in the high-starch diet-fed animals. When Tris, an inhibitor of lactase, was added into the mucosal fluid, absorption of lactose was abolished and no effect was seen on glucose absorption (in vivo and in vitro). In both experiments, significant linear regression was established between lactase activity and lactose absorption. Our results thus show that the increase in lactase activity, induced by feeding a high-starch diet to adult rats, is accompanied by an increased capacity to hydrolyze lactose and absorb the constituent monosaccharides.

Absorption↗
PubMed1997

Chronic lactose intake modifies the gastric emptying of monosaccharides but not of disaccharides in weanling rats.

Ninety-six weanling male Wistar rats were fed for four weeks one of two different chows: a normal rat chow containing 55.5% (w/w) starch (control group, N = 48) or a rat chow in which starch was partially replaced by lactose, in such a way that the experimental group (N = 48) received 35.5% (w/w) starch and 20% (w/w) lactose. The gastric emptying of fluid was then studied by measuring the gastric retention of four test meals containing lactose (5% or 10%, w/v) or glucose+galactose (5% or 10%, w/v). Homogenates of the small intestine were assayed for lactase activity. The gastric retention values were obtained 15 min after orogastric infusion of the liquid meals. The median values for gastric retention of the 5% lactose solutions were 37.7% for the control group and 37.0% for the experimental group (P > 0.02). For the 10% lactose solution the median values were 51.2% and 47.9% (P > 0.02) for the control and experimental groups, respectively. However, for the 2.5% glucose +2.5% galactose meal the median gastric retention was lower (P < 0.02) in the group fed a lactose-enriched chow (38.5%) than in the control group (41.6%). For the 5% glucose +5% galactose solution the median values were not statistically different between groups, 65.0% for the control group and 58.8% for the experimental group. The median values of the specific lactase activity in the small intestine homogenate was 0.74 U/g in the control group and 0.91 U/g in the experimental group. These values were not statistically different (P > 0.05). These results suggest that the prolonged ingestion of lactose by young adult rats changes the gastric emptying of a solution containing 5% monosaccharides. This adaptation may reflect the desensitization of intestinal nutrient receptors, possibly by an osmotic effect of lactose present in the chow.

Animals↗
PubMed2002

Efficacy of partially hydrolyzed corn syrup solids as a replacement for lactose in manufactured liquid diets for neonatal pigs.

Feeding manufactured liquid diets to early-weaned pigs improves growth performance and reduces days to market weight compared with pigs receiving pelleted dry feed. Few alternative dietary ingredients are utilized in manufactured liquid diets other than byproducts of the dairy industry, especially for sources of carbohydrates. This experiment was designed to evaluate the efficacy of starch from partially hydrolyzed corn syrup solids (CSS), at two different levels of hydrolyzation, as a replacement for lactose in manufactured liquid diets. Forty-eight pigs were removed from sows at 1 d of age and randomly assigned to one of three treatments: 1) control with lactose as the carbohydrate source, 2) lactose replaced (gram for gram) with CSS (dextrose equivalent [DE]-20), and 3) lactose replaced with DE-42. In addition, 10 pigs were randomly removed from several litters to provide estimates of initial body composition and small intestinal variables. Twenty-four pigs were removed from the study on d 10 of treatment, and the remaining 24 pigs were removed on d 20 of treatment. Pigs averaged 9,845 +/- 191 g at d 20 of treatment regardless of dietary treatment (P > 0.20). No differences in ADG, ADFI, or feed efficiency were detected between treatment groups from d 0 to 20 (P > 0.19). Whole-body water, protein, lipid, and ash accretion rates were unaffected by dietary treatment from d 0 to 10 or from d 0 to 20 (P > 0.20). The replacement of lactose with CSS did not affect intestinal villi height or width, or crypt depth (P > 0.10). Pigs fed lactose tended to have greater lactase activity on d 10 than pigs fed CSS (P < 0.07). Also, pigs fed lactose tended to have lower oligosaccharidase activity than pigs fed the DE-20 diet on d 20 (P < 0.07). No other differences in lactase, maltase, or long oligosaccharidase specific activity on d 10 or 20 of treatment were detected (P > 0.12). Plasma urea nitrogen concentrations were unaffected by diet on d 10 and 20 of treatment. In addition, dry matter digestibility of the diets averaged approximately 85.6 +/- 0.8% and was unaffected by dietary treatment or day of treatment. These results suggest that partially hydrolyzed CSS can be used as a replacement for lactose in manufactured liquid diets for neonatal pigs.

Animal Feed↗
PubMed1994

Comparison of effects of chicken cecal microorganisms maintained in continuous culture and provision of dietary lactose on cecal colonization by Salmonella typhimurium in turkey poults and broiler chicks.

A mixed bacterial culture derived from the cecal contents of an adult broiler chicken was maintained in continuous-flow culture and tested for effectiveness in Salmonella colonization reduction in broiler chicks and turkey poults. Day-old chicks and poults in two separate experiments were divided into four groups and provided a standard corn-soybean diet with: 1) no culture, no lactose (control); 2) 5% dietary lactose; 3) broth culture by crop gavage; 4) culture by crop gavage and 5% lactose. All groups were challenged orally on Day 3 with 10(4) Salmonella typhimurium. At 10 and 21 d of age the chicks provided culture and lactose had significantly (P < .05) fewer Salmonella per gram of cecal contents than controls. Poults provided culture by gavage and lactose also had significantly (P < .05) fewer Salmonella per gram of cecal contents than control poults, but the number was 100- to 1,000-fold higher than that of the chicks provided the same treatment. The percentage of Salmonella cecal-culture-positive chicks provided culture and lactose was significantly reduced at 10 and 21 d of age in both experiments compared with controls, but the percentage of cecal-culture-positive poults was significantly different from controls only at 21 d in one of the two experiments. Chicks provided culture and lactose had significantly fewer Salmonella colony-forming units per gram and significantly fewer cecal-culture-positive birds than poults provided culture and lactose in both experiments. The results indicate that cultures of cecal bacteria that effectively reduce Salmonella colonization in broiler chicks may not be as effective for reduction of Salmonella colonization in turkey poults.

Animals↗
PubMed2004

[Effects of lactose inducing on expression of Helicobacter pylori rUreB and rHpaA, and Escherichia coli rLTKA63 and rLTB].

OBJECTIVE: To determine the effects of lactose inducing on the expression of recombinant Helicobacter pylori rUreB and rhpaA, and Escherichia coli rLTB and rLTKA63. METHODS: BIO-RAD gel image analysis system was applied to detect the outputs of the recombinant proteins. SDS-PAGE was performed to measure the target protein expression of recombinant genes at various periods of growth, different lactose concentrations, various inducing temperatures and times. The results of the target protein expression induced by lactose were compared to those by isopropyl-beta-D-thiogalactoside (IPTG). RESULTS: Lactose showed higher efficiency to induce the expression of rHpaA, rUreB, rLTB and rLTKA63 than IPTG. The expression outputs of target recombinant proteins induced at 37 degrees C were remarkably higher than those at 28 degrees C. The optimal expression parameters were 0.8 of OD600 value, 50 g/L of lactose, 4 hours of inducing time for rHpaA, and 1.2 of OD600 value, 100 g/L of lactose, 5 hours of inducing time for both the rUreB and rLtB,and 0.8 of OD600 value, 100 g/L of lactose, 4 hours for rLTKA63. CONCLUSION: Lactose, a sugar with non-toxicity and low cost, is able to induce the recombinant genes to express the target proteins with higher efficiency than IPTG.

Adhesins, Bacterial↗
PubMed1989

The role of milk and lactose intolerance in Ethiopian patients with non-ulcer dyspepsia: a case control study.

Milk intolerance, lactose intolerance and non-ulcer dyspepsia are common among Ethiopians. This study, therefore, was designed to find out if milk intolerance associated with lactase deficiency account for non-ulcer dyspepsia. Ninety-eight patients with non-ulcer dyspepsia and 95 controls were examined and interviewed for demographic data and milk drinking habits. Then each had a lactose tolerance test (LTT), stool examination for pH, ova and parasites. The demographic characteristics and the number of milk drinkers were comparable in the 2 groups. However, milk intolerance and lactose intolerance were significantly higher among the patients with non-ulcer dyspepsia than among the control group (p less than 0.01, p less than 0.05 respectively). The combination of milk intolerance, lactose intolerance and LTT was also significantly different (p less than 0.01). The mean stool pH was markedly reduced after lactose ingestion and there were more ova and parasites in the stools of the control group. These observations suggest that milk intolerance and/or lactose intolerance account significantly for the symptoms of the patients with non-ulcer dyspepsia. However, since lactose intolerance and abnormal LTT are very common among adult Ethiopians symptoms related to the drinking of milk should be interpreted with caution vis-a-vis the results of the lactose loading test.

Adolescent↗
PubMed1988

[Lactose tolerance and milk consumption: myths and realities].

The disaccharide lactose, the principal carbohydrate of animal milks, requires the enzyme lactase to split it to glucose and galactose. Undigested lactose passes to the colon where fermentation produces hydrogen and short-chain fatty acids that can cause abdominal distention, pain and sometimes diarrhea. Persistence of intestinal lactase after early childhood, is inherited as a highly-penetrant autosomal dominant genetic characteristic. On the basis of a review of over 560 references, all available data on the primary loss of intestinal lactase in Latin American populations are presented in tabular form. Prevalence of lactose non-digesters in Latin American populations ranges from 45% to 100%. However, this is not a reliable predictor of the acceptability of milk and milk products containing lactose. Milk is being used successfully for the supplementary feeding of children worldwide, and most lactose non-digesters can tolerate at least 240 ml of milk or the lactose equivalent in other products. Lactose maldigestion does not interfere with the absorption of the protein and essential micronutrients in milk. Information is provided on the lactose content of milk and milk products, on the usual milk consumption of Latin American populations, and on worldwide experimental and field observations of milk acceptability. Both adaptation to continued use of milk and milk products and relationships of milk use to various disease states in which intestinal lactase activity may be reduced are discussed. Some types of yoghurts are better tolerated because of the lactase activity of the bacteria used in their fermentation. For unusually intolerant individuals commercial enzyme preparations are available for addition to milk products but for most persons the additional cost is unnecessary.

Adult↗
PubMed1982

Sugar transport by the bacterial phosphotransferase system. Regulation of other transport systems (lactose and melibiose).

The role of the phosphoenolpyruvate-dependent phosphotransferase system (PTS) in the phenomenon of inducer exclusion was examined in whole cells of Salmonella typhimurium which carried the genes of the Escherichia coli lactose operon on an episome. In the presence of the PTS substrate methyl alpha-D-glucopyranoside, the extent of accumulation of the lactose analog methyl beta-D-thiogalactopyranoside was reduced. A strain carrying a mutation in the gene for Enzyme I was hypersensitive to the PTS effect, while a crr mutant strain was completely resistant. Influx, efflux, and exchange of galactosides via the lactose "permease" were inhibited by methyl alpha-glucoside. This inhibition occurred in the presence of metabolic energy poisons, and therefore does not involve either the generation of metabolic energy or energy-coupling to the lactose transport system. When the cellular content of the lactose permease was increased by induction with isopropyl beta-D-thiogalactopyranoside, cells gradually became less sensitive to inducer exclusion. The extent of inhibition of methyl beta-thiogalactoside accumulation by methyl alpha-glucoside was shown to be dependent on the relative cellular content of the PTS and lactose system. The data were consistent with an hypothesis involving partial inactivation of galactoside transport due to interaction between a component of the PTS and the lactose permease. By examination of the effects of the PTS and lactose uptake and melibiose permease-mediated uptake of methyl beta-thiogalactoside, it was further shown that the manner in which inducer exclusion is expressed is independent on the routes available to the non-PTS sugar for exit from the cell.

Biological Transport↗
PubMed1983

Lactose enhances mineral absorption in infancy.

To determine if lactose promotes the intestinal absorption of calcium and other minerals by infants, metabolic balance studies were performed with infants fed two formulas nearly identical in composition except for carbohydrate. One contained only lactose and the other contained sucrose and corn starch hydrolysate. Each of six normal infants had two balance studies performed with each formula in alternating sequence. When lactose was the carbohydrate, net absorption and net retention of calcium were significantly greater than when lactose was not present in the formula. Absorptions of magnesium and manganese were also significantly enhanced by lactose. Absorptions of copper and zinc were somewhat greater (not statistically significant) when lactose was present, whereas absorption of iron was not affected. Absorption of phosphorus was not different, but urinary excretion was less when the lactose containing formula was fed and, hence, net retention of phosphorus was significantly enhanced. These results confirm findings from animal studies and previous human studies and show that, in infants, lactose has a significant and sustained promoting effect on absorption of calcium and other minerals.

Calcium↗
PubMed1998

Lactase is unchanged in suckling mice fed with lactose-free milk.

At weaning, mammals switch from milk to complex adult food, and change from a lactose-rich to a lactose-free diet. At the same time, the small intestine matures resulting in changes in lactase expression and the onset of sucrase. The aim of this study was to analyze the effect of premature and specific depletion of lactose on maturation of the small intestine and on lactase expression in suckling mice. For this purpose, from postnatal days 10 to 16, suckling mice were fed by transgenic alpha-lactalbumin-deficient females that produce lactose-free milk. Pups fed with lactose-free milk had a lower body weight than controls fed by wildtype females. They also displayed hypotrophy of intestinal muscle layers, but no obvious alterations in the morphology of the intestinal epithelium. The level of lactase activity as well as the longitudinal distribution of corresponding mRNA were unchanged compared to suckling animals nourished with normal lactose-containing milk. Finally, there was no premature onset of sucrase expression. We conclude that feeding suckling mice for six days with lactose-free milk does not provoke any premature maturation of the small intestine. Thus, decreasing lactose intake is not a major cause for the modifications of lactase expression which occur at weaning.

Animals↗
PubMed1977

Relative lactose intolerance. A clinical study of tube-fed patients.

A relative intolerance of lactose was demonstrated in 14 of 16 patients receiving nasogastric tube feedings following surgery for head or neck carcinoma. Two liquid diets differing only in the presence or absence of lactose, were administered for eight to 20 days per patient in a double-blind crossover study. Increased stool frequency, decreased stool consistency, and more frequent flatulence, borborygmi, and distention were found with the lactose diet, although classic lactose intolerance (plasma glucose rise of less than 26 mg/dl) was indicated in only two patients. Differences between amounts and times of peak rise following the glucose tolerance test and lactose tolerance test for each patient indicated the advisability of locating patients on a continuum of ability to hydrolyze lactose. The results indicate that lactose should be reduced or eliminated from tube-feeding diets to improve patient tolerance and comfort and to reduce diarrhea.

Aged↗
PubMedDate not supplied

Prevalence of primary adult lactose malabsorption in Poland.

Lactose-absorption capacity was examined in 275 apparently healthy Polish adolescents and adults (214 females and 61 males with an average age of 29.1 years) using a field version of the lactose-tolerance test with breath hydrogen determination. In the total group, 172 lactose absorbers (62.5%) and 103 lactose malabsorbers (37.5%) were identified. Reported milk intolerance and symptoms of lactose intolerance were significantly more frequent in lactose malabsorbers. Subdivision according to the birthplaces of the probands' grandparents did not reveal significant regional differences. The unexpectedly high frequency of lactose malabsorption is further evidence for concentric genetic clines of lactase gene frequencies extending from southern Scandinavia, the area with the lowest observed frequencies of selective adult hypolactasia, to the south and the east.

Adolescent↗
PubMed1984

Lactose maldigestion in Ascaris-infected preschool children.

Two studies were conducted to investigate the contribution of Ascaris lumbricoides to lactose maldigestion in preschool children in two different communities in Panama where milk is available as a source of nutrients and the prevalence of Ascaris is known to be high. Both Ascaris-infected and uninfected children were given a standard lactose load and lactose absorption was studied by measuring the rise in plasma glucose in study 1 and by determination of breath hydrogen concentrations at regular intervals after ingestion of the test dose in study 2. All children were tested before anthelmintic treatment with levamisole and 3 wk after therapy. The mean rise in blood glucose from infected (n = 13) children 40 min after the ingestion of lactose was about half of that of the controls (n = 21). After deworming, lactose digestion improved in previously infected children. In study 2, significant differences in breath hydrogen concentrations postmilk ingestion were observed between the Ascaris-infected (n = 47) and the uninfected children (n = 35) before treatment. There was a substantial reduction of breath hydrogen after milk ingestion in the previously infected children after therapy. No differences were observed in breath hydrogen content of the uninfected children during the pre- and posttreatment phases of the study in the lactose tolerance test. These studies provide evidence that infection with Ascaris lumbricoides impairs lactose digestion in preschool children.

Ascariasis↗
PubMed1996

The clinical relevance of lactose malabsorption in irritable bowel syndrome.

OBJECTIVE: The prevalence of lactose malabsorption (LM) in the Caucasian population of northern Europe is estimated to be low. Irritable bowel syndrome (IBS) is a very common diagnosis, and its symptoms are nearly identical to those of LM. Therefore we investigated the prevalence of LM among IBS patients in comparison with healthy volunteers. DESIGN: A double-blind clinical trial compared with healthy controls. SETTING: One out-patient gastroenterology clinic in the Netherlands. PATIENTS: 70 Caucasian IBS patients and 35 healthy volunteers (staff members). METHODS: All 105 underwent hydrogen (H2) breath and blood glucose tests, after an oral intake of 50 grams of lactose. The IBS patients were treated with a lactose-restricted diet for 6 weeks. They completed a lactose intake score before, and a symptom score scored by six separate criteria, before, during and after treatment. RESULTS: In 17 out of 70 (24.3%) IBS patients LM was detected, in comparison with 2 out of 35 (5.7%) controls (P < 0.009). There was no difference in the pre-entry mean lactose intake and symptom score between the LM positive and negative IBS patients. The mean symptom score of the LM positive group showed a marked decrease after 6 weeks of dietary therapy (P < 0.001). CONCLUSION: A substantial number of IBS patients showed a clinically unrecognized lactose malabsorption, which could not be discriminated by symptoms and dietary history, and which can be treated with a lactose-restricted diet. Therefore LM has to be excluded before the diagnosis IBS is made.

Adolescent↗