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PubMed1981

High performance liquid chromatographic determination of lactose in milk.

A rapid and simple high performance liquid chromatographic method for the determination of lactose in milk was developed. Samples were diluted with 0.5% perchloric acid and centrifuged, and an aliquot of the supernate was mixed with acetonitrile. Lactose was separated on a 10 micron particle-size silica column with aqueous acetonitrile as the mobile phase. The recovery of lactose from whole, skim, and chocolate milk averaged 99.2, 101.1, and 100.4%, respectively. Coefficients of variation for routinely performed duplicate determinations are between 1.0 and 1.5%.

Animals↗
PubMed1978

Ultrastructural changes in lactating guinea pig mammary gland slices associated with theophylline inhibition of lactose synthesis.

Mammary gland slices from lactating guinea pigs were incubated for periods up to 1 h in 10(-2) M theophylline which completely inhibits lactose synthesis. Ultrastructural comparison with control slices shows a significant increase in the size of the Golgi field involving an apparent back-up of microvesicles. Normally distended Golgi cisternae are flattened and contain fewer, less dense, protein granules. Theophylline decreases by 50% both types of secretory vacuoles present: a compact, 300 nm vacuole containing one 250 nm granule, and a swollen, approximately 700 nm vacuole with one or more granules. Changes in granule shape, density and formation were also observed. The findings suggest that the site where theophylline ingibits lactose synthesis may be in the translocation of substances, from the rough endoplasmic reticulum to the Golgi complex, e.g. the specifier protein alpha-lactalbumin which is essential to the lactose synthetase complex. The significance to the role of cyclic nucleotides in lactation is discussed.

Animals↗
PubMedDate not supplied

[Glycoprotein hexoses in feces of infants with lactose intolerance].

A modified method for estimation of total glycoprotein hexoses in feces, based on their measurements in the blood serum, is presented. Sixty-six nursing children with lactose intolerance, breastfed or formula fed, were examined; formula fed babies were kept on mixtures with high and low lactose content. Glycoprotein hexose parameters were as follows (X +/- m): 13.51 +/- 1.93, 12.05 +/- 2.20, and 3.69 +/- 0.47 g/l feces. In control children without lactose intolerance (n = 33) this value was 3.6 +/- 0.79 g/l. Increased glycoprotein excretion is connected with glycocalix and small intestinal enterocyte alteration.

Breast Feeding↗
PubMed1994

An adherens junction protein is a member of the family of lactose-binding lectins.

We previously described a pig junction protein of M(r) 37,000 found in oral epithelium but not in epidermis, limited to suprabasal cells, and colocalizing by immunofluorescence with adherens junction proteins. A 1.1-kilobase pair cDNA of the 37-kDa protein yielded an open reading frame encoding a 323-amino acid protein of 35,852 Da, and Northern analysis demonstrated a band of 1.2 kilobases in tongue RNA. Secondary structure predictions indicate that the 37% identical 16-17-kDa N- and C-terminal domains from beta-sheet-rich barrels linked by a compact proline-rich segment. The protein is 72% identical in amino acid sequence and shares symmetrical two-domain structure with L-36, a lectin of unknown function from rat intestine, indicating that the 37-kDa protein is the porcine form of L-36. Of the homologous lactose binding lectins known, two others, invertebrate lectins, share this symmetrical structure. Expression of the C-terminal domain of the pig lectin in bacteria yields a lectin which binds lactosyl-Sepharose, and binding is inhibited by lactose. The expressed protein binds a glycoprotein of 120 kDa from pig tongue epithelium on Western blots, and this is also inhibited by lactose. The findings suggest that the lectin function may be involved in the assembly of adherens junctions.

Amino Acid Sequence↗
PubMed1994

[The effects of the carbocalcitonin + arginine-lysine-lactose combination in senile involutional osteoporosis].

Numerous osteometabolic factors are implicated in the bone mass loss which occurs with ageing. Among these a significant role is played by the impairment of intestinal calcium absorption which may be attributed in the elderly to various factors such as the reduction of chlorhydro-peptic secretion, the correlated deficiency of vitamin D and their relative duodenal receptors. In order to evaluate the clinical efficacy of an arginine-lysine-lactose preparation a group of 40 subjects with senile involutional osteoporosis was studied. The subjects were divided into two groups using random criteria and were treated with carbocalcitonin alone (40 UMRC day i.m. on alternative days) or carbocalcitonin association complex. The following parameters were evaluated in basal conditions and after six months of treatment: bone mass density (BMD) using computerised bone mineralometry, bone pain, intake of analgesics, serum levels of calcium, phosphorus, alkaline phosphatase, osteocalcin, parathormone, as well as calciuria and hydroxyprolinuria. The comparison between the two groups shows a more marked increment in BMD in subjects treated with arginine-lysine-lactose, a greater reduction in painful symptoms, and a more evident and significant reduction of parathormone and hydroxyprolinuria levels. These effects appear to be due to a distinct improvement in intestinal calcium absorption mediated by lysine and lactose, and probably to a positive action played by the amino acid at the level of support structures.

Aged↗
PubMed1993

Soluble lactose-binding lectin from rat intestine with two different carbohydrate-binding domains in the same peptide chain.

Of the multiple soluble lactose-binding (S-Lac) lectins in rat intestine, the major one, tentatively designated RI-H, was previously isolated as a polypeptide of molecular weight approximately 17,000. We here report the sequence of RI-H, as determined both at the peptide level and at the nucleotide level. Surprisingly the cDNA encodes a protein of molecular weight approximately 36,000, and this protein contains two homologous but distinct domains each with sequence elements that are conserved among all S-Lac lectins. The C-terminal domain, designated domain II, corresponds to the lectin with M(r) of 17,000 previously isolated from intestinal extracts and shown to have lactose binding activity. By preparing recombinant protein containing only the N-terminal domain, designated domain I, we here directly demonstrate that it too binds lactose and a related range of sugars that are roughly similar to domain II, but clearly distinct. The new lectin, which we designate L-36, is highly expressed in full-length form in rat small and large intestine and stomach but was not detected in eight other tissues including lung, liver, kidney, and spleen. Each domain has approximately 35% sequence identity with the other domain and with the carbohydrate-binding domain of L-29, another S-Lac lectin, but only about 15% identity with other known S-Lac lectins.

Amino Acid Sequence↗
PubMed1997

Lactose intolerance in persistent diarrhoea during childhood: the role of a traditional rice-lentil (Khitchri) and yogurt diet in nutritional management.

Lactose intolerance is frequently encountered in children with persistent diarrhoea (PD). Selection of an appropriate milk-based formulation is a major management problem in the developing world. In a consecutive series of studies, we evaluated the role of feeding a traditional rice-lentil (khitchri) diet alone (KY) or in combination with either soy formula (KY-Soy) a dilute buffalo milk (KY-B), in children (age 6 months-3 years) with PD. Serial observations of stool output, caloric intake and weight gain of these children over a 14 day period indicated satisfactory tolerance of the KY diet with adequate weight gain. The weight gain and stool output was however higher in lactose intolerant children, with the worst results seen with K-Y and buffalo milk combination. While lactose intolerant children with PD do have higher. rates of therapeutic failure, our data indicates that a traditional diet and yogurt combination can be used satisfactorily for nutritional rehabilitation in over 80% of such children.

Animals↗
PubMedDate not supplied

[Lactose intolerance in hospitalized infants with acute diarrhea due to classic enteropathogenic Escherichia coil (EPEC)].

Three hundred and eleven hospitalized weaned infants with acute diarrhea, all under 12 months of age, were studied in order to evaluate the development of lactose intolerance and its association with age, nutritional status, birth weight, dehydration and enteropathogenic agents identified in fecal samples. After been rehydrated the infants received whole cow' milk assuring the intake of 100 kcal/kg per day. Lactose intolerance was defined according t the following criteria: 1) persistence of diarrhea associated with weight loss during 48 hours, 2) development of vomiting and/or abdominal distention associated with excretion of carbohydrate in feces and/or acids tools, 3) metabolic acidosis associated with abdominal distention at anytime of refeeding period. Lactose intolerance was detected in 52.1% (162/311) of the patients and it was significantly associated with age under 6 months (P < 0.01), birth weight under 3000 grams (P < 0.01), development of dehydration (P < 0.01) and with enteropathogenic Escherichia coli (EPEC) serotypes infection (P < 0.01).

Acute Disease↗
PubMed1979

[Milk intolerance in Colombian children, its prevalence and relation to lactose malabsorption].

A total of 121 children from an orphange were studied. Their ages ranged from 2 to 10 years and represented different ethnic backgrounds. The prevalence of malnutrition was 45% and their gastrointestinal symptomatology in response to graded amounts of milk intake was evaluated. None of the children complained when milk intakes were of 200 cc; 10% complained of gastrointestinal discomfort and/or diarrhea when 300 cc of milk (equivalent to 12 g of lactose) were administered, and 54% presented lactose malabsorption unrelated to ethnic background, sex or malnutrition. It is concluded that the prevalence of milk intolerance is minimal when milk is given in the usual amounts.

Age Factors↗
PubMed1985

The size of the lactose permease derived from rotational diffusion measurements.

The lactose permease of Escherichia coli was labeled with eosinyl-maleimide, reconstituted into vesicles of dimyristoylphosphatidylcholine and subjected to time-dependent phosphorescence anisotropy measurements in order to determine the rotational diffusion coefficient. By comparison with bacteriorhodopsin, the diffusion coefficient is evaluated in terms of an effective radius of the lactose permease in the plane of the membrane. This radius amounts to 20 +/- 2 A which implies that the lactose permease is a monomer. The monomeric state is maintained in the presence of a membrane potential.

Diffusion↗
PubMed1997

The role of helix VIII in the lactose permease of Escherichia coli: I. Cys-scanning mutagenesis.

Using a functional lactose permease mutant devoid of Cys residues (C-less permease), each amino acid residue in transmembrane domain VIII and flanking hydrophilic loops (from Gln 256 to Lys 289) was replaced individually with Cys. Of the 34 single-Cys mutants, 26 accumulate lactose to > 70% of the steady state observed with C-less permease, and an additional 7 mutants (Gly 262-->Cys, Gly 268-->Cys, Asn 272-->Cys, Pro 280-->Cys, Asn 284-->Cys, Gly 287-->Cys, and Gly 288-->Cys) exhibit lower but significant levels of accumulation (30-50% of C-less). As expected (Ujwal ML, Sahin-Tóth M, Persson B, Kaback HR, 1994, Mol Membr Biol 1:9-16), Cys replacement for Glu 269 abolishes lactose transport. Immunoblot analysis reveals that the mutants are inserted into the membrane at concentrations comparable to C-less permease, with the exceptions of mutants Pro 280-->Cys, Gly 287-->Cys, and Lys 289-->Cys, which are expressed at reduced levels. The transport activity of the mutants is inhibited by N-ethylmaleimide (NEM) in a highly specific manner. Most of the mutants are insensitive, but Cys replacements render the permease sensitive to inactivation by NEM at positions that cluster in manner indicating that they are on one face of an alpha-helix (Gly 262-->Cys, Val 264-->Cys, Thr 265-->Cys, Gly 268-->Cys. Asn 272-->Cys, Ala 273-->Cys, Met 276-->Cys, Phe 277-->Cys, and Ala 279-->Cys). The results indicate that transmembrane domain VIII is in alpha-helical conformation and demonstrate that, although only a single residue in this region of the permease is essential for activity (Glu 269), one face of the helix plays an important role in the transport mechanism. More direct evidence for the latter conclusion is provided in the companion paper (Frillingos S. Kaback HR, 1997, Protein Sci 6:438-443) by using site-directed sulfhydryl modification of the Cys-replacement mutants in situ.

Amino Acid Sequence↗
PubMed1994

Cloning and sequencing of the gene for the lactose carrier of Citrobacter freundii.

The gene coding for the lactose carrier of Citrobacter freundii was cloned into the plasmid pBR322. The gene was sequenced and the amino acid sequence was found to be 70% identical to the lactose carrier of E. coli. All of the charged residues in the membrane spanning region were conserved. The sugar specificity is somewhat different from that of E. coli. The C. freundii carrier has less activity for lactose and more activity for o-nitrophenyl-galactose (ONPG) than the carrier of E. coli.

Amino Acid Sequence↗
PubMed1998

Isolation and characterization of beta-galactoside specific lectin from Korean mistletoe (Viscum album var. coloratum) with lactose-BSA-sepharose 4B and changes of lectin conformation.

Lectins and its A- and B-chains from Korean mistletoe (Viscum album var. coloratum) were isolated by affinity chromatography on the Sepharose 4B modified by lactose-BSA conjugate synthesized by reductive amination of ligand (lactose) to epsilon-amino groups of lysine residues of spacer (BSA) after reduction by NaCNBH3. The lactose-BSA conjugate was coupled to Sepharose 4B activated by cyanogen bromide. The molecular weight determined by SDS-PAGE were a 31 kD of A-chain and a 35 kD of B-chain. Amino acid analysis and N-terminal sequencing were performed. The effects of pH, temperature and guanidine chloride on the conformation of the lectin were investigated by measuring its intrinsic fluorescence and compared with its hemagglutinating activities. Blue shift was detected on the acidic pH and there was a close relationship between activities and conformation of the lectin. Under denaturing conditions, the tryptophan emission profile of lectin showed typical denaturational red shift which also correspond to the conformations and activity of lectin.

Amino Acids↗
PubMed1990

Mechanism of enhanced melibiose transport rate catalyzed by an Escherichia coli lactose carrier mutant with leucine substituted for serine-306. The pH-dependence of melibiose efflux.

The mechanism of melibiose transport was studied in cells containing plasmid pAA22 which expresses the mutant lactose carrier (serine-306 to leucine) cloned from Escherichia coli AA22. These studies were of interest because several lines of evidence suggested that the AA22 mutation conferred novel properties upon the lactose carrier, decreasing turnover with several beta-galactoside substrates, increasing turnover with melibiose, and abolishing active accumulation even though equilibration occurred via symport with H+. Although severely defective in active melibiose accumulation, the present study indicates that in cells poisoned with azide the AA22 carrier does in fact equilibrate melibiose across the membrane more rapidly than the normal lactose carrier. Similarly, melibiose efflux from cells preloaded with melibiose was more rapidly catalyzed by the AA22 carrier than by the normal carrier (pH 7.0). Furthermore, although external H+ did reduce net melibiose efflux to a rate slower than seen in equilibrium exchange, a lower than normal pH was required to achieve this effect. Therefore, at pH 7.0, the AA22 carrier (but not the normal carrier) catalyzed net efflux at a rate approaching that for the exchange process (which was pH-resistant in both the mutant and the parent). At pH 8.0 both the AA22 carrier and the normal carrier catalyzed net melibiose efflux at a rate identical to the equilibrium exchange rate. We suggest (i) that the sensitivity of melibiose efflux to external pH indicates that during efflux the AA22 carrier interacts with protons in a manner similar to the normal carrier (i.e., sugar is cotransported with H+) and hence the absence of accumulation is not explained by internal leak via a binary carrier-melibose complex; and (ii) that the modest increase in rate constants for melibiose exit reflect small changes in activation energy (1 kcal/mol) consistent with a steric mechanism possibly involving van der Waals contacts.

Biological Transport↗
PubMed1985

Properties of a mutant lactose carrier of Escherichia coli with a Cys148----Ser148 substitution.

The cysteine residue at position 148 in the lactose carrier protein of Escherichia coli has been replaced by serine using oligonucleotide-directed, site-specific mutagenesis of the lac Y gene. The mutant carrier is incorporated into the cytoplasmic membrane to the same extent as the wild-type carrier, confers a lactose-positive phenotype on cells, and actively transports lactose and other galactosides. However, the maximum rate of transport for several substrates is reduced by a factor of 6-10 while the apparent affinity is reduced by a factor of 2-4. Carrier activity in the mutant is much less sensitive to sulfhydryl reagents (HgCl2, p-(chloromercuri)benzenesulfonate and N-ethylmaleimide) than in the wild type, and beta-D-galactosyl 1-thio-beta-D-galactoside does not protect the mutant carrier against slow inactivation by N-ethylmaleimide. It is concluded that the Cys148 residue is not essential for carrier-catalyzed galactoside: proton symport and that its alkylation presumbly prohibits access of the substrate to the binding site by steric hindrance. A serine residue at position 148 in the amino acid sequence appears to alter the protein structure in such a way that one or more sulfhydryl groups elsewhere in the protein become accessible to alkylating agents thereby inhibiting transport. Recently, Trumble et al. [(1984) Biochem. Biophys. Res. Commun. 119, 860-867] arrived at similar conclusions by investigating a mutant carrier with a Cys148----Gly148 replacement.

Amino Acid Sequence↗
PubMed2005

Sorbitol synthesis by an engineered Lactobacillus casei strain expressing a sorbitol-6-phosphate dehydrogenase gene within the lactose operon.

Sorbitol is claimed to have important health-promoting effects and Lactobacillus casei is a lactic acid bacterium relevant as probiotic and used as a cheese starter culture. A sorbitol-producing L. casei strain might therefore be of considerable interest in the food industry. A recombinant strain of L. casei was constructed by the integration of a d-sorbitol-6-phosphate dehydrogenase-encoding gene (gutF) in the chromosomal lactose operon (strain BL232). gutF expression in this strain followed the same regulation as that of the lac genes, that is, it was repressed by glucose and induced by lactose. (13)C-nuclear magnetic resonance analysis of supernatants of BL232 resting cells demonstrated that, when pre-grown on lactose, cells were able to synthesize sorbitol from glucose. Inactivation of the l-lactate dehydrogenase gene in BL232 led to an increase in sorbitol production, suggesting that the engineered route provides an alternative pathway for NAD(+) regeneration.

Gene Expression Regulation, Bacterial↗
PubMed1998

Lactose repressor protein: functional properties and structure.

The lactose repressor protein (LacI), the prototype for genetic regulatory proteins, controls expression of lactose metabolic genes by binding to its cognate operator sequences in E. coli DNA. Inducer binding elicits a conformational change that diminishes affinity for operator sequences with no effect on nonspecific binding. The release of operator is followed by synthesis of mRNA encoding the enzymes for lactose utilization. Genetic, chemical and physical studies provided detailed insight into the function of this protein prior to the recent completion of X-ray crystallographic structures. The structural information can now be correlated with the phenotypic data for numerous mutants. These structures also provide the opportunity for physical and chemical studies on mutants designed to examine various aspects of lac repressor structure and function. In addition to providing insight into protein structure-function correlations, LacI has been utilized in a wide variety of applications both in prokaryotic gene expression and in eukaryotic gene regulation and studies of mutagenesis.

Amino Acid Sequence↗
PubMed1997

Chromosomal insertion of the entire Escherichia coli lactose operon, into two strains of Pseudomonas, using a modified mini-Tn5 delivery system.

A 12-kb PstI fragment including the entire E. coli lactose operon (lacIPOZYA) was inserted in one copy into the chromosome of Pseudomonas putida, Pseudomonas fluorescens and an E. coli strain with lac- phenotype. This was made possible by improvements of an already existing mini-Tn5 transposon delivery system (de Lorenzo et al., 1990; Herrero et al., 1990), which integrates cloned DNA fragments at random sites on the chromosome of the recipient bacteria in single copies. This has resulted in: (a) the making of two useful low copy-number cloning vectors both with extensive multi-cloning regions flanked by NotI sites needed in the mini-Tn5 delivery system; (b) the generation of E. coli nonlysogenic strains expressing the pi protein thus being capable of maintaining and delivering R6K-based mini-Tn5 vectors to other E. coli strains; (c) the successful insertion of the E. coli lactose operon into the P. fluorescens chromosome giving P. fluorescens the ability to grow on lactose; (d) evidence from Southern blotting that contradicts the assumption that the mini-Tn5 delivery system always creates one-copy inserts. These improvements allow insertion of large DNA fragments encoding highly expressed proteins into the chromosome of a large variety of Gram-negative bacteria including E. coli.

Chromosomes, Bacterial↗