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At least 973 records · Page 54Linked to original sources
PubMed1986

Isolation and characterization of lactose-binding lectins from the venoms of the snakes Lachesis muta and Dendroaspis jamesonii.

Two lectins have been isolated: one from the venom of Lachesis muta (bushmaster lectin) and one from Dendroaspis jamesonii venom (Jameson's mamba lectin). The lectin from bushmaster venom (BML) is similar to the lactose-binding lectins previously isolated from snake venoms (Gartner et al. (1980) FEBS Lett. 117, 13-16; Gartner & Ogilvie (1984) Biochem. J. 224, 301-307) in that it is calcium-dependent, lactose inhibitable, and is a dimer of molecular weight 28,000. In contrast, the lactose-blockable lectin from Jameson's mamba venom (JML) has an apparent molecular weight of 26,000 and agglutinates erythrocytes in the presence of EDTA. The absorption spectra of BML were affected by the binding of calcium, or calcium and lactose to the lectin. However, JML spectra were not affected by these conditions. While the hemagglutination activity of each of the previously described lactose-binding snake venom lectins is inhibited by reducing agent, the activities of BML and JML are not affected by reducing agent. Antiserum against bushmaster lectin cross-reacts with thrombolectin, cottonmouth lectin (CML), rattlesnake lectin (RSL), and copperhead lectin (CuHL) but not lectin from Jameson's mamba venom. This evidence plus a comparison of atomic absorption spectra, isoelectric points and amino acid analyses of the lectins demonstrate that JML and BML are different from thrombolectin, CML, RSL, and CuHL.

Amino Acids↗
PubMed1986

Limited proteolysis of lactose permease from Escherichia coli.

Escherichia coli lactose permease (also referred to as lactose carrier) is an integral protein of the cytoplasmic membrane. Using lactose permease either radiolabeled biosynthetically in plasmid-bearing E. coli minicells or radioalkylated post-synthetically by chemical modification, we have determined sites on the membrane-bound protein accessible to proteolytic attack and we have characterized several high-molecular-mass products. The most prominent polypeptide obtained from lactose permease radiolabeled biosynthetically is observed after digestion with different proteases. The fragment produced by thermolysin was shown to contain the intact N-terminus and to extend into the region around amino acid residue 140 which, according to secondary structure models, is presumed to be less tightly folded than the rest of the molecule. Evidence is presented that the corresponding fragments obtained after digestion with several other proteases also originate from the N-terminal part of the protein. This N-terminal segment of the lactose carrier is resistant to proteolytic digestion even in the presence of non-ionic detergents and it may represent a tightly folded domain. Additional proteolytic cleavage sites located C-terminal of the Cys148 residue can be inferred.

Amino Acid Sequence↗
PubMed1981

Conjugal Transfer of Lactose-Fermenting Ability Among Streptococcus cremoris and Streptococcus lactis Strains.

Streptococcus cremoris C3 was found to transfer lactose-fermenting ability to LM2301, a Streptococcus lactis C2 lactose-negative streptomycin-resistant (Lac Str) derivative which is devoid of plasmid deoxyribonucleic acid (DNA); to LM3302, a Lac erythromycin-resistant (Ery) derivative of S. lactis ML3; and to BC102, an S. cremoris B(1) Lac Ery derivative which is devoid of plasmid DNA. S. cremoris strains R1, EB(7), and Z8 were able to transfer lactose-fermenting ability to LM3302 in solid-surface matings. Transduction and transformation were ruled out as mechanisms of genetic transfer. Chloroform treatment of donor cells prevented the appearance of recombinant clones, indicating that viable cell-to-cell contact was responsible for genetic transfer. Transfer of plasmid DNA was confirmed by agarose gel electrophoresis. Transconjugants recovered from EB(7) and Z8 matings with LM3302 exhibited plasmid sizes not observed in the donor strains. Transconjugants recovered from R1, EB(7), and Z8 matings with LM3302 were able to donate lactose-fermenting ability at a high frequency to LM2301. In S. cremoris R1, EB(7), and Z8 matings with LM2301, streptomycin resistance was transferred from LM2301 to the S. cremoris strains. The results confirm genetic transfer resembling conjugation between S. cremoris and S. lactis strains and present presumptive evidence for plasmid linkage of lactose metabolism in S. cremoris.

Journal Article↗
PubMed1986

Construction of lactose-assimilating and high-ethanol-producing yeasts by protoplast fusion.

The availability of a yeast strain which is capable of fermenting lactose and at the same time is tolerant to high concentrations of ethanol would be useful for the production of ethanol from lactose. Kluyveromyces fragilis is capable of fermenting lactose, but it is not as tolerant as Saccharomyces cerevisiae to high concentrations of ethanol. In this study, we have used the protoplast fusion technique to construct hybrids between auxotrophic strains of S. cerevisiae having high ethanol tolerance and an auxotrophic strain of lactose-fermenting K. fragilis isolated by ethyl methanesulfonate mutagenesis. The fusants obtained were prototrophic and capable of assimilating lactose and producing ethanol in excess of 13% (vol/vol). The complementation frequency of fusion was about 0.7%. Formation of fusants was confirmed by the increased amount of chromosomal DNA per cell. Fusants contained 8 x 10 to 16 x 10 mug of DNA per cell as compared with about 4 x 10 mug of DNA per cell for the parental strains, suggesting that multiple fusions had taken place.

Journal Article↗
PubMed1987

Properties of Lactose Plasmid pLY101 in Lactobacillus casei.

A starter strain, Lactobacillus casei C257, was found to carry a lactose plasmid, pLY101. Restriction mapping showed that pLY101 DNA was 68.2 kilobases long. Since a non-lactose-utilizing variant of C257, MSK248, lost phospho-beta-galactosidase (P-beta-gal) activity and pLY101 DNA had a sequence(s) homologous to the streptococcal fragment including a P-beta-gal gene, pLY101 is likely to encode a P-beta-gal gene required for lactose metabolism in C257. MSK248 grew in galactose medium at a rate identical to that of C257 and retained phosphoenolpyruvate-dependent phosphotransferase system activity for lactose similar to that of C257. Therefore, the C257 chromosome appears to encode a complete set of genes for the lactose-phosphotransferase system and the predominant galactose metabolic pathway in C257. pLY101 DNA had a sequence homologous to a lactobacillus insertion sequence, ISL1, which mapped more than 12 kilobases from the sequence homologous to the streptococcal P-beta-gal fragment.

Journal Article↗
PubMed1996

Development and characterization of lactose-positive pediococcus species for milk fermentation.

Bacteriophages against Streptococcus thermophilus are a growing problem in the Italian cheese industry. One possible control method involves replacing S. thermophilus in mozzarella starter blends with lactic acid bacteria from a different genus or species. In this study, we evaluated lactose-positive pediococci for this application. Because we could not identify any commercially available pediococci with fast acid-producing ability in milk, we transformed Pediococcus pentosaceus ATCC 25744, P. pentosaceus ATCC 25745, and Pediococcus acidilactici ATCC 12697 by electroporation with pPN-1, a 35-kb Lactococcus lactis lactose plasmid. Transformants of P. pentosaceus ATCC 25745 and P. acidilactici ATCC 12697 were then used to examine lactose-positive pediococci for properties related to milk fermentation. Both transformants rapidly produced acid and efficiently retained pPN-1 in lactose broth, and neither bacterium was attacked by bacteriophages in whey collected from commercial cheese facilities. Paired starter combinations of Pediococcus spp. and Lactobacillus helveticus LH100 exhibited synergistic pH reduction in milk, and small-scale cheese trials showed that these cultures could be used to manufacture part-skim mozzarella cheese. Results demonstrate that lactose-positive pediococci have potential as replacement cocci for S. thermophilus in Italian cheese starter blends and may facilitate development of new strain rotation schemes to combat S. thermophilus bacteriophage problems in mozzarella cheese plants.

Journal Article↗
PubMed1996

The lactose transporter in Leuconostoc lactis is a new member of the LacS subfamily of galactoside-pentose-hexuronide translocators.

The gene encoding the lactose transport protein (lacS) of Leuconostoc lactis NZ6009 has been cloned from its native lactose plasmid, pNZ63, by functional complementation of lactose permease-deficient Escherichia coli mutants. Nucleotide sequence analysis revealed an open reading frame with the capacity to encode a protein of 639 amino acids which had limited but significant identity to the lactose transport carriers (LacS) of Streptococcus thermophilus (34.5%) and Lactobacillus bulgaricus (35.6%). This similarity was present both in the amino-terminal hydrophobic carrier domain, which is homologous to the E. coli melibiose transporter, and in the carboxy-terminal enzyme IIA-like regulatory domain. The flanking regions of DNA surrounding lacS were also sequenced. Preceding the lacS gene was a small open reading frame in the same orientation encoding a deduced 95-amino-acid protein with a sequence similar to the amino-terminal portion of beta-galactosidase I from Bacillus stearothermophilus. The lacS gene was separated from the downstream beta-galactosidase genes (lacLM) by 2 kb of DNA containing an IS3-like insertion sequence, which is a novel arrangement for lac genes in comparison with that in other lactic acid bacteria. The lacS gene was cloned in an E. coli-Streptococcus shuttle vector and was expressed both in a lacS deletion derivative of S. thermophilus and in a pNZ63-cured strain, L. lactis NZ6091. The role of the LacS protein was confirmed by uptake assays in which substantial uptake of radiolabeled lactose or galactose was observed with L. lactis or S. thermophilus plasmids harboring an intact lacS gene. Furthermore, galactose uptake was observed in NZ6091, suggesting the presence of at least one more transport system for galactose in L. lactis.

Amino Acid Sequence↗
PubMed1998

Influence of reduced water activity on lactose metabolism by lactococcus lactis subsp. cremoris At different pH values

The influence of reduced water activity (aw) on lactose metabolism by Lactococcus lactis subsp. cremoris 2254 and 2272 was studied at different pH values. In control incubations (aw, 0.99) with nongrowing cells in pH-controlled phosphate buffer, the levels of carbon recovered as L-(+)-lactate were 92% at pH 6.1 and 5.3 and 78% at pH 4.5. However, the levels of recovery decreased to approximately 50% at all pH values tested when the aw was 0.88 (with glycerol as the humectant). When growing cells in broth controlled at pH 6.3 were used, a reduction in the aw from 0.99 to 0.96 resulted in a decrease in the level of lactose carbon recovered as L-(+)-lactate from 100 to 71%. Low levels of L-(+)-lactate carbon recovery (<50%) were also observed with cells resuspended in pH-uncontrolled reconstituted skim milk at aw values of 0.99 and 0. 87 and in young cheese curds. The missing lactose carbon could not be accounted for by acetate, ethanol, formate, acetaldehyde, or pyruvate. Attempts were made to determine where the missing lactose carbon was diverted to under the stress conditions used. Some of the missing lactose carbon was recovered as galactose (0.1 to 2.5 mM) in culture supernatants. Decreasing either the aw or the pH resulted in increased galactose accumulation by nongrowing cells; adjusting both environmental factors together potentiated the effect. The sensitivities of the two lactococcal strains tested were different; strain 2272 was more prone to accumulate galactose under stress conditions. A methyl pentose(s) and additional galactose were found in acid-hydrolyzed supernatants from cultures containing both growing and nongrowing cells, indicating that a saccharide(s) rich in these components was formed by lactococci under low-aw and low-pH stress conditions.

Journal Article↗
PubMed1988

Truncated forms of Escherichia coli lactose permease: models for study of biosynthesis and membrane insertion.

Using in vitro DNA manipulations, we constructed different lacY alleles encoding mutant proteins of the Escherichia coli lactose carrier. With respect to structural models developed for lactose permease, the truncated polypeptides represent model systems containing approximately one, two, four, and five of the N-terminal membrane-spanning alpha-helices. In addition, a protein carrying a deletion of predicted helices 3 and 4 was obtained. The different proteins were radiolabeled in plasmid-bearing E. coli minicells and were found to be stably integrated into the lipid bilayer. The truncated polypeptides of 50, 71, 143, and 174 N-terminal amino acid residues resembled the wild-type protein in their solubilization characteristics, whereas the mutant protein carrying an internal deletion of amino acid residues 72 to 142 of the lactose carrier behaved differently. Minicell membrane vesicles containing truncated proteins comprising amino acid residues 1 to 143 or 1 to 174 were subjected to limited proteolysis. Upon digestion with proteases of different specificities, the same characteristic fragment that was also produced from the membrane-associated wild-type protein was found to accumulate under these conditions. It has previously been shown to contain the intact N terminus of lactose permease. This supports the idea of an independent folding and membrane insertion of this segment even in the absence of the C-terminal part of the molecule. The results suggest that the N-terminal region of the lactose permease represents a well-defined structural domain.

Alleles↗
PubMedDate not supplied

[Nutritional status and breath hydrogen test with lactose and lactulose in Terena Indian children].

OBJECTIVE: To evaluate the nutritional status, absorption and tolerance of lactose and the occurrence of small-bowel bacterial overgrowth. METHODS: A cross-sectional study including all 264 Terena Indian children younger than 10 years from two tribes (Limão Verde and Córrego Seco) in Mato Grosso do Sul. The nutritional status was assessed based upon weight and height, using NCHS data as reference. The breath hydrogen test after an oral lactose (18 g) administration was used for evaluation of lactose absorption and tolerance. The occurrence of bacterial overgrowth was evaluated using the breath hydrogen test after the administration of lactulose (5 g). RESULTS: The median z scores of weight-for-age, weight-for-height and height-for-age were, respectively, in infants under 1 year (n=34): -0.66, +0.60 and -0.85. Between 1 and 5 years (n=111), the values were: -0.50, +0.28 and -1.17. Between 5 and 10 years (n=119), these anthropometric values were, respectively: -0.09, +0.50 and -0.60. Deficient lactose absorption or malabsorption was verified only after the fourth year of age in 89.3% of the 197 evaluated children. Lactose intolerance was found in 37.1% of them. Small-bowel overgrowth was detected in 11.5% of the Terena Indian children (n=252). CONCLUSIONS: The prevalence of recent malnutrition was low, but the median height-for-age was lower than the NCHS reference. The prevalence of ontogenetic lactase deficiency was high. Bacterial overgrowth may be considered as evidence of the occurrence of nonsymptomatic environmental enteropathy in Terena Indian children.

English Abstract↗
PubMed2001

Use of Staphylococcus aureus 6-P-beta-galactosidase and GFP as fusion partners for lactose-specific IIC domain from Staphylococcus aureus.

The hydrophilic part of membrane proteins plays an important role in the formation of 3D crystals. The construction of fusion proteins using well crystallizing proteins as fusion partners is a possibility to increase the hydrophilic part of membrane proteins lacking large hydrophilic domains. These fusion proteins might be easier to crystallize. Two bifunctional fusion proteins containing the membrane-bound, lactose-specific enzyme IIC domain of the lactose transporter (IICB(lac)) from S. aureus as N-terminal fusion partner were constructed by gene fusion. The C-terminal fusion partners were S. aureus 6-P-beta-Galactosidase and GFP, respectively. Both proteins were overexpressed in E. coli, purified to homogeneity and kinetically characterized: In the presence of the components of the lactose phosphotransferase system of S. aureus, the hybrid proteins phosphorylated their substrates, indicating that the fusion partners are sufficiently flexibly linked to allow the interaction of the IIC(lac) domain with the IIB(lac) domain of the lactose transporter. The activity of the 6-P-beta-Galactosidase as well as the fluorescence of GFP were preserved in the fusion proteins. The Vmax values determined for the IIC domain in the fusion proteins were dramatically reduced compared with the values determined for the separate IIC(lac) domain and the complete lactose transporter (IICB(lac)). The Km values were only slightly increased indicating that the Vmax values are much more influenced by the fusion than the substrate affinities. The substrate affinity and the Vmax value determined for the GFP-fused IIC(lac) domain are higher than for the 6-P-beta-Galactosidase-fused IIC(lac). The results suggest that the fusion with GFP enables a better interaction with the IIB(lac) domain than the fusion with 6-P-beta-Galactosidase. Moreover, the GFP-fused IIC(lac) domain proved to be more stable than the 6-P-beta-Galactosidase fusion protein.

Amino Acid Sequence↗
PubMedDate not supplied

[Lactose malabsorption in children and adolescents: diagnosis through breath hydrogen test using cow milk].

OBJECTIVE: To determine the prevalence of lactose malabsorption and its association with skin color and age in children and teenagers attending public schools in Porto Alegre, Brazil. METHODS: A cross-sectional study was performed with 225 subjects between 8 and 18 years attending two public schools in Porto Alegre, Brazil. Patients were randomly selected. Subjects were classified according to skin color (white and non-white) and age group (8 to 12 and 13 to 18 years). Lactose malabsorption was diagnosed using the breath hydrogen test after ingestion of 250 ml of whole cow milk. The test lasted for 3 hours, with collections after fasting and 60, 120, and 180 minutes after milk ingestion. Malabsorption was determined in the presence of increase of > or =20 ppm in hydrogen concentration regarding the basal levels. RESULTS: Two-hundred and twenty-five students were studied, with a mean age +/- standard deviation of 12.2 +/- 2.0 years. The subjects consisted of 134 females (59.6%); 154 white (68.4%); and 71 nonwhite. Lactose malabsorption was observed in 19/225 cases (8.4%). It was diagnosed in 8/154 white patients (5.2%) and in 11/71 non-white patients (15.5%) (p=0.02). Regarding the age group, we found 15/143 cases of malabsorption in students between 8 and 12 years (10.5%), and 4/82 cases in students between 13 and 18 years (4.9%) (p=0.227). CONCLUSIONS: The prevalence of lactose malabsorption in students attending public schools in Porto Alegre is significant, especially if we consider that the physiological doses (250 ml of milk) were used for diagnosis. The malabsorption rate was higher among non-white children, which confirms the influence of race on primary adult type hypolactasia. No association was observed between lactose malabsorption and age group.

English Abstract↗
PubMed1984

The phospholipid requirement for activity of the lactose carrier of Escherichia coli.

The transport activity of the lactose carrier of Escherichia coli has been reconstituted in proteoliposomes composed of different phospholipids. The maximal activity was observed with the natural E. coli lipid as well as mixtures containing phosphatidylethanolamine or phosphatidylserine. Phosphatidylcholine or mixtures of phosphatidylcholine with phosphatidylglycerol, phosphatidic acid, or cardiolipin showed low activity. The lactose carrier reconstituted with amino phospholipids of increasing degrees of methylation (dioleoylphosphatidylethanolamine, dioleoylmonomethylphosphatidylethanolamine, dioleoyldimethylphosphatidylethanolamine, and dioleoylphosphatidylcholine) revealed a progressive decrease in both counterflow and proton motive force-driven lactose uptake activities. Trinitrophenylation of phosphatidylethanolamine in the E. coli proteoliposomes resulted in a marked reduction in lactose carrier activity. Partial restitution of transport activity was obtained by detergent extraction of the carrier from these inactive proteoliposomes and reconstitution of the carrier into proteoliposomes containing normal E. coli lipid. These results suggest that the amino group of the amino phospholipids (e.g. phosphatidylethanolamine and phosphatidylserine) is required for the full function of the lactose carrier from E. coli.

Escherichia coli↗
PubMed1981

Purification and reconstitution of functional lactose carrier from Escherichia coli.

The lactose carrier protein of Escherichia coli was purified by a simple procedure employing differential solubilization and ion-exchange chromatography and reconstituted into liposomes by octylglucoside dilution. The proteoliposomes exhibited both membrane potential-driven lactose transport and lactose counterflow. Furthermore, the purified protein was identified as the product of the lac y gene. These and other results demonstrate that the lactose carrier is the only polypeptide species essential for energy-coupled lactose transport and counterflow.

Amino Acids↗
PubMed1997

Lactose intolerance following antithyroid drug medications.

We recently observed 2 lactase-deficient women with Graves' disease who consistently developed severe diarrhea after ingestion of thionamide (methimazole and propylthiouracil) tablets containing lactose as carrier. The strict temporal relationship between ingestion of lactose-containing tablets and appearance of intestinal symptoms, as well as the absence of side effects following ingestion of methimazole tablets without lactose as carrier, provided the clue for the diagnosis. To our knowledge, severe diarrhea resulting from carrier lactose has not been previously reported for antithyroid drugs, and should be considered in occasional cases of patients with gastrointestinal symptoms on thionamide therapy.

Adult↗
PubMed2005

Lactose hydrogen breath test in Giardia lamblia-positive patients.

The study was conducted in 54 adult patients with Giardia lamblia infection and 54 adult controls to detect lactose maldigestion employing the noninvasive lactose hydrogen breath test. Forty of 54 (74%) patients with Giardia lamblia and 24 of 54 (44.4%) controls showed lactose maldigestion (P < 0.01). In conclusion, this study shows that the frequency of lactose maldigestion is significantly higher in adult Indians suffering from Giardia lamblia infection compared to healthy individuals.

Adult↗
PubMed1978

Breath hydrogen concentrations after oral lactose and lactulose in tropical malabsorption and adult hypolactasia.

Thirty-six hospital in-patients in London had breath-hydrogen concentrations measured after 50 g lactose were given orally; in 23 or them serial blood glucose concentrations were also estimated. Eight had tropical malabsorption (TM), 14 were Europeans with no detectable disease (normal group) and 14 who also had no detectable disease, were from ethnic groups known to have a very high incidence of genetically determined adult hypolactasia (hl). In 21 of them breath-hydrogen concentrations were also measured after 33.5 g of lactulose were given orally. There was a good inverse correlation between breath-hydrogen production and blood-glucose rise after lactose. Correlations between the first appearance of hydrogen (T) and the area under the hydrogen curve between 0 and 120 min (A) were inversely significant both for lactose and lactulose. Mean T was earlier and mean A greater for lactose compared with lactulose. Correlation between individual values for A after lactase and after lactulose was significant. Indirect measurements of lactase are of no value in either detecting or assessing the severity of TM; that is largely due to the very high incidence of HL in individuals exposed to that disease.

Adult↗
PubMed1986

Failure of lactose-restricted diets to prevent radiation-induced diarrhea in patients undergoing whole pelvis irradiation.

Sixty-four patients were randomized prior to pelvic radiotherapy into one of three dietary groups: the control group maintained a regular diet except that they drank at least 480 cc of milk daily; the lactose-restricted group was placed on a lactose-restricted diet; and the lactase group drank at least 480 cc of milk with lactase enzyme added to hydrolyze 90% of the lactose. The patients kept records of their stool frequency and the number of diphenoxylate tablets required to control their diarrhea during a 5 week course of standard whole pelvis irradiation. The data does not support the concept that one of the mechanisms of radiation-induced diarrhea associated with pelvic irradiation is a reduction the ability of the intestine to hydrolyze ingested lactose due to the effect of the radiation on the small intestine. There was not a significant difference in stool frequency or diphenoxylate usage among the dietary groups.

Animals↗