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At least 883 records · Page 49Linked to original sources
PubMed1992

Short-term polycose substitution for lactose reduces calcium absorption in healthy term babies.

A vitamin D-independent paracellular and not saturable mechanism important for intestinal calcium absorption turned out to be less effective in lactose-free diets. Twelve normal term babies with identical repletion levels of 25-hydroxyvitamin D (25D) were fed sequentially with starting formulas that differed only in their carbohydrate sources: lactose (control) and polycose. A 3-day test was performed after a 1-week adjustment to the new diet. Fecal excretion of calcium was significantly higher in the lactose-free formula period compared to the control one: 56.6 (13.9) versus 39.6 (12.8) mg/kg/day (p less than 0.02); subsequently, the net retention was considerably higher and statistically significant (p less than 0.01) for the control period versus the lactose-free formula period: 99.4 (15.3) versus 78.1 (14.3). Plasma 25D values were 21.8 (9.1) and 23.7 (7.1) ng/ml at the beginning of the lactose and polycose periods, respectively, and 1,25-dihydroxyvitamin-D values were 64 (62) and 75 (45) pg/ml, not significant. Results suggest that formulas containing polycose as the sole carbohydrate source may reduce the intestinal absorption of calcium in term newborns, but determining long-term biological significance requires further observation.

Calcium↗
PubMed1990

Purification and properties of two lactose hydrolases from Trichosporon cutaneum.

Two enzymes that hydrolysed lactose were purified essentially to homogeneity from cell extracts of the oleaginous yeast Trichosporon cutaneum. One enzyme of Mr 120,000 had properties typical of a beta-galactosidase (EC 3.2.1.23). It hydrolysed lactose, lactulose and nitrophenyl-beta-D-galactosides. The enzyme required K+ or Rb+ for activity, and other monovalent cations tested were not effective. Enzyme activity was abolished by EDTA and stimulated by Mg2+, Mn2+ and Ca2+. The beta-galactosidase was induced by lactose, galactose, lactulose and lactobionic acid. The other enzyme, a beta-glycosidase (EC 3.2.1.21) of Mr 52,000 showed no ionic requirements and it hydrolysed lactose, nitrophenyl-beta-D-galactosides, 4-nitrophenyl-beta-D-glucoside, cellobiose, laminaribiose, laminaritriose and sophorose, but not gentiobiose, 4-nitrophenyl-beta-D-mannoside or sucrose. This enzyme was induced by lactose, galactose and lactulose, and also by cellobiose.

Cations↗
PubMed1980

Ammonia production by intestinal bacteria: the effects of lactose, lactulose and glucose.

Ammonia production by eight groups of intestinal bacteria was measured, and the effect on ammonia production of lowered pH and ambient ammonia concentration was determined. Endogenous ammonia production from bacterial protoplasm was also examined. To examine the mechanisms by which fermentable substrates reduce ammonia formation in a faecal incubation system, the effect of lactose, lactulose or glucose on ammonia release by pure cultures of intestinal bacteria was studied. The largest amounts of ammonia were generated by gram-negative anaerobes, clostridia, enterobacteria, and Bacillus spp. Gram-positive non-sporing anaerobes, streptococci and micrococci formed modest amounts, and lactobacilli and yeasts formed very little ammonia. All groups of bacteria formed less ammonia at pH 5.0 than at pH 7.0 and production of ammonia was not inhibited when 30 mmol ammonia/litre was included in the medium. Small amounts of ammonia were formed due to endogenous metabolism of bacterial cells. Washed cell suspensions of four isolates of Bacteroides, one clostridial isolate and two streptococcal isolates formed less ammonia from alanine, methionine or histidine after growth in the presence of either lactose or lactulose. In contrast, the Bacteroides isolates formed more ammonia from aspartate than from either lactose or lactulose. Also, cultures of gram-negative anaerobes and enterobacteria, and to a lesser extent clostridia and streptococci, formed significantly less ammonia in nutrient broth when lactose, lactulose or glucose was included in the medium. This decrease in ammonia formation was not due to a fall in pH of the medium. Ammonia production by gram-positive non-sporing anaerobes was not affected by carbohydrate fermentation. These results suggest that gram-negative anaerobic bacteria make a major contribution to ammonia generated from peptides and amino acids in vivo, and that ammonia may be formed from bacterial cells in the colon. Fermentation of lactose and lactulose may repress the formation and inhibit the activity of enzymes responsible for ammonia release. In the human colon these substrate effects may decrease the amount of ammonia available to exert a toxic effect on the host, and thus contribute to the beneficial effects of lactulose when it is used in the treatment of portosystemic encephalopathy.

Amino Acids↗
PubMed1995

Effect of lactose, lactulose and bisacodyl on gastrointestinal transit studied by metal detector.

AIM AND METHODS: To study the effect of 45 g lactose, 30 g lactulose and 10 mg bisacodyl on gastrointestinal transit in 30 healthy volunteers by metal detector and Hinton marker method. The first set of measurements were performed under standard conditions. In a second stage, transit was slowed to twice the original value by loperamide to simulate constipation conditions. RESULTS: Bisacodyl drastically accelerated small and large intestinal transit. Colonic transit was shortened to 23% and to 31% of control values, without and with loperamide. Bisacodyl increased stool weight and decreased stool consistency in all persons. Lactulose marginally shortened small intestinal transit (P = 0.08) but significantly increased stool weight and decreased stool consistency. The accelerating effect of lactose on small intestinal transit was abolished by loperamide. Lactose did not influence colonic transit, stool weight or stool consistency. Results of metal detector and Hinton marker method corresponded well (r = 0.75), the metal detector method measuring slightly shorter transit times than the Hinton marker method. CONCLUSIONS: With the dose chosen in this trial, lactose did not have any laxative effect in lactose tolerant persons. Laxative effect was mild with lactulose and most pronounced with bisacodyl.

Adult↗
PubMed2005

Abnormal breath tests to lactose, fructose and sorbitol in irritable bowel syndrome may be explained by small intestinal bacterial overgrowth.

BACKGROUND: Small intestinal bacterial overgrowth and sugar malabsorption (lactose, fructose, sorbitol) may play a role in irritable bowel syndrome. The lactulose breath test is a reliable and non-invasive test for the diagnosis of small intestinal bacterial overgrowth. The lactose, fructose and sorbitol hydrogen breath tests are widely used to detect specific sugar malabsorption. AIM: To assess the extent to which small intestinal bacterial overgrowth may influence the results of hydrogen sugar breath tests in irritable bowel syndrome patients. METHODS: We enrolled 98 consecutive irritable bowel syndrome patients. All subjects underwent hydrogen lactulose, lactose, fructose and sorbitol hydrogen breath tests. Small intestinal bacterial overgrowth patients were treated with 1-week course of antibiotics. All tests were repeated 1 month after the end of therapy. RESULTS: A positive lactulose breath test was found in 64 of 98 (65%) subjects; these small intestinal bacterial overgrowth patients showed a significantly higher prevalence of positivity to the lactose breath test (P < 0.05), fructose breath test (P < 0.01) and sorbitol breath test (P < 0.01) when compared with the small intestinal bacterial overgrowth-negatives. Small intestinal bacterial overgrowth eradication, as confirmed by negative lactulose breath test, caused a significant reduction in lactose, fructose and sorbitol breath tests positivity (17% vs. 100%, 3% vs. 62%, and 10% vs. 71% respectively: P < 0.0001). CONCLUSIONS: In irritable bowel syndrome patients with small intestinal bacterial overgrowth, sugar breath tests may be falsely abnormal. Eradication of small intestinal bacterial overgrowth normalizes sugar breath tests in the majority of patients. Testing for small intestinal bacterial overgrowth should be performed before other sugar breath tests tests to avoid sugar malabsorption misdiagnosis.

Adult↗
PubMed1994

Kinetics of lactose-reversible coadhesion of Actinomyces naeslundii WVU 398A and Streptococcus oralis 34 on the surface of hexadecane droplets.

Most investigations of mechanisms accounting for intergeneric coaggregation have emphasized stereospecific rather than nonspecific interactions. The purpose of this investigation was to determine the relative importance of lectin-carbohydrate and nonspecific hydrophobic and ionic interactions, using a model based on strains with one of the most well understood specific coaggregation mechanisms, the lactose-reversible coaggregation of Actinomyces naeslundii and Streptococcus oralis. The kinetics of coadhesion and desorption of coadherent bacteria were studied using S. oralis 34 bound to hexadecane droplets as an affinity support for the adhesion of A. naeslundii WVU 398A. Light, confocal microscopy and transmission electron microscopy confirmed that A. naeslundii cells adhered only to the S. oralis cells, not to exposed hexadecane between the streptococci. Coadhesion was inhibited by lactose concentrations as low as 2.0 mM. The rate of coadhesion was halved at 60 mM lactose. The hydrophobicity inhibitors bovine serum albumin and defatted bovine serum albumin and the salts LiCl and KCl failed to inhibit coadhesion in the hexadecane assay, and bovine serum albumin also failed to inhibit coaggregation in a bacterial aggregation assay on glass slides. High concentrations of the salts achieved a 50% rate decrease in A. naeslundii adhesion to the S. oralis-coated droplets only when they were combined with > 20 mM lactose. Sodium dodecyl sulfate (SDS) and Tween 20 inhibition was tested by the slide coaggregation assay because they tended to emulsify the droplets; SDS was inhibitory. Lactose selectively desorbed A. naeslundii from S. oralis-coated droplets at low concentrations equivalent to those that inhibited coadhesion. Neither LiCl nor KCl desorbed A. naeslundii from the droplets, even at 500 mM. At low concentrations, SDS but not Tween 20 eluted both A. naeslundii and S. oralis from the droplets. Although the SDS results might suggest a degree of cooperative charge interactions, the results support the hypothesis that stereospecific, beta-galactoside-sensitive interactions have a much greater impact than nonspecific interactions on the coadhesion of A. naeslundii and S. oralis.

Actinomyces↗
PubMed1984

Molecular cloning of the lactose-metabolizing genes from Streptococcus lactis.

Restriction endonucleases and agarose gel electrophoresis were used to analyze plasmid pLM2001, which is required for lactose metabolism by Streptococcus lactis LM0232. The enzymes XhoI, SstI, BamHI, and KpnI each cleaved the plasmid into two fragments, whereas EcoRI and BglII cleaved the plasmid into seven and five fragments, respectively. Sizing of fragments and multiple digestions allowed construction of a composite restriction map. The KpnI fragments of pLM2001 were cloned into the KpnI cleavage site of the vector plasmid pDB101. A recombinant plasmid (pSH3) obtained from a lactose-fermenting, erythromycin-resistant (Lac+ Eryr) transformant of Streptococcus sanguis Challis was analyzed by enzyme digestion and agarose gel electrophoresis. Plasmid pSH3 contained 7 of the 11 KpnI-HindIII fragments from pLM2001 and 5 of the 7 fragments from pDB101. It was determined that a 23-kilobase (kb) KpnI-generated fragment from pLM2001 had been cloned into pDB101 with deletion of part of the vector plasmid. The recombinant plasmid could be transformed with high frequency into several Lac- strains of S. sanguis, conferring the ability to ferment lactose and erythromycin resistance. The presence of pSH3 allowed a strain deficient in Enzyme IIlac, Factor IIIlac, and phospho-beta-galactosidase of the lactose phosphoenolpyruvate-dependent phosphotransferase system to efficiently ferment lactose. Under conditions designed to maximize curing of plasmid DNA with acriflavin, no Lac- derivatives could be isolated from cells transformed with pSH3. Seven of the 40 Lac+ colonies isolated after 10 transfers in acriflavin were shown to be sensitive to erythromycin and did not appear to harbor plasmid DNA.(ABSTRACT TRUNCATED AT 250 WORDS)

Base Sequence↗
PubMed1995

Production of galacto-oligosaccharide from lactose by Sterigmatomyces elviae CBS8119.

Our stock cultures were screened for microorganisms that can produce galacto-oligosaccharide (Gal-OS) from lactose. Of the 574 strains of bacteria and yeasts tested, Sterigmatomyces elviae CBS8119, Rhodotorula minuta IFO879, and Sirobasidium magnum CBS6803 were found to be efficient producers of Gal-OS from lactose and S. elviae CBS8119 was selected as a representative, high-level producing strain. With toluene-treated resting S. elviae CBS8119 cells, 135 mg of Gal-OS per ml was produced from 360-mg/ml lactose. During this reaction, the by-product glucose was found to inhibit Gal-OS production. Therefore, in order to remove the glucose from the reaction mixture, a culture method in which cell growth followed the enzymatic reaction was devised, which increased the yield of Gal-OS considerably because of the consumption of glucose for cell growth. Under such conditions, 232 mg of Gal-OS per ml was produced from 360-mg/ml lactose after incubation at 30 degrees for 60 h. The structure of the major product was identified as O-beta-D-galactopyranosyl-(1-->4)-O-beta-D-galactopyranosyl-(1-->4)-D- glucopyranose (4'-galactosyl-lactose) by 13C nuclear magnetic resonance spectroscopy.

Bacteria↗
PubMed2000

Integrative food-grade expression system based on the lactose regulon of Lactobacillus casei.

The lactose operon from Lactobacillus casei is regulated by very tight glucose repression and substrate induction mechanisms, which made it a tempting candidate system for the expression of foreign genes or metabolic engineering. An integrative vector was constructed, allowing stable gene insertion in the chromosomal lactose operon of L. casei. This vector was based on the nonreplicative plasmid pRV300 and contained two DNA fragments corresponding to the 3' end of lacG and the complete lacF gene. Four unique restriction sites were created, as well as a ribosome binding site that would allow the cloning and expression of new genes between these two fragments. Then, integration of the cloned genes into the lactose operon of L. casei could be achieved via homologous recombination in a process that involved two selection steps, which yielded highly stable food-grade mutants. This procedure has been successfully used for the expression of the E. coli gusA gene and the L. lactis ilvBN genes in L. casei. Following the same expression pattern as that for the lactose genes, beta-glucuronidase activity and diacetyl production were repressed by glucose and induced by lactose. This integrative vector represents a useful tool for strain improvement in L. casei that could be applied to engineering fermentation processes or used for expression of genes for clinical and veterinary uses.

Escherichia coli↗
PubMed2001

Requirement for phosphoglucomutase in exopolysaccharide biosynthesis in glucose- and lactose-utilizing Streptococcus thermophilus.

To study the influence of phosphoglucomutase (PGM) activity on exopolysaccharide (EPS) synthesis in glucose- and lactose-growing Streptococcus thermophilus, a knockout PGM mutant and a strain with elevated PGM activity were constructed. The pgmA gene, encoding PGM in S. thermophilus LY03, was identified and cloned. The gene was functional in Escherichia coli and was shown to be expressed from its own promoter. The pgmA-deficient mutant was unable to grow on glucose, while the mutation did not affect growth on lactose. Overexpression of pgmA had no significant effect on EPS production in glucose-growing cells. Neither deletion nor overexpression of pgmA changed the growth or EPS production on lactose. Thus, the EPS precursors in lactose-utilizing S. thermophilus are most probably formed from the galactose moiety of lactose via the Leloir pathway, which circumvents the need for a functional PGM.

Galactose↗
PubMed2003

Unusual organization for lactose and galactose gene clusters in Lactobacillus helveticus.

The nucleotide sequences of the Lactobacillus helveticus lactose utilization genes were determined, and these genes were located and oriented relative to one another. The lacLM genes (encoding the beta-galactosidase protein) were in a divergent orientation compared to lacR (regulatory gene) and lacS (lactose transporter). Downstream from lacM was an open reading frame (galE) encoding a UDP-galactose 4 epimerase, and the open reading frame had the same orientation as lacM. The lacR gene was separated from the downstream lacS gene by 2.0 kb of DNA containing several open reading frames that were derived from fragmentation of another permease gene (lacS'). Northern blot analysis revealed that lacL, lacM, and galE made up an operon that was transcribed in the presence of lactose from an upstream lacL promoter. The inducible genes lacL and lacM were regulated at the transcriptional level by the LacR repressor. In the presence of glucose and galactose galE was transcribed from its promoter, suggesting that the corresponding enzyme can be expressed constitutively. Lactose transport was inducible by addition of lactose to the growth medium.

Amino Acid Sequence↗
PubMed2004

Heterologous expression of lactose- and galactose-utilizing pathways from lactic acid bacteria in Corynebacterium glutamicum for production of lysine in whey.

The genetic determinants for lactose utilization from Lactobacillus delbrueckii subsp. bulgaricus ATCC 11842 and galactose utilization from Lactococcus lactis subsp. cremoris MG 1363 were heterologously expressed in the lysine-overproducing strain Corynebacterium glutamicum ATCC 21253. The C. glutamicum strains expressing the lactose permease and beta-galactosidase genes of L. delbrueckii subsp. bulgaricus exhibited beta-galactosidase activity in excess of 1000 Miller units/ml of cells and were able to grow in medium in which lactose was the sole carbon source. Similarly, C. glutamicum strains containing the lactococcal aldose-1-epimerase, galactokinase, UDP-glucose-1-P-uridylyltransferase, and UDP-galactose-4-epimerase genes in association with the lactose permease and beta-galactosidase genes exhibited beta-galactosidase levels in excess of 730 Miller units/ml of cells and were able to grow in medium in which galactose was the sole carbon source. When grown in whey-based medium, the engineered C. glutamicum strain produced lysine at concentrations of up to 2 mg/ml, which represented a 10-fold increase over the results obtained with the lactose- and galactose-negative control, C. glutamicum 21253. Despite their increased catabolic flexibility, however, the modified corynebacteria exhibited slower growth rates and plasmid instability.

Bacterial Proteins↗
PubMed2005

Alternative lactose catabolic pathway in Lactococcus lactis IL1403.

In this study, we present a glimpse of the diversity of Lactococcus lactis subsp. lactis IL1403 beta-galactosidase phenotype-negative mutants isolated by negative selection on solid media containing cellobiose or lactose and X-Gal (5-bromo-4-chloro-3-indolyl-beta-d-galactopyranoside), and we identify several genes essential for lactose assimilation. Among these are ccpA (encoding catabolite control protein A), bglS (encoding phospho-beta-glucosidase), and several genes from the Leloir pathway gene cluster encoding proteins presumably essential for lactose metabolism. The functions of these genes were demonstrated by their disruption and testing of the growth of resultant mutants in lactose-containing media. By examining the ccpA and bglS mutants for phospho-beta-galactosidase activity, we showed that expression of bglS is not under strong control of CcpA. Moreover, this analysis revealed that although BglS is homologous to a putative phospho-beta-glucosidase, it also exhibits phospho-beta-galactosidase activity and is the major enzyme in L. lactis IL1403 involved in lactose hydrolysis.

Bacterial Proteins↗
PubMed1984

Exclusive presence of lactose-sensitive fimbriae on a typical strain (WVU45) of Actinomyces naeslundii.

Lactose-sensitive fimbriae were identified as the only fimbriae present on Actinomyces naeslundii WVU45 (ATCC 12104). A single antigen reactive with antiserum against WVU45 cells was detected by cross immunoelectrophoresis of isolated fimbriae, and a monospecific antiserum against this antigen reacted with all fimbriae observed on the bacterial surface by immunoelectron microscopy. Moreover, the loss of one cell surface antigen by a spontaneous mutant of A. naeslundii WVU45 (WVU45M), isolated by its failure to react with a monospecific antibody against the fimbriae, was associated with the loss of all fimbriae. The functional involvement of the fimbriae in lactose-sensitive bacterial adherence was demonstrated by the ability of WVU45, but not WVU45M, cells to agglutinate neuraminidase-treated erythrocytes and by the lactose-sensitive hemagglutinating activity of immune complexes formed with isolated fimbriae and monospecific antibody. Bacterial agglutination assays with different monospecific antibodies revealed an antigenic similarity between the fimbriae of A. naeslundii WVU45 and the lactose-sensitive fimbriae (type 2) of Actinomyces viscosus T14V. In contrast, cross-reactivity was not observed between the WVU45 fimbriae and type 1 fimbriae, the structures involved in lactose-resistant adherence of strain T14V to saliva-treated hydroxyapatite. Functional differences between the fimbriae of A. naeslundii and A. viscosus strains may be correlated with well-established differences in the in vivo distribution of these organisms: namely, the preference of typical A. naeslundii for epithelial surfaces and of A. viscosus for tooth surfaces.

Actinomyces↗
PubMed1974

Regulation of the synthesis of the lactose repressor.

Measurements of the lactose repressor over a tenfold range of cell growth rates were made on protein extracts from Escherichia coli cultures grown in media with various carbon energy sources. The concentration of lactose repressor varied with the number of genome equivalents per cell over this range in growth rates, suggesting that the number of lactose molecules within the cell is determined by the number of I gene copies present. The timing of repressor synthesis during the cell division cycle and its correlation with deoxyribonucleic acid synthesis was examined by synchronizing the cell division cycle of E. coli ED1039, in which the Lac region has been transposed from 10 to 36 min on the genetic map. Measurements of lactose repressor in the synchronized culture revealed a burst of repressor synthesis at the time of I gene duplication. The concentration of lactose repressor was found to decrease as a function of total cell protein during the division cycle until an increase in synthesis occurred, suggesting that repressor synthesis probably does not occur throughout the division cycle. A model for I gene regulation is proposed.

Ammonium Sulfate↗
PubMed1976

Expression and regulation of lactose genes carried by plasmids.

A number of plasmids carrying the lactose character have been studied. All of the plasmids examined so far code for proteins essential for lactose utilization, i.e., beta-galactosidase and galactoside permease. None of them carries enzymatically or immunologically detectable thiogalactoside transacetylase. The expression of the two enzymes is both negatively and positively controlled: they are inducible by different galactosides and are sensitive to catabolite repression. Since the plasmid-coded lactose systems have many features in common with the Escherichia coli lactose operon, it is suggested that the plasmids could have acquired the lactose genes from an E. coli chromosome.

Acetyltransferases↗
PubMed1978

Permease-specific mutations in Salmonella typhimurium and Escherichia coli that release the glycerol, maltose, melibiose, and lactose transport systems from regulation by the phosphoenolpyruvate:sugar phosphotransferase system.

Several carbohydrate permease systems in Salmonella typhimurium and Escherichia coli are sensitive to regulation by the phosphoenolpyruvate:sugar phosphotransferase system. Mutant Salmonella strains were isolated in which individual transport systems had been rendered insensitive to regulation by sugar substrates of the phosphotransferase system. In one such strain, glycerol uptake was insensitive to regulation; in another, the maltose transport system was resistant to inhibition; and in a third, the regulatory mutation specifically rendered the melibiose permease insensitive to regulation. An analogous mutation in E. coli abolished inhibition of the transport of beta-galactosides via the lactose permease system. The mutations were mapped near the genes which code for the affected transport proteins. The regulatory mutations rendered utilization of the particular carbohydrates resistant to inhibition and synthesis of the corresponding catabolic enzymes partially insensitive to repressive control by sugar substrates of the phosphotransferase system. Studies of repression of beta-galactosidase synthesis in E. coli were conducted with both lactose and isopropyl beta-thiogalactoside as exogenous sources of inducer. Employing high concentrations of isopropyl beta-thiogalactoside, repression of beta-galactosidase synthesis was not altered by the lactose-specific transport regulation-resistant mutation. By contrast, the more severe repression observed with lactose as the exogenous source of inducer was partially abolished by this regulatory mutation. The results support the conclusions that several transport systems, including the lactose permease system, are subject to allosteric regulation and that inhibition of inducer uptake is a primary cause of the repression of catabolic enzyme synthesis.

Biological Transport↗
PubMed1982

Transgalactosylation activity of ebg beta-galactosidase synthesizes allolactose from lactose.

ebg enzyme, the second beta-galactosidase of Escherichia coli, does not normally convert lactose into an inducer of the lac operon. We previously reported the existence of a mutant ebg enzyme that does make such an inducer in vivo (Rolseth et al., J. Bacteriol. 142:1036-1039, 1980). Here I report that the mutant enzyme makes inducer from lactose in vitro and that the inducer is allolactose. Allolactose is made from lactose by direct transgalactosylation at a rate that is 8 to 10% of the rate of lactose hydrolysis. Galactose is also transferred to glucose free in solution, but the resulting indirect transgalactosylation products are not allolactose or lactose. The ability to efficiently synthesize allolactose is a general property of class IV mutant ebg enzymes, whereas other classes of ebg mutant enzymes are unable to synthesize allolactose efficiently. The evolutionary implications of this new function are discussed.

Enzyme Induction↗