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PubMed1986

Lactose and melibiose metabolism in Erwinia chrysanthemi.

A Lac+ mutant of Erwinia chrysanthemi was isolated from the Lac- wild type on lactose agar. beta-Galactosidase was expressed independently of lactose transport in both the mutant and the wild type, and neither strain expressed thiogalactoside transacetylase. Lactose transport and alpha-galactosidase, constitutive in the Lac+ strain, were coordinately induced in the Lac- strain by melibiose and raffinose but not by isopropyl-beta-D-thiogalactopyranoside or thiomethyl-beta-D-galactopyranoside. Melibiose was a strong inhibitor of both the melibiose- and the raffinose-induced lactose permeases, whereas raffinose was a strong inhibitor of only the raffinose-induced lactose permease.

Acetyltransferases↗

PubMed1967

Glucose-lactose diauxie in Escherichia coli.

Growth of Escherichia coli in medium containing glucose, at a concentration insufficient to support full growth, and containing lactose, is diauxic. A mutation in the gene, CR, which determines catabolite repression specific to the lac operon, was found to relieve glucose-lactose but not glucose-maltose diauxie. Furthermore, a high concentration of lactose was shown to overcome diauxie in a CR(+) strain. Studies on the induction of beta-galactosidase by lactose suggested that glucose inhibits induction by 10(-2)m lactose. Preinduction of the lac operon was found to overcome this effect. The ability of glucose to prevent expression of the lac operon by reducing the internal concentration of inducer as well as by catabolite repression is discussed.

Enzyme Induction↗

PubMed1969

Mutant of Escherichia coli exhibiting a cold-sensitive phenotype for growth on lactose.

As part of a study on the effect of low temperature on cellular regulatory processes, a class of lactose-negative mutants of Escherichia coli K-12 was isolated which could use lactose as a sole carbon and energy source at 37 C, but which could not use this sugar at 20 C. The lactose operon of the mutants functioned normally at 20 C. Galactose exhibited a strong inhibitory effect on growth, especially at 20 C. Growth of the mutants on glycerol was stopped at 20 C and slowed considerably at 37 C if galactose was added to the medium. Making the mutants galactose-positive eliminated the cold sensitivity of lactose utilization. One mutant was shown to be galactose-1-phosphate uridyl transferase-negative, galactose-kinase heat-sensitive, and uridine diphosphate-galactose-4-epimerase-positive. It is postulated that the mutant is able to phosphorylate galactose at 20 C (if only at a very low rate), but lacking transferase it is poisoned by the accumulation of galactose-1-phosphate. At 37 C, galactokinase is nonfunctional and the mutant grows on the glucose moiety of lactose.

Enzyme Induction↗

PubMed1969

Involvement of phosphoenolpyruvate in lactose utilization by group N streptococci.

The effect of sodium fluoride on lactose metabolism and o-nitrophenyl-beta-d-galactopyranoside (ONPG) hydrolysis by Streptococcus lactis strains 7962 and C(2)F suggested that different mechanisms of lactose utilization existed in the two strains. Sodium fluoride prevented lactose utilization and ONPG hydrolysis by whole cells of S. lactis C(2)F but had no effect on S. lactis 7962. Although hydrolysis of ONPG by toluene-treated cells of S. lactis 7962 occurred without addition of phospho-enolpyruvate (PEP), toluene-treated cells of S. lactis C(2)F required the presence of this cofactor. Concentrated cell extracts of S. lactis C(2)F hydrolyzed ONPG; this hydrolysis was inhibited by NaF, but the addition of PEP, in the presence of NaF, restored maximal activity. Addition of acetyl-phosphate, carbamyl-phosphate, adenosine-5'-triphosphate, guanosine-5'-triphosphate, or uridine-5'-triphosphate did not stimulate activity. The presence of cofactors did not stimulate and NaF did not inhibit the hydrolysis in extracts of S. lactis 7962. To confirm the operation of two mechanisms, S. lactis 7962 was shown to hydrolyze lactose to glucose and galactose, whereas S. lactis C(2)F was unable to split the disaccharide. In addition, whole cells of S. lactis C(2)F rapidly accumulated a phosphorylated derivative of thiomethyl-beta-d-galactoside (TMG) which behaved chromatographically and electrophoretically like TMG-PO(4). Unexpectedly, S. lactis 7962 also accumulated a TMG derivative, although the rate was extremely low. These data indicate that different mechanisms of lactose utilization exist in the two strains, with a phosphorylation step dependent on PEP involved in S. lactis C(2)F.

Azides↗

PubMed2000

Diagnostic and public health dilemma of lactose-fermenting Salmonella enterica serotype Typhimurium in cattle in the Northeastern United States.

The presence of lactose-fermenting Salmonella strains in clinical case materials presented to microbiology laboratories presents problems in detection and identification. Failure to detect these strains also presents a public health problem. The laboratory methods used in detecting lactose-fermenting Salmonella enterica serotype Typhimurium from six outbreaks of salmonellosis in veal calves are described. Each outbreak was caused by a multiply-resistant and lactose-fermenting strain of S. enterica serotype Typhimurium. The use of Levine eosin-methylene blue agar in combination with screening of suspect colonies for C8 esterase enzyme and inoculation of colonies into sulfide-indole-motility medium for hydrogen sulfide production was particularly effective for their detection. A hypothesis for the creation of lactose-fermenting salmonellae in the environment is presented. It is proposed that the environment and husbandry practices of veal-raising barns provide a unique niche in which lactose-fermenting salmonellae may arise.

Animal Feed↗

PubMed1987

GAL4 of Saccharomyces cerevisiae activates the lactose-galactose regulon of Kluyveromyces lactis and creates a new phenotype: glucose repression of the regulon.

A Kluyveromyces lactis mutant defective in lac9 cannot induce beta-galactosidase or galactokinase activity and is unable to grow on lactose or galactose. When this strain was transformed with the GAL4 positive regulatory gene of Saccharomyces cerevisiae it was able to grow on lactose or galactose as the sole carbon source. Transformants bearing GAL4 exhibited a 4.5-h generation time on galactose or lactose, versus 24 h for the nontransformed lac9 strain. A K. lactis lac9 strain bearing two integrated copies of GAL4 showed 3.5-fold induction of beta-galactosidase activity and 1.8-fold induction of galactokinase activity compared with 15.6-fold and 4.4-fold induction, respectively, for the LAC9 wild-type strain. In transformants bearing 10 integrated copies of GAL4, the induced level of beta-galactosidase was nearly as high as in the LAC9 wild-type strain. In addition to restoring lactose and galactose gene expression, GAL4 in K. lactis lac9 mutant cells conferred a new phenotype, severe glucose repression of lactose and galactose-inducible enzymes. Glucose repressed beta-galactosidase activity 35- to 74-fold and galactokinase activity 14- to 31-fold in GAL4 transformants, compared with the 2-fold glucose repression exhibited in the LAC9 wild-type strain. The S. cerevisiae MEL1 gene was repressed fourfold by glucose in LAC9 cells. In contrast, the MEL1 gene in a GAL4 lac9 strain was repressed 20-fold by glucose. These results indicate that the GAL4 and LAC9 proteins activate transcription in a similar manner. However, either the LAC9 or GAL4 gene or a product of these genes responds differently to glucose in K. lactis.

Enzyme Induction↗

PubMed1975

The effect of glucose and lactose on beta-D-galactosidase activity and formation of sclerotia in Sclerotium rolfsii.

Addition of 0.5% (w/v) lactose to a glucose-mineral mdeium (SM) induced formation of sclerotia and beta-D-galactosidase (beta-D-galactoside galactohydrolase)(EC 3.2.1.23) synthesis in Sclerotium rolfsii types A and R; These effects as well as lactose uptake were inversely related to glucose concentration within the tested range of 0.5 to 2.5% (w/v). Transfer of lactose-grown colonies to a glucose-supplemented medium nullified the inducible effect of lactose on formation of sclerotia, whereas transfer to water agar did not. It is concluded that glucose nullifies the effect of lactose on S. rolfsii by interfering with its active uptake.

Galactosidases↗

PubMed1992

In vivo estimation of lactose hydrolysis in premature infants using a dual stable tracer technique.

To investigate their putative capacity for lactose digestion, primed continuous orogastric infusions of [1-13C]glucose and D-[1-13C]lactose were administered on consecutive days to five premature infants (30-31 wk gestation, 15-32 days of age), who were fed by orogastric infusions of human milk or formula. By monitoring the plateau isotopic enrichment of plasma glucose using isotopomers containing the entire derivatized glucose molecule or C-2 through C-6, we were able to distinguish label appearing in the peripheral circulation deriving from unmetabolized glucose from that arising from recycled or fermented glucose (or lactose). Isotopic enrichment of the C-1 of glucose, corrected for recycling, was then calculated during each tracer infusion, and the fraction of dietary lactose subjected to in vivo hydrolysis was estimated from these values and the respective tracer infusion rates, assuming similar absorptive and metabolic fates of labeled glucose arising from either tracer. This fraction averaged 1.02 +/- 0.16 (SD), suggesting that lactose digestion is efficient by 34-wk postconceptional age.

Bicarbonates↗

PubMed2004

Validation of lactose[15N,15N]ureide as a tool to study colonic nitrogen metabolism.

In vitro experiments have shown that fermentation of carbohydrates prevents accumulation of nitrogen in the colon. Variable results have been obtained on modulation of dietary intakes in vivo. Lactose[15N,15N]-labeled ureide has been proposed as a tool to study colonic nitrogen metabolism. However, on oral administration of the marker, different urinary excretion patterns of the 15N label have been found. In this study, 50 mg lactose[15N,15N]ureide was directly instilled in the colon through an orocecal tube to investigate the colonic handling of this molecule in a direct way. In basal conditions, 42% (range, 37-48%) of labeled nitrogen administered as lactose[15N,15N]ureide was retrieved in urine after 72 h. A substantial variability in total urinary excretion of the label was found, but the urinary excretion pattern of the label was similar in all volunteers. When inulin, a fermentable carbohydrate, was administered together with the labeled marker, a significant decrease in urinary excretion of 15N after 72 h was found, to 29% (range, 23-34%). The effect of a smaller dose of inulin (250 mg) on colonic handling of lactose[15N,15N]ureide (50 mg), was investigated in another group of volunteers, and this time, fecal excretion of the marker was also evaluated. The results seem to indicate that fermentation of inulin causes an increased fecal excretion of the marker, thereby reducing urinary excretion but not retention in the human nitrogen pool. This instillation study shows that lactose[15N,15N]ureide is a tool with good properties to investigate the effect of different types of carbohydrates on nitrogen metabolism in the proximal colon in vivo.

Adult↗

PubMed1999

Ontogeny of intestinal safety factors: lactase capacities and lactose loads.

We measured intestinal safety factors (ratio of a physiological capacity to the load on it) for lactose digestion in developing rat pups. Specifically, we assessed the quantitative relationships between lactose load and the series capacities of lactase and the Na+-glucose cotransporter (SGLT-1). Both capacities increased significantly with age in suckling pups as a result of increasing intestinal mass and maintenance of mass-specific activities. The youngest pups examined (5 days) had surprisingly high safety factors of 8-13 for both lactase and SGLT-1, possibly because milk contains lactase substrates other than lactose; it also, however, suggests that their intestinal capacities were being prepared to meet future demands rather than just current ones. By day 10 (and also at day 15), increased lactose loads resulted in lower safety factors of 4-6, values more typical of adult intestines. The safety factor of SGLT-1 in day 30 (weanling) and day 100 (adult) rats was only approximately 1.0. This was initially unexpected, because most adult intestines maintain a modest reserve capacity beyond nutrient load values, but postweaning rats appear to use hindgut fermentation, assessed by gut morphology and hydrogen production assays, as a built-in reserve capacity. The series capacities of lactase and SGLT-1 varied in concert with each other over ontogeny and as lactose load was manipulated by experimental variation in litter size.

Aging↗

PubMed1985

Small intestine transit time and lactose absorption during phototherapy.

Diarrhea is often seen during phototherapy in jaundiced infants. Lactose malabsorption and reduced gut transit time (GTT) are some of the proposed explanations. However, the etiology of the diarrhea is still controversial. We investigated GTT and lactose absorption during phototherapy using the H2 breath test. Breath H2 was measured every 10 min for 150 min after feeding of jaundiced infants with and without phototherapy, and in controls. There were 12 newborns in each group. The time of increase of H2 excretion over 10 ppm was taken as the transit time. Lactose malabsorption was estimated by integrating the area under the excess H2 curve. No difference was found in GTT, lactose absorption, peak breath H2 and the time of the peak between phototherapy-treated infants and jaundiced and nonjaundiced infants. The results did not support the presence of lactose malabsorption during phototherapy and the decreased total GTT reported in the literature was not due to shortened small intestinal transit time.

Breath Tests↗

PubMed2004

Evaluation of a new coprocessed compound based on lactose and maize starch for tablet formulation.

The development of new direct compression excipients should include a comprehensive and rapid determination of deformation properties. The aim of this study was to characterize StarLac, a new coprocessed compound for direct compression based on lactose and maize starch. For this purpose, the effects of the base materials (maize starch and spray-dried lactose) were considered and the influence of the spray-drying process was investigated. This was performed by comparing the physical mixture of starch and spray-dried lactose at the same ratio as for StarLac. For analysis of the deformation behavior, the 3-D model and the Walker equation were applied; for verification, the Heckel equation and the pressure time function (a modified Weibull equation) were used. The advantages of StarLac are its good flowability depending on the spray-drying process, an acceptable crushing force due to its lactose content, its rapid disintegration depending on starch, and a brilliant fast release of an active ingredient, such as theophylline monohydrate. The volume-pressure deformation properties of StarLac were dependent on the lactose properties. Only at high maximum relative density (rho(rel, max)) did the influence of starch cause a change in these properties. A network-like structure can be observed using scanning electron microscopy pictures. Overall, StarLac deformed plastically with a low portion of elasticity. The physical mixture exhibited a more elastic behavior than StarLac. However, the part of the powder that was irreversibly compressed was much lower than was observed for the single substances. This behavior is caused by an interaction between the components, which in StarLac is prevented by spray drying.

Compressive Strength↗

PubMed2004

The surface roughness of lactose particles can be modulated by wet-smoothing using a high-shear mixer.

The surface morphology of a-lactose monohydrate particles was modified by a new wet-smoothing process performed in a high-shear mixer using solvents. Successive steps of wetting and drying of lactose powders during rolling in the mixer's cylindrical bowl were performed. Smoothed particles were tested for size distribution, flow, and packing. The wet-smoothing process flattened the surface and rounded the edges of lactose particles. In comparison with original lactose, an improvement of powder packing and flow properties was evidenced. When the process was performed in the presence of a ternary agent such as magnesium stearate, the smoothing was improved. The evolution of rugosity during the smoothing process was assessed through a fractal descriptor of SEM picture. Atomic force microscopy and surface area measurements quantified the surface rugosity. A very significant reduction of the rugosity, more remarkable in the presence of magnesium stearate, was measured. This new process of powder wet-smoothing allows the preparation of lactose particles with different degrees of smoothed surface for the control of flow and packing properties and particle-particle interactions.

Lactose↗

PubMed2005

Direct pelletization in a rotary processor controlled by torque measurements. III. Investigation of microcrystalline cellulose and lactose grade.

The aim of the present study was to investigate the use of different grades of microcrystalline cellulose (MCC) and lactose in a direct pelletization process in a rotary processor. For this purpose, a mixed 2- and 3-level factorial study was performed to determine the influence of the particle size of microcrystalline cellulose (MCC) (approximately 60 and 105 microm) and lactose (approximately 30, 40, and 55 microm), as well as MCC type (Avicel and Emcocel) on the pelletization process and the physical properties of the prepared pellets. A 1:4 mixture of MCC and lactose was applied, and granulation liquid was added until a 0.45 Nm increase in the torque of the friction plate was reached. All combinations of the 3 factors resulted in spherical pellets of a high physical strength. The particle size of MCC was found to have no marked effect on the amount of water required for agglomerate growth or on the size of the resulting pellets. An increasing particle size of lactose gave rise to more spherical pellets of a more narrow size distribution as well as higher yields. The MCC type was found to affect both the release of the model drug from the prepared pellets and the size distribution. Generally, the determined influence of the investigated factors was small, and direct pelletization in a rotary processor was found to be a robust process, insensitive to variations in the particle size and type of MCC and the particle size of lactose.

Cellulose↗

PubMed2000

Quantification of the surface morphologies of lactose carriers and their effect on the in vitro deposition of salbutamol sulphate.

Application of the scanning probe microscopy technique for quantitative measurement of the surface roughness of lactose carriers was evaluated. The roughness values of four different lactose carriers were related to the in vitro deposition results of the drug, salbutamol sulphate. The rugosity values of the lactose carriers were represented by Ra values which were in the order of DCL-40>DCL-11>lactose 325M>lactose 200 M. In vitro deposition results using a twin impinger showed that rougher carrier surfaces generally allowed more drug particles to be emitted from the capsules and inhaler but the availability of the drug to stage 2 was reduced, as detachment of drug particles from the carrier surfaces was more hindered. There was an optimum Ra value for greater delivery of the drug particles to stage 2 of the twin impinger. A balance between adherence and detachment of the drug from the carrier surface was needed in order to optimize the delivery of a drug to the desired target sites using a dry powder inhaler.

Adrenergic beta-Agonists↗

PubMed2000

Temperature-induced crystallization and compactibility of spray dried composite particles composed of amorphous lactose and various types of water-soluble polymer.

The purpose of this study was to investigate the temperature-induced crystallization and the compactibility of the composite particles containing amorphous lactose and various types of polymers. The composite particles were prepared by spray-drying an aqueous solution of lactose and various types of gel forming water-soluble polymers at various formulating ratios. The stabilizing effect of hydroxypropylcellulose (HPC) and polyvinyl pyrrolidone (PVP) on amorphous lactose in the composite particles was smaller than that of sodium alginate in comparing at the same formulating ratios. The difference in the stability of amorphous lactose in the composite particles was attributed to the difference in the glass transition temperature (Tg) of the composite particles caused by the polymers formulated. The tensile strength of compacted spray-dried composite particles containing the polymers was higher than commercial lactose for direct tabletting (DCL21). The tensile strength of the composite particles was increased with an increase in water content in the particles. The difference in compactibility of the composite particles containing the different amount of polymer and water could be explained by the difference in Tg of the particles.

Alginates↗

PubMed2003

Preparation of dry powder inhalation by surface treatment of lactose carrier particles.

An attempt was made to produce carrier particles for dry powder inhalations by the surface treatment of lactose particles with aqueous ethanol solution. Drug/carrier powder mixtures were prepared consisting of lactose carriers with different particle surface properties and micronized salbutamol sulfate. These powder mixtures were aerosolized by Spinhaler, and in vitro deposition properties of salbutamol sulfate were evaluated by twin impinger. The degree of adhesion between drug particles and carrier particles was determined by the ultracentrifuge separation method. In addition, the air jet sieve method was used to evaluate characteristics of the separation of drug particles from carrier particles in airflow. The average adhesion force (F50) between the surface-treated lactose carrier and drug particles was significantly lower than that of powder mixed with the untreated lactose carrier, indicating that the degree of separation (T50) of drug particles from carrier particles was improved when surface-treated lactose carrier was used. This resulted in an improvement of in vitro inhalation properties.

Drug Carriers↗

PubMed2004

Effect of surface layering time of lactose carrier particles on dry powder inhalation properties of salbutamol sulfate.

The effect of the surface layering time of lactose carrier particles on the dry powder inhalation properties of salbutamol sulfate was investigated. Lactose carrier particles were layered with vegetable magnesium stearate by physical mixing. In the present study, drug/carrier powder mixtures were designed consisting of micronized salbutamol sulfate and lactose carriers with various particle surface conditions prepared by surface layering. These powder mixtures were aerosolized by a Jethaler, and the in vitro deposition properties of salbutamol sulfate were evaluated by a twin impinger. Compared with the powder mixed with unlayered lactose carrier, the in vitro inhalation properties of the powder mixture prepared using the surface layering lactose carrier were significantly different, showing that the in vitro inhalation properties of the drug/carrier powder mixtures were improved. In vitro deposition properties (RP) increased with surface layering time. Using this surface layering system would thus be valuable for increasing the inhalation properties of dry powder inhalation.

Administration, Inhalation↗