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At least 811 records · Page 45Linked to original sources
PubMed1983

Effects of lactose on intestinal calcium absorption in normal and lactase-deficient subjects.

The effect of lactose on intestinal calcium absorption was studied in 12 normal-lactase subjects and 7 lactase-deficient subjects. Calcium absorption was compared by using the double isotope technique with or without the presence of an oral load of 50 g of lactose in each subject. The kinetic parameters were measured by the deconvolution method. In the normal lactase group, the lactose prolonged the duration of absorption at a maximum rate and therefore increased the total fractional calcium absorption from 0.224 +/- 0.039 to 0.356 +/- 0.076 (p less than 0.001). In the lactase-deficient subjects, the lactose decreased the total absorption from 0.255 +/- 0.039 to 0.209 +/- 0.032 (p less than 0.005); this effect resulted in a decrease of the maximum absorption rate. There was no significant difference between the two groups when calcium was ingested alone. These results indicate that the effect of lactose on calcium absorption is dependent on intestinal lactase activity.

Adult↗
PubMed1980

[Lactase deficiency in the intestinal mucosa. Demonstration by hydrogen detection in the expired air after lactose loading (author's transl)].

Lactose malabsorption can be demonstrated by detecting hydrogen (H2) in the expired air after oral loading with lactose. A comparative study was carried out on 24 subjects. Following an oral loading dose of lactose, the H2 eliminated during expiration was assayed by gas chromatography, and blood galactose levels were measured. The results showed that the test was reliable, well tolerated and reproductible. However, the method does not measure the amounts of lactase present in the intestinal mucosa. The lactose loading test seems to be valuable for studies on lactose and carbohydrate malabsorption.

Adult↗
PubMed1993

[Lactose digestion and absorption in the jejunum of man: studies using the regional perfusion method].

Continuous jejunal perfusion with 0.1, 1 and 10% lactose solutions was made in 9 patients with good milk tolerance and 25 patients with secondary hypolactasia. In normal tolerance lactose is assimilated in amounts of 30-60% along the 30 cm of the jejunal length. Hypolactasia results in inhibited hydrolysis and absorption of lactose whose activity rapidly diminishes. The phenomenon of substrate lactose induction is demonstrated available both in normal and hypolactasia conditions. In stepwise introduction of lactose in the intestine the tolerance to milk sugar noticeably rises. This fact should be allowed for when conducting enteral feeding.

Adolescent↗
PubMed1993

[Effect of a lactose-free diet on irritable bowel syndrome].

Pathological lactose-H2-breath test is a frequent finding in patients with suspected irritable bowel syndrome. We found it in 33 of 55 patients (60%) with chronic non-specific abdominal symptoms. Follow-up examinations after 15 months (mean) exhibited that lactose-free diet relieved symptoms in 57% of these patients completely or nearly completely. In contrast, only 12% of the patients without lactose malabsorption showed equal amelioration on the various unspecific diets and medications. The lactose-free diet succeeded particularly in young patients and patients with a short history of complaints. Therefore, we recommend lactose-H2-breath test in all patients with suspected irritable bowel syndrome for optimizing therapy.

Adult↗
PubMed1978

The practical significance of lactose intolerance in children.

Lactose intolerance is observed in black and Mexican-American children by age 3 years, and it probably occurs in other non-northern European ethnic groups at a similar age. However, intolerance to the consumption of 250 ml of milk apparently is rarely seen in preadolescents. Current research on the response of adolescents to hydrolyzed lactose milk suggests that the symptoms observed in lactose-intolerant subjects after milk ingestion may be unrelated to lactose or may be mild enough to be of little practical significance. The effects of undigested lactose on nutrient absorption has received little attention, but preliminary data suggest that this is not a problem, except perhaps when overall intakes are marginally adequate.

Adolescent↗
PubMed1999

Comparison of soy-based formulas with lactose and with sucrose in the treatment of acute diarrhea in infants.

OBJECTIVE: To evaluate the effect of feeding infants a soy-based formula with lactose compared with a soy-based formula with sucrose during an acute diarrheal episode. PARTICIPANTS AND METHODS: Two hundred boys, aged 3 to 18 months, who were admitted to the hospital with acute diarrhea and signs of dehydration were randomly assigned to receive a soy-based formula with lactose or sucrose after initial rehydration. Intake and output (stool, urine, and vomit) were measured and recorded every 3 hours until diarrhea resolved. RESULTS: The stool output during the first 24 hours of maintenance therapy, the total stool output during maintenance therapy, and the stool output during the entire illness (measured in grams per kilograms) were significantly lower among patients who received the soy-based formula with sucrose (P<.05, P<.001, and P<.001, respectively) than among patients who received the soy-based formula with lactose. The duration of diarrhea was significantly shorter among patients who received the soy-based formula with sucrose (P<.001). The relative risk of being withdrawn from the study increased to 1.95 (95% confidence interval, 0.65-9.2) and the relative risk of recurrence of dehydration after feeding was initiated increased significantly to 3.49 (95% confidence interval, 1.1-9.6; P<.01) in the group receiving the soy-based formula with lactose. CONCLUSION: During diarrheal episodes, feeding infants a soy-based formula with sucrose has a better outcome (lower stool output, shorter duration of diarrhea, and lower failure rates) than feeding infants a soy-based formula with lactose.

Acute Disease↗
PubMed1998

Highly efficient assimilation of lactose by a metabolically engineered strain of Saccharomyces cerevisiae.

A diploid strain of Saccharomyces cerevisiae able to metabolize lactose with high efficiency has been obtained. Haploid strains of Saccharomyces able to grow on lactose were constructed by cotransformation with two genes of Kluyveromyces lactis required for the utilization of the sugar, LAC4 and LAC12, encoding beta-galactosidase and lactose permease respectively. Both genes were placed under the control of a galactose-inducible promoter and targeted to the rDNA encoding region (RDN1 locus) of the Saccharomyces genome. Lac+ transformants were selected on medium with lactose as the only carbon source. These transformants were mitotically stable, they maintained the Lac+ phenotype after growing in non-selective medium for more than 60 generations, but their growth was slow. We found that this lack of vigour was caused by their genetic background and not by a deficient expression of the heterologous genes. Therefore, their performance could be improved by crossing with a wild-type strain. Among the offspring of the crosses, two strains of opposite mating type were selected and mated to obtain a fast-growing Lac+ diploid. This diploid strain showed the typical fermentative behaviour of S. cerevisiae when it was grown in aerated liquid medium with glucose. In lactose medium, it exhibited a respiro-fermentative metabolism similar to that of K. lactis, with low ethanol production and high biomass yield.

Biomass↗
PubMed1994

The role of transmembrane domain III in the lactose permease of Escherichia coli.

Deletion of putative transmembrane helix III from the lactose permease of Escherichia coli results in complete loss of transport activity. Similarly, replacement of this region en bloc with 23 contiguous Ala, Leu, or Phe residues abolishes active lactose transport. The observations suggest that helix III may contain functionally important residues; therefore, this region was subjected to Cys-scanning mutagenesis. Using a functional mutant devoid of Cys residues (C-less permease) each residue from Tyr 75 to Leu 99 was individually replaced with Cys. Twenty-one of the 25 mutants accumulate lactose to > 70% of the steady-state exhibited by C-less permease, and an additional 3 mutants transport to lower, but significant levels (40-60% of C-less). Cys replacement for Leu 76 results in low transport activity (18% of C-less). However, when placed in the wild-type background, mutant Leu 76-->Cys exhibits highly significant rates of transport (55% of wild type) and steady-state levels of lactose accumulation (65% of wild type). Immunoblots reveal that the mutants are inserted into the membrane at concentrations comparable to wild type. Studies with N-ethylmaleimide show that mutant Gly 96-->Cys is rapidly inactivated, whereas the other single-Cys mutants are not altered significantly by the alkylating agent. Moreover, the rate of inactivation of Gly 96-->Cys permease is enhanced at least 2-fold in the presence of beta-galactopyranosyl 1-thio-beta, D-galactopyranoside. The observations demonstrate that although no residue per se appears to be essential, structural properties of helix III are important for active lactose transport.

Amino Acid Sequence↗
PubMed2001

Enhanced expression of cytochrome P450s from lac-based plasmids using lactose as the inducer.

The cytochrome P450 expression systems used in Escherichia coli are highly regulated and involve the use of the lac repressor to control expression. Induction in these systems utilizes the nonmetabolizable analog of lactose, isopropyl-beta-D-thiogalactopyranoside (IPTG), which is the most expensive compound required for an E. coli expression system. To determine if the natural inducer lactose could be used to induce cytochrome P450 expression we examined the expression of three P450 enzymes in E. coli using two different expression systems, pTrc99A and the T7-based PET22b vector. For both systems lactose was found to induce expression of active P450 to concentrations that exceeded the levels achieved with IPTG. A 20-liter fermentation of a P450 expression system in the pTrc plasmid in which lactose was used as the inducer resulted in 2.4 micromol P450/liter, with a total yield of 2 g of cytochrome P450. The use of lactose for protein expression in E. coli should be broadly useful for the inexpensive, large-scale production of heterologous proteins in E. coli.

Cytochrome P-450 Enzyme System↗
PubMed1994

Carbohydrate binding activities of Bradyrhizobium japonicum: IV. Effect of lactose and flavones on the expression of the lectin, BJ38.

BJ38 is a galactose/lactose-specific lectin (M(r) approximately 38,000) found at one pole of Bradyrhizobium japonicum. It has been implicated in mediating the adhesion of the bacteria to soybean roots, leading to the establishment of a nitrogen-fixing symbiosis. When the ligand lactose is added to cultures of the bacteria for at least 1 h prior to harvesting the cells for BJ38 isolation, the yield of the protein was found to be elevated in a dose-dependent fashion. Half maximal stimulation was observed at approximately 50 microM; the effect was saturated at approximately 1 mM, where a 10-fold higher yield of BJ38 was obtained. Saccharides with a lower affinity for BJ38 than lactose yielded a correspondingly smaller induction effect when compared at a concentration of 1 mM. The higher level of BJ38 induced by lactose is also manifested by an elevated amount of BJ38 detectable at the cell surface and by a higher number of B. japonicum cells adsorbed onto soybean cells. Surprisingly, the induction of BJ38 expression seen with lactose was also observed with certain, but not all, flavonoids that induce the nod genes of the bacteria; genistein mimicked the induction observed with lactose, whereas luteolin failed to stimulate BJ38 production.

Carbohydrate Metabolism↗
PubMed1987

Blood glucose and plasma insulin responses to fat-free milk and low-lactose fat-free milk in young type 1 diabetics.

The blood glucose and plasma insulin responses to test milk samples were studied in eight insulin-dependent diabetics. After an overnight fast, the subjects (aged 20-45 years) were given a breakfast containing two Weetabix biscuits (20 g carbohydrate) with 500 ml of either regular (S) fat-free milk (25 g lactose) or 500 ml of a new low-lactose (D) fat-free milk (3.75 g lactose and 4.25 g fructose). The regular morning insulin dose was omitted. Mean basal plasma glucose level was slightly higher before S milk (11.4 vs. 10.1 mmol/l). The peak increment in plasma glucose was higher in S milk (9.4 vs. 6.6 mmol/l). The rise was 83% above basal (S) vs. 65% (D). Although the final mean plasma glucose concentration was not significantly higher 3 h after S milk compared with D milk (17.9 vs. 14.3 mmol/l) the incremental area under the plasma glucose curve was much greater (p less than 0.001) with S milk than with D milk (1266 +/- 295 units vs. 909 +/- 242 units). No galactose was detectable in any sample and there was no difference in plasma beta-hydroxybutyrate levels. The results suggest that the low-lactose fat-free milk (D) may be suitable for diabetic diets and weight reducing diets due to the lower contribution of energy. The results suggest that fat-free milk does not exert a fast action on blood glucose concentration and therefore fat-free milk and especially low-lactose fat-free milk may also prove to be suitable for diabetic diets.

Adult↗
PubMed2004

Improved xylanase production by Trichoderma reesei grown on L-arabinose and lactose or D-glucose mixtures.

Trichoderma reesei Rut C-30 was grown on eight different natural or rare aldopentoses as the main carbon source and on mixtures of an aldopentose with D-glucose or lactose. The fungal cells consumed all aldopentoses tested, except L-xylose and L-ribose. The highest total xylanase and cellulase activities were achieved when cells were grown on L-arabinose as the main carbon source. The total xylanase activity produced by cells grown on L-arabinose was even higher than that produced by cells grown on an equal amount of lactose. In co-metabolism of D-glucose (15 g l(-1)) and L-arabinose (5 g l(-1)), the total volumetric and specific xylanase productivities were improved (derepressed) approximately 23- and 18-fold, respectively, compared to a cultivation on only D-glucose (20 g l(-1)). In a similar experiment, in which cells were grown on a mixture of lactose and L-arabinose, the xylanase productivity was approximately doubled, compared to a cultivation on only lactose. The cellulase productivities, however, were not improved by the addition of L-arabinose. Compared with a typical industrial fungal enzyme production process with lactose as the main carbon source, better volumetric and specific xylanase productivities were achieved both on a lactose/arabinose mixture and on a glucose/arabinose mixture.

Arabinose↗
PubMed2006

Cellulase production by Penicillium echinulatum on lactose.

The inducer effect of lactose on cellulase activity in Penicillium echinulatum 9A02S1 was studied. Submerged cultivation was performed using different concentrations of lactose and cellulose, in which the pH, mycelial mass, soluble proteins, filter paper activity (FPA), and activity of beta-glucosidases were measured. The cultures containing lactose only presented low FPAs (0.1 FPU/ml). The cultures with associated cellulose and lactose and those containing cellulose only presented similar enzymatic activities (1.5 FPU/ml), suggesting the possibility of up to 75% reduction in the cellulose concentration. In relation to the beta-glucosidases, increasing the lactose/cellulose ratio results in a proportional increase of enzymatic activity. In the cultures using both inducers, there is a longer duration of the acid phase in relation to treatments using only cellulose or lactose, indicating diauxia and catabolic repression.

Biomass↗
PubMed2005

Fed-batch fermentation for production of Kluyveromyces marxianus FII 510700 cultivated on a lactose-based medium.

A strain of Kluyveromyces marxianus was grown in batch culture in lactose-based media at varying initial lactose concentrations (10-60 g L(-1)) at 30 degrees C, pH 5.0, dissolved oxygen concentrations greater than 20%. Increasing the concentration of mineral salts three-fold at 40 g L(-1) and 60 g L(-1) initial lactose concentration showed only a small increase in the yield of biomass, from 0.38 g g(-1) to 0.41 g g(-1), indicating that the initial batch cultures were not significantly nutrient- (mineral salts)-limited. A relatively high biomass concentration (105 g L(-1)) was obtained in fed-batch culture following extended lactose feeding. An average specific growth rate (0.27 h(-1)), biomass yield (0.38 g g(-1)) and overall productivity (2.9 g L(-1) h(-1)) were obtained for these fed-batch conditions. This fed-batch protocol provides a strategy for achieving relatively high concentrations and productivities of K. marxianus on other lactose-based substrate streams (e.g., whey) from the dairy industry.

Culture Media↗
PubMed1981

Lactose transport in Escherichia coli cells. Dependence of kinetic parameters on the transmembrane electrical potential difference.

We determine the kinetic parameters V and KT of lactose transport in Escherichia coli cells as a function of the electrical potential difference (delta psi) at pH 7.3 and delta pH = 0. We report that transport occurs simultaneously via two components: a component which exhibits a high KT (larger than 10 mM) and whose contribution is independent of delta psi, a component which exhibits a low KT independent of delta psi (0.5 mM) but whose V increases drastically with increasing delta psi. We associate these components of lactose transport with facilitated diffusion and active transport, respectively. We analyze the dependence upon delta psi of KT and V of the active transport component in terms of a mathematical kinetic model developed by Geck and Heinz (Geck, P. and Heinz, E. (1976) Biochim. Biophys. Acta 443, 49-63). We show that within the framework of this model, the analysis of our data indicates that active transport of lactose takes place with a H+/lactose stoichiometry greater than 1, and that the lac carrier in the absence of bound solutes (lactose and proton(s) is electrically neutral. On the other hand, our data relative to facilitated diffusion tend to indicate that lactose transport via this mechanism is accompanied by a H+/lactose stoichiometry smaller than that of active transport. We discuss various implications which result from the existence of H+/lactose stoichiometry different for active transport and facilitated diffusion.

Biological Transport, Active↗
PubMed1981

Physical and chemical characterization of the major lactose-blockable lectin activity from fetal calf skeletal muscle.

The lactose-blockable lectin activity from fetal calf skeletal muscle has been purified to apparent homogeneity. The purification entails differential centrifugation, ammonium sulfate precipitation, asialofetuin affinity chromatography with a lactose gradient and ion-exchange chromatography on DEAE-cellulose. In the last step, the activity is resolved into a major and minor species, designated ion-exchange-purified lectins I and II, respectively. Both lectin activities are reversibly inhibited by lactose and appear as single bands with identical mobilities on SDS-polyacrylamide gel electrophoresis. Lectin II was not obtained in sufficient quantities for further characterization. Lectin I is characterized by a functional requirement for reducing agents and sensitivity to N-ethylmaleimide, which suggests a role for an essential thiol in its activity. Subunit molecular weight determinations by SDS-polyacrylamide gel electrophoresis (12 000 +/- 1 000) and by gel filtration in 6 M guanidine . HCl (13 000 +/- 1 000), when compared with that obtained under native conditions on Bio-Rad P-60 gels (27 000 +/- 2 000), suggest a true Mr of 25 000 +/- 3 000 for the dimeric molecule. Amino acid composition data, when fitted to this molecular weight, lead to the tentative conclusion that the intact dimer is composed of two very similar but compositionally non-identical chains, designated by alpha and beta. While the only detectable N-terminal amino acid is tryptophan, the isoelectric focusing pattern of lectin I supports this heterodimeric structure. In addition, a lactose-sensitive hemagglutinating activity which can be separated from the lactose-blockade activity by affinity chromatography was also observed.

Amino Acids↗
PubMed1992

Synthesis and characterization of 6-O-beta-lactosyl-alpha,beta-lactoses, 1-O-(6-O-beta-lactosyl-beta-lactosyl)-(R,S)-glycerols, and 4,6-di-O-beta-D-galactopyranosyl-alpha,beta-D-glucoses.

1,2,3,2',3',4',6'-Hepta-O-acetyl-beta-lactose (4) was coupled with 2,3,6,2',3',4',6'-hepta-O-acetyl-alpha-lactosyl bromide (7) in the presence of Hg(CN)2 to afford 1,2,3,2',3',4',6'-hepta-O-acetyl-6-O-(2,3,6,2',3',4',6'-hepta-O-acetyl-b eta- lactosyl)-beta-lactose (11) which, upon O-deacetylation, gave 6-O-beta-lactosyl-alpha,beta-lactoses (64% from 4). In contrast, the reaction of 7 with benzyl 2,3,2',3',4',6'-hexa-O-acetyl-beta-lactoside in the presence of Hg(CN)2 produced 3,6,2',3',4',6'-hexa-O-acetyl-1,2-O- (2,3,2',3',4',6'-hexa-O-acetyl-1-O-benzyl-beta-lactos-6-yl orthoacetyl)-alpha-lactose (63%) and 3,6,2',3',4',6'-hexa-O-acetyl-1,2-O-(1- cyanoethylidene)-alpha-lactose (27%). The glycosidation of 4 using 2,3,4,6-tetra-O-acetyl-alpha-D-galactopyranosyl bromide in the presence of Hg(CN)2 afforded, after deprotection, 4,6-di-O-beta-D-galactopyranosyl-alpha,beta-D-glucoses (66%). The reaction of 11 with 1,2-di-O-benzyl-(R,S)-glycerols and trimethylsilyl trifluoromethanesulfonate yielded, after deprotection, 1-O-(6-O-beta-lactosyl-beta-lactosyl)-(R,S)-glycerols (18%). Under the same coupling conditions 11 reacted with 2-O-benzylglycerol to form 3-O-acetyl-2-O-benzyl-1-O-[2',3',4',6'-hexa-O-acetyl-6-O-(2,3,6,2',3',4' ,6'- hepta-O-acetyl-beta-lactosyl)-beta-lactosyl]-(R,S)-glycerols (16%).

Asialoglycoprotein Receptor↗
PubMed1983

The lactose carrier of Escherichia coli functionally incorporated in Rhodopseudomonas sphaeroides obeys the regulatory conditions of the phototrophic bacterium.

Rhodopseudomonas sphaeroides was provided with the ability to transport lactose via conjugation with a strain of Escherichia coli bearing a plasmid containing the lactose operon (including the lac Y gene, coding for the lactose carrier or M protein) and subsequent expression of the lac operon in Rps. sphaeroides (Nano, F.E. and Kaplan, S. submitted). The initial rate of lactose transport in Rps. sphaeroides was studied as a function of the light intensity and the magnitude of the proton-motive force. The results demonstrate that lactose transport is regulated by the rate of cyclic electron transfer in the same way as the endogenous transport systems.

Alanine↗