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PubMed1983

Photoaffinity labeling of lactose synthase with a UDP-galactose analogue.

A photoaffinity analogue of UDP-galactose, 4-azido-2-nitrophenyluridylyl pyrophosphate (ANUP), has been synthesized for the investigation of the binding topography of alpha-lactalbumin on galactosyltransferase. Results obtained from steady state kinetics show that ANUP is an effective competitive inhibitor against UDP-galactose in the reactions of lactose and N-acetyllactosamine syntheses. The specific binding of ANUP to the UDP-galactose-binding site is further demonstrated by its ability to facilitate the formation of the lactose synthase complex on solid supports, either alone or in the presence of glucose or N-acetyl-glucosamine. ANUP inactivates galactosyltransferase on irradiation. One mole of ANUP was incorporated per mol of enzyme inactivated. This process is Mn2+-dependent and can be prevented by UDP-galactose. Glucose and N-acetylglucosamine render only partial protection. Photoaffinity labeling of lactose synthase either free in solution or immobilized on Sepharose does not result in any reduction of the alpha-lactalbumin modifier activity. In addition, no incorporation of radioactivity into alpha-lactalbumin was observed when radioactive ANUP was used, whereas galactosyltransferase was labeled. These data indicate that alpha-lactalbumin does not bind to galactosyltransferase in the region of the ANUP site, suggesting that the location of protein-protein interaction between the two subunits of lactose synthase may be removed from the UDP-galactose-binding domain.

Affinity Labels↗
PubMedDate not supplied

Enzymatic-ultraviolet method for measuring lactose in milk: collaborative study.

Collaborators in 8 dairy and food industry laboratories performed one lactose determination on each of 8 unknown samples of milk, lowfat milk, or skim milk, as 3 pairs of blind duplicates. Two known samples were provided to gain experience prior to analysis of the unknown samples. All of the above samples were also analyzed for lactose content by the official AOAC gravimetric method (16.507) by a commercial laboratory. From the overall mean of results on all samples, determinations by the enzymatic method averaged 0.49% lower than by the AOAC method. This difference was significant by the t-test (P = 0.05), which indicated a lack of agreement between the compared methods in determining lactose content. Standard deviations were similar for the 3 sets of blind duplicates which ranged between 3.67 and 4.55% lactose content. F-values revealed that variations between means obtained by laboratories differed significantly as compared with variations within laboratory means. The method has been adopted official first action.

Animals↗
PubMed1980

The clinical significance of lactose intolerance.

Lactose intolerance may give rise to a variety of gastro enterological symptoms depending on the degree of lactase deficiency present. A percentage of patients may be asymtomatic, but the presence of lactose in their diet leads to inadequate absorption of a variety of important nutrients resulting in deficiency disorders or less than optimal weight gain. The increase in migration from southern Europe and of late from Indo-China significantly increases the Australian population likely to be lactase-deficient. Many immigrants keen to adapt to the Australian way of life see milk as a new essential part of their diet. This, accompanied with a lack of basic English as a language, may compound the problem of diagnosis in these patients particularly if the medical practitioner is unaware of the syndrome. The ready availability of lactose-hydrolyzed milk powder as a Pharmaceutical Benefit should allow all patients to gain the nutritional advantage of milk without suffering the complications associated with lactose intolerance.

Adult↗
PubMedDate not supplied

Effect of Eimeria tenella infection on resistance to Salmonella typhimurium colonization in broiler chicks inoculated with anaerobic cecal flora and fed dietary lactose.

This study evaluated the effect of Eimeria tenella infection on Salmonella typhimurium colonization of broiler chicks following oral inoculation with anaerobic cecal flora either alone or with a treatment of 10% dietary lactose. The number of chicks colonized by S. typhimurium was significantly lower (P < 0.05) in groups inoculated with cecal flora with or without the dietary lactose treatment than in control groups. In addition, significantly fewer S. typhimurium organisms were isolated from the cecal contents of chicks inoculated with anaerobic cecal flora and treated with 10% dietary lactose than in the control chicks. Infection with E. tenella had no effect on the resistance of treated groups to S. typhimurium colonization of the ceca but did cause higher S. typhimurium colonization in the untreated control chicks. The results indicated that: A) anaerobic cecal flora given orally on the day of hatch to chicks with or without dietary lactose enhanced the resistance of the birds to Salmonella cecal colonization; and B) coccidial infection had no detrimental effect on this resistance to Salmonella colonization.

Animals↗
PubMed1994

[Experience regarding the use of arginine-lysine-lactose treatment in menopausal osteoporosis].

Two matched groups of postmenopausal patients were treated respectively with calcitonin or calcitonin and an arginine-lysine-glycerophosphoric acid-lactose association. The rationale underlying this therapy took the form of data in the literature which indicated an action of these amino acids and lactose on calcium absorption and on the metabolism of protein components in the skeletal structure. The following tests were performed: mineralometric evaluation, evaluation of painful symptoms and intake of pain-relieving drugs, serum levels of calcium, phosphorus, alkaline phosphatase, osteocalcin, parathormone, and calciuria and hydroxyproline. These parameters were assayed at the beginning and end of treatment which lasted six months. The results, or in other words the comparison between the two groups, basal or after treatment, and the values recorded before and after treatment in each group, enable the authors to affirm that the administration of the arginine-lysine-glycerophosphoric acid-lactose association leads to an increase in bone density and plasma osteocalcin, a reduction in painful symptoms and analgesic intake, and a reduction in the serum levels of parathromone and hydroxyproline. Data reported in the literature support the conclusion that the results obtained are the consequence of an improved intestinal absorption calcium. It is highly probable that the protein components of the association administered, arginine-lysine-glycerophosphoric acid-lactose, also exercise a direct action on osteoblasts and on the metabolism of bone matrix protein components.

Adult↗
PubMedDate not supplied

Nursing caries and lactose intolerance.

Caries is associated with fermentable carbohydrates in the diet. Dietary content can be related to personal and cultural preferences, availability of food, or physiologic tolerances. Twenty-seven percent of black children ages 12 to 24 months, in the Baltimore area were reported with symptoms of lactose intolerance. The incidence of lactose intolerance increased to 33 percent by age six years. At the same time, clinical observations of this same population suggested a high prevalence of nursing caries. One purpose of this study was to determine whether parents of black children with nursing caries perceived in their children more severe symptoms of lactose intolerance, which they related to milk products, than did parents of caries-free black children. A second purpose was to determine whether there were differences in feeding habits and types of fluids given children with nursing caries compared with caries-free children. A questionnaire concerning symptoms consistent with lactose intolerance, feeding habits, and fluid-selection was administered to the following groups: parents of 30 black children, ages 18 to 54 months, who were caries-free and parents of 30 black children, ages 18 to 54 months, diagnosed with nursing caries. Chi-square analysis or t-test analysis were performed on results accepting p < 0.05 as significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Age Factors↗
PubMed1993

[Lactose intolerance in the differential diagnosis of abdominal pain in children].

In the period from 1990 to 1992 542 children aged 0-15 years were examined by the breath hydrogen test for abdominal pain and chronic nutritional disorder. The results of lactose tests were pathological in 107 children with abdominal pain and 95 with chronic nutritional disorder. The authors followed 107 children with abdominal pain and directed their attention to its relationship to lactose intolerance. It was confirmed to be the only cause of abdominal pain in twenty-six children (24.3%). In spite of the well known pathogenetic mechanism of lactose intolerance leading to abdominal pain and metheorism and loose stools, an atypical clinical course was observed in these patients. There were no complaints associated with the intake of milk in history, the abdominal pain being the leading symptom in all patients but four who had loose stools. There was an improvement of clinical symptoms after the low-lactose diet.

Abdominal Pain↗
PubMedDate not supplied

Effect of mixed cecal microflora maintained in continuous culture and of dietary lactose on Salmonella typhimurium colonization in broiler chicks.

Mixed cecal microflora obtained from a mature chicken were maintained in vitro in continuous-flow (CF) culture. The effect of the CF culture and dietary lactose on Salmonella typhimurium cecal colonization in broiler chicks was evaluated. When averaged across four replicates, chicks treated with the culture alone (1.75 log10 decrease) or with 5% dietary lactose alone (2.98 log10 decrease) were protected against S. typhimurium. Optimum protection against S. typhimurium was observed when birds were treated with the culture in combination with dietary lactose (4.27 log10 decrease). Dietary lactose resulted in reduced cecal pH. A large increase in cecal propionic acid was observed in the birds given the CF culture. A significant correlation (P < 0.001) was observed between the cecal concentration of undissociated propionic acid and protection against S. typhimurium colonization (r = -0.78). The results indicated that indigenous cecal flora that protect against Salmonella colonization can be maintained without loss of efficacy in CF culture.

Animals↗
PubMedDate not supplied

Determination of fat, protein, and lactose in raw milk by Fourier transform infrared spectroscopy and by analysis with a conventional filter-based milk analyzer.

The accuracy of fat, crude protein (CP), true protein (TP), and lactose determinations of raw milk by Fourier transform infrared (FTIR) spectroscopy and by analysis with a conventional filter-based milk analyzer was assessed in 6 trials performed over a 10-month period. At each trial, 30 bulk milk samples collected from 15 European countries and 11 reconstituted milks made from raw milk components were analyzed. When calibrations were performed with reconstituted milks at each trial, accuracy standard deviations for fat, CP, TP, and lactose were, respectively, 0.050, 0.048, 0.035, and 0.076 g/100 g for the filter instrument and 0.047, 0.046, 0.042, and 0.065 g/100 g for the FTIR instrument. When a single calibration was made instead of calibrations at each trial, accuracy standard deviations increased for the filter instrument to 0.130, 0.119, 0.121, and 0.083 for fat, CP, TP, and lactose, respectively, and for the FTIR instrument to 0.082, 0.053, 0.044, and 0.084 g/100 g. Because the FTIR instrument provides more spectral information related to milk composition than does the filter instrument, single-calibration FTIR analysis of milk samples collected in different seasons is more accurate. Using reconstituted milks, prepared such that there is no correlation between fat, CP, and lactose, provides a more robust calibration than using genuine bulk milk, especially when milks with unusual composition are analyzed.

Animals↗
PubMed1996

[Poor digestion of lactose. Its definition, prevalence in Mexico, and its implications in milk consumption].

We review the studies that have been carried out in Mexico related to prevalence of lactase deficiency. We also describe a study carried out in three regions of Mexico with different consumption of milk (Northern, Central & Southeastern), comprising 960 individuals of ages ranging from 1 to 99 years. They were evaluated in a double blind study in order to determine the prevalence of lactose maldigestion with habitual dosis of milk. Each subject received two treatments: a) 240 or 360 mL of intact milk according to age, and b) the same amount of milk but with the lactose hydrolyzed (> 90% hydrolyzed). The participants were classified as digesters or maldigesters of lactose using the hydrogen breath test. The prevalence of maldigesters was higher in the Central (30%) and Southeastern (22%) regions than in the Northern one (9%, p < 0.01). The prevalence increased with age from 4.5% (< 3 years), 13.6% (3 to 5.9), 20.8% (6 to 12.9), 21.8% (13 to 17.9) and 32.9% in adults. Lactose maldigestion affected consumption marginally.

Adolescent↗
PubMed1996

[Lactose intolerance. Its definition, its prevalence in Mexico, and its implications in milk consumption].

In this document we describe some aspects of lactose and milk intolerance, discuss the results of studies carried out previously in Mexico, and report an investigation whose objective was to quantify the impact of lactose intolerance on the habitual consumption of milk in an open population. The prevalence of lactose intolerance and its effect on the consumption of milk was studied in three regions of Mexico. The design of the study was prospective, randomized, double-blind and crossover. The presence of milk intolerance was investigated in 960 subjects with ages between 6 months and 99 years who, as a function of age, received 240 or 360 mL of intact milk and the same amount of hydrolyzed milk. We quantified the consumption of milk and the presence of symptoms after ingesting the tested milk. Seven percent manifested symptoms with the intact milk but only 2% with the hydrolyzed milk (p < 0.001). The presence of symptoms in the intolerant subjects was significantly associated with a lower consumption of milk in comparison with the tolerant individuals (p < 0.001). On the other hand, the consumption of milk appeared to be only marginally associated with the intolerance and its symptoms. We conclude that lactose intolerance does not appear to be a major factor in determining milk consumption in Mexican healthy populations.

Adolescent↗
PubMed1979

Effect of an episode of severe malnutrition and age on lactose absorption by recovered infants and children.

The degree of which the ability to absorb lactose can be regained after recovery from an acute episode of severe malnutrition is in doubt. Lactase activity was indirectly assessed by means of a standard lactose tolerance test (2 g lactose per kilogram of body weight) in 71 Peruvian Mestizo infants and children (age 5 to 55 months) who had suffered such an episode. All were studied just before discharge after several months of hospital rehabilitation, during which linear growth and weight gain had accelerated and signs of significant malabsorption of other nutrients had disappeared. Only 39% of the total group had a positive test (delta blood glucose greater than 25 mg/dl); there was a decreasing proportion of positive responders with increasing age. No difference in response attributable to type or severity of malnutrition was found. Comparison of the present data with previous data from children in the same community who had never been acutely malnourished suggests that acute malnutrition may hasten the permanent decline of lactase activity normally expected later in life.

Acute Disease↗
PubMed2003

Assessment of hypolactasia and site-specific intestinal permeability by differential sugar absorption of raffinose, lactose, sucrose and mannitol.

The sugar absorption test is a non-invasive test for investigating intestinal permeability by simultaneous measurement of four probe sugars. In this study, we evaluated the utility of raffinose, lactose, sucrose and mannitol as probe sugars and calculated their urinary recovery as a percentage of ingested dose (mol/mol) and the recovery ratios of raffinose/mannitol, lactose/ raffinose and sucrose/raffinose. The reference ranges for these ratios, established from 39 healthy volunteers, are 0.005-0.015, 0.13-0.63 and 0.09-0.47, respectively. This sugar absorption test was performed in three patient groups. i) In 109 patients with aspecific gastrointestinal symptoms of whom intestinal histology was studied by duodenal biopsies: the urinary raffinose/mannitol recovery ratio highly correlated with gradation of duodenal damage; the sensitivity and specificity of the raffinose/mannitol ratio for detection of intestinal damage were 93% and 91%, respectively, using a cut-off level of 0.020. ii) In 70 patients in whom intestinal lactase activity was investigated by the lactose tolerance test: the urinary lactose/raffinose recovery ratio provided high diagnostic accuracy for hypolactasia (sensitivity 81% and specificity 89% at a cut-off level of 0.70). In analogy with the lactose/raffinose ratio, we suppose that the sucrose/raffinose ratio can be used as a marker of hyposucrasia. iii) In 40 patients with localized small intestinal damage, Crohn's disease of the ileum (n = 21) and celiac disease with histologically proven duodenal damage (n = 19): the raffinose/mannitol recovery ratio was increased in 100% of patients with celiac disease and in 81% of patients with Crohn's disease; increased lactose/raffinose recovery ratio (hypolactasia) and increased sucrose/raffinose (hyposucrasia) were present in 89% and 95% of celiac patients and 19% and 0% of Crohn's disease patients, respectively. The combination of the raffinose/mannitol ratio and sucrose/raffinose ratio appears to be an indication of the distribution of intestinal damage.

Administration, Oral↗
PubMed1996

Chemostat selection of an Escherichia coli mutant containing permease with enhanced lactose affinity.

Chemostats supplied with limited lactose were used to ask whether it was possible to generate and isolate any mutant of Escherichia coli lactose permease which allowed cells to grow faster. The permease and beta-galactosidase activities of the chemostat culture initially rose together to reach a plateau. After 30 days, the former underwent a second increase alone. From this culture, a faster-growing mutant was isolated. Its permease gene was cloned, sequenced, and found to have a single base pair changed. Thymine at position 199 was changed to guanine, resulting in serine 67 being substituted by alanine. Cells bearing this mutant in the plasmid could grow faster than parents in 10 microM lactose. The Km of the mutant permease toward lactose was 1.4 mM, about half of the wild-type value. Thus, a mutant with higher affinity for substrate could be selected from the chemostat.

Bacteriological Techniques↗
PubMed1986

Oral intake of glucose plus galactose and erythrocyte galactose-1-phosphate. A nutritional evaluation of hydrolyzed lactose.

This study deals with the metabolic effects of hydrolyzed lactose: After an overnight fast 5 healthy adult volunteers consumed a glucose-galactose mixture equivalent to 61.4 g of lactose (or 125 g of a dried skim milk powder with hydrolyzed lactose). The postprandial rise of erythrocyte galactose-1-phosphate (gal-1-P) never exceeded 22.3 mumol per liter packed red blood cells. This amounts to no more than 22% of the levels known from galactosemic children to be safe, concerning ocular, neural or hepatic damage. We conclude that the consumption of the hydrolyzed lactose does not cause a risk for consumer's health as judged from this galactose metabolite. A considerably higher risk, however, may accompany the consumption of galactose alone which causes around 17-fold higher plasma galactose levels and around 8-fold higher erythrocyte gal-1-P concentrations for more extended time periods.

Adult↗
PubMed2007

The lactose repressor system: paradigms for regulation, allosteric behavior and protein folding.

In 1961, Jacob and Monod proposed the operon model for gene regulation based on metabolism of lactose in Escherichia coli. This proposal was followed by an explication of allosteric behavior by Monod and colleagues. The operon model rationally depicted how genetic mechanisms can control metabolic events in response to environmental stimuli via coordinated transcription of a set of genes with related function (e.g. metabolism of lactose). The allosteric response found in the lactose repressor and many other proteins has been extended to a variety of cellular signaling pathways in all organisms. These two models have shaped our view of modern molecular biology and captivated the attention of a surprisingly broad range of scientists. More recently, the lactose repressor monomer was used as a model system for experimental and theoretical explorations of protein folding mechanisms. Thus, the lac system continues to advance our molecular understanding of genetic control and the relationship between sequence, structure and function.

Allosteric Regulation↗
PubMed1983

The roles of lactose and Clostridium difficile in the pathogenesis of enteral feeding associated diarrhoea.

This study investigated the influence of the disaccharide lactose on the incidence of clinically significant enteral feeding associated diarrhoea. In this double blind study both groups each of 25 patients were randomised to receive either a lactose containing diet Clinifeed 400 in 25 patients or a lactose free diet Ensure in 25 patients. Diarrhoea occurred with equal frequency in both treatment groups, even in those patients with symptomatic and biochemical evidence of impaired lactose handling. Although the onset of diarrhoea was significantly associated with antibiotic administration (p<0.01), Cl. difficile was not isolated from the stools of any patient with diarrhoea.

Journal Article↗