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Query: KEGG:D00046 (lactose)
 16,692 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Growth of Escherichia coli strain MM6-13 (ptsI suc lacI sup), which as a suppressor of the succinate-negative phenotype, was inhibited by lactose. Cells growing in yeast extract-tryptone-sodium chloride medium (LB broth) were lysed upon the addition of lactose. In Casamino Acids-salts medium, lactose inhibited growth, but due to the high K+ content no lysis occurred. Lysis required high levels of beta-galctosidase and lactose transport activity. MM6, the parental strain of MM6-13, has lower levels of both of these activities and was resistant to lysis under these conditions. When MM6 was grown in LB broth with exogenous cyclic adenosine monophosphate, however, beta-galactosidase and lactose transport activities were greatly increased, and lysis occurred upon the addition of lactose. Resting cells of both MM6 and MM6-13 were lysed by lactose in buffers containing suitable ions. In the presence of MG2+, lysis was enhanced by 5 mM KCl and 100 mM NaCl. Higher slat concentrations (50 mM KCl or 200 mM NaCl) provided partial protection from lysis. In the absence of Mg2+, lysis occurred without KCl. Lactose-dependent lysis occurred in buffers containing anions such as sulafte, chloride, phosphate, or citrate; however, thiocyanate or acetate protected the cells from lysis. These data indicate that both cations and anions, as well as the levels of lactose transport and beta-galactosidase activity, are important in lysis.
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PMID:Lysis of Escherichia coli mutants by lactose. 4 Sep 61

Lactic streptococci, classically regarded as homolactic fermenters of glucose and lactose, became heterolactic when grown with limiting carbohydrate concentrations in a chemostat. At high dilution rates (D) with excess glucose present, about 95% of the fermented sugar was converted to l-lactate. However, as D was lowered and glucose became limiting, five of the six strains tested changed to a heterolactic fermentation such that at D = 0.1 h(-1) as little as 1% of the glucose was converted to l-lactate. The products formed after this phenotypic change in fermentation pattern were formate, acetate, and ethanol. The level of lactate dehydrogenase, which is dependent upon ketohexose diphosphate for activity, decreased as fermentation became heterolactic with Streptococcus lactis ML(3). Transfer of heterolactic cells from the chemostat to buffer containing glucose resulted in the nongrowing cells converting nearly 80% of the glucose to l-lactate, indicating that fine control of enzyme activity is an important factor in the fermentation change. These nongrowing cells metabolizing glucose had elevated (ca. twofold) intracellular fructose 1,6-diphosphate concentrations ([FDP](in)) compared with those in the glucose-limited heterolactic cells in the chemostat. [FDP](in) was monitored during the change in fermentation pattern observed in the chemostat when glucose became limiting. Cells converting 95 and 1% of the glucose to l-lactate contained 25 and 10 mM [FDP](in), respectively. It is suggested that factors involved in the change to heterolactic fermentation include both [FDP](in) and the level of lactate dehydrogenase.
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PMID:Change from homo- to heterolactic fermentation by Streptococcus lactis resulting from glucose limitation in anaerobic chemostat cultures. 10 49

The gluconeogenic capacity of mammary tissue of lactating cow was investigated by incubating mammary tissue slices with alanine, glutamate, lactate, pyruvate, or glycerol in conjunction with acetate and glucose (10mM or 1 mM). In no case was any substrate incorporated into glucose per se. In lactose synthesis, glucose was the major source of carbon although glycerol also was incorporated into lactose. Alanine, glutamate, lactate, or pyruvate were not incorporated into lactose at optimum (10 mM) or suboptimum (1 mM) concentrations of glucose. Activity of glucose-6-phosphatase was negligible in mammary tissue, less than 1% of the activity in liver or kidney tissue from the same cows. Pyruvate carboxylase, phosphoenolpyruvate carboxykinase, and fructose-1,6-diphosphatase were in cow mammary tissue, but the activities were lower than in liver. Gluconeogenic substrates were not converted to glucose regardless of whether the incubation contained an optimum (10 mM) or a suboptimum (1 mM) glucose concentration. Consistent with the inability of cow mammary tissue to convert gluconeogenic metabolites to glucose is the virtual absence of glucose-6-phosphatase and the lack of excess gluconeogenic substrates available to the intact mammary gland of lactating cow.
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PMID:Cellular gluconeogenesis by lactating bovine mammary tissue. 17 3

The major beta-galactosidase of rabbit brain has been purified over 400-fold. The enzyme converts G-M-1-ganglioside; Gal beta-1 yields 3 GalNAc beta-1 yields 4 (NANalpha-2 yields 3) Gal beta-1 yields 4 Glc yields ceramide (G-M-1) into Tay Sachs ganglioside GalNAc beta-1 yields 4 (NANalpha-2 yields 3) Gal beta-1 yields 4 Glc yields ceramide (G-M-2-ganglioside) and ceramide lactoside, Gal beta-1 yields 4 Glc yields ceramide (Gal-Glc-Cer) into glucocerebroside, Glc yields ceramide (Glc-Cer). The enzyme also hydrolyzes the synthetic substrates NPh-Gal and MeUmb-Gal. It is eluted as a single peak from Sephadex G-200 columns when natural and synthetic substrates were used and has an isoelectric point of 6.3. We were unable to resolve activity towards G-M-1-ganglioside and Gal-Glc-Cer by polyacrylamide electrophoresis in two buffer systems. With G-M-1 the pH optimum was 4.3 in acetate buffer and the K-m value 78 mu-M while with Gal-Glc-Cer, a pH optimum of 4.5 and a K-m of 17 mu-M were found. Hydrolysis of both natural and synthetic substrates was inhibited by gamma-D-galactonolactone, D-galactose and lactose. The data strongly suggest that a single beta-galactosidase hydrolyzes all the substrates tested.
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PMID:Purification of G-M-1-ganglioside and ceramide lactoside beta-galactosidase from rabbit brain. 23 52

The action of Clostridium perfringens neuraminidase on the ganglioside Gm1 tritiated in the ceramide moiety was studied. The rates of hydrolysis of the Gm1 ganglioside were determined from radioactivity in the neutral glycolipid product, which was separated from the substrate on DEAE-Sephadex columns. In order to study the physical state of the substrate in the conditions used in the neuraminidase treatment, the critical micelle concentrations of the Gm1 ganglioside were determined using formation of the triiodide anion in aqueous iodine solution as an indicator. The critical micelle concentrations were also obtained by determining the non-sedimenting radioactivity at different concentrations of the labeled ganglioside per total volume used in ultracentrifugation experiments. In addition, the concentrations of the monomeric ganglioside were concluded from the results of the ultra-centrifugation studies. The increase in the reaction rate of the Gm1 hydrolysis as the function of the substrate concentration was leveled off at 25-28 microM ganglioside. The abrupt change at this concentration is interpreted as reflecting the monomer-micelle transition of the ganglioside in the conditions used (50mM sodium acetate buffer, pH 4.6). The critical micelle concentration was 29 microM on the basis of the triiodide test, and ultracentrifugation revealed the critical micelle concentration 28 microM. The reaction velocity of the hydrolysis was decreased immediately above the critical micelle concentration, and became constant at higher concentrations of the ganglioside. A close correlation to these changes in the reaction rate is suggested to exist in the concentrations of the monomeric Gm1 ganglioside. Saturation of the buffer used in the neuraminidase assays with butanol effected a striking change in the plot of reaction rate versus ganglioside concentration. The reaction rate increased up to 100-110 microM Gm1 ganglioside. The shift of the inflexion point in the rate plot from 25-28 microM to 100-110 microM ganglioside concentration is suggested to be due to a respective change in the critical micelle concentration effected by butanol. N-Acetylneuraminyllactosyl ceramide, lactosyl ceramide and asialo-Gm1 ganglioside had an inhibitory effect on the reaction. In contrast, N-acetylneuraminyllactose, lactose and some other free saccharides were not inhibitory. The results demonstrate that factors other than the saccharide structure must be taken into account when substrate specificity of a glycosidase is studied using competition experiments. It is suggested that the inhibition effected by the glycolipids is due to an increase in the micellar state of the Gm1 ganglioside.
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PMID:Monomer-micelle transition of the ganglioside GM1 and the hydrolysis by Clostridium perfringens neuraminidase. 46 31

The rate of gastric emptying was determined in three-day old suckling rats. The gastric loads were given by gavage, and, after from 5 to 100 min, emptying was determined by removing the stomach and weighing the contents. Results were expressed as percentage of load still remaining in the stomach at one hour. The gastric loads in increasing order of speed of emptying were 1.0 M Na acetate, heavy cream, 0.5 M NaCl, milk, corn oil, 0.15 M lactose, 0.3 M glucose, 0.15 M NaCl, acidic water, and water. The rate of emptying was compared to the effectiveness in previous experiments of the same gastric loads in depressing intake. There was no significant correlation between rate of gastric emptying of the loads and their effectiveness in producing satiety. The octapeptide of cholecystokinin (80 Ivy dog units or 2.7 micrograms/kg i.p.) significantly depressed intake (measured as weight gain) of suckling rats of 1 1/2 hours, but the same dose did not slow gastric emptying. These findings indicate that rate of gastric emptying does not determine satiety in the suckling rat.
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PMID:Gastric emptying and cholecystokinin in the control of food intake in suckling rats. 52 49

Pregnant rats were subjected to oophorectomy and hysterectomy (O-H) on the seventeenth day of pregnancy, a time when serum levels of prolactin, estrogen, and corticosterone are not substantially greater than the respective levels in nonpregnant rats. At 32 hours after O-H, serum prolactin and corticosterone both rose more than threefold, and lactose appeared in the mammary glands. Biopsies of mammary tissue obtained at 8 hour intervals after O-H showed a progressive secretory response over 16 hours, similar to that previously shown to occur within a period of about 4 hours on the last day of pregnancy. Suppression of serum prolactin by ergocriptine administration and adrenalectomy 24 hours before O-H each prevented the secretory response. However, some differences in the effects of deprivation of the two types of hormones were evident. After cortisol acetate administration at O-H, mammary tissue responded rapidly despite adrenalectomy 24 hours earlier. It is concluded that simple withdrawal of progesterone is not sufficient to initiate lactation in the pregnant rat; glucocorticoids must be present continuously during progesterone withdrawal, and prolactin elevation and other factors present at parturition may be required as well.
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PMID:Ultrastructural alterations in mammary glands of pregnant rats after ovariectomy and hysterectomy: effect of adrenal steroids and prolactin. 58 22

1. The changes in mammary function following cessation of milking during declining lactation have been studied in conscious goats. 2. No significant changes in the rate of milk secretion, mammary blood flow or metabolism occurred in the first 24 h after cessation of milking. After then, secretory rate, mammary blood flow, oxygen consumption, glucose uptake and acetate uptake decreased markedly over the next 3 days. Up to the time of maximum udder distension on day 3, there were no major changes in milk composition. 3. It was found that the rate of milk secretion declined when the calculated pressure within the alveoli became positive. 4. After 3 days, mammary volume and intramammary pressure decreased, and the composition of milk changed slowly to resemble that of extracellular fluid, i.e. [Na+], [Cl-], [HCO3-] and pH increased while [K+], [lactose] and [citrate] decreased. During this time [lactose] and [K+] were positively correlated, and [lactose] and [Na+], and [lactose] and [Cl-] negatively correlated. 5. It is suggested that the changes in milk composition, the decreases in mammary volume and in intramammary pressure after day 3 are due to the loss of integrity of the mammary epithelium. 6. By about 7 weeks after the cessation of milking the udder volume was less than the empty udder volume before milking was stopped, indicating a loss of mammary tissue as well as the resorption of fluid. 7. When milking of an autotransplanted gland was stopped, while milking of the control gland in situ was continued, the rate of secretion in the transplant fell while that of the control did not change. 8. In goats milked normally but in which a volume of isosmotic lactose equal to the volume of milk removed at that milking was injected into the lumen of one gland at each milking, the rate of secretion of that gland, but not that of the other, decreased.
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PMID:Mammary function and its control at the cessation of lactation in the goat. 67 60

Human milk contains large amounts of the iron-binding protein lactoferrin. This is normally unsaturated with iron. It also contains large amounts of IgA and small amounts of IgG and IgM. A combination of lactoferrin and specific antibody has a powerful bacteriostatic effect on Escherichia coli. In sucking infants the milk proteins probably reach the small intestine intact. Experiments with sucking guinea pigs show that milk suppresses E. coli in the gut and that the unsaturated iron-binding protein plays an essential role in the bacteriostatic reaction. Inhibited E. coli appear to be acutely iron deficient. E. coli growing slowly in iron-deficient media show abnormal forms of certain aminoacyl tRNAs. In bacteria inhibited by colostrum the proportion of abnormal tRNA is as high as 90%. These abnormal tRNAs are converted to the normal form by the addition of iron. This occurs in the absence of further RNA synthesis and is accompanied by renewed bacterial growth. The normal flora of the gut also plays an important role in resistance. Human milk has a low buffering capacity and bacterial fermentation of lactose produces a low pH.e. coli is inhibited by acetic acid/acetate buffer at pH 4.8-5.6, whereas these conditions allow normal growth of Lactobacillus bifidus. The faeces of babies fed on breast milk have a low pH, low counts of E. coli and high counts of L. bifidus. Artificially fed babies have more alkaline faeces which contain few L. bifidus and large numbers of E. coli.
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PMID:Iron-binding proteins and other factors in milk responsible for resistance to Escherichia coli. 79 96

A study was made of 239 strains of enteropathogenic escherichia 0151:K-- isolated in various regions of the USSR from patients with the clinical diagnosis of dysentery, gastroenteritis, intestinal coli-infection: a standard strain of the international collection of escherichia belonging to the given serological group was also studied. There was shown an increase in the role of these microorganisms among the enteropathogenic escherichia recorded at the territory of the USSR; they occupied the third place by the frequency of isolation after the serological group 0124:K72 and 0111:K58. There was established a common nature of the enzymatic characteristics of escherichia 0151:K--with shigellae by the absence of lactose, sucrose, inosite, adonite fermentation, the presence of gasless, immobile variants containing no lysin decarboxylase, and a possibility of rapid differentiation from shigellae in the use of acetate medium. Among the escherichia 0151:K--there was revealed the presence of 5 biotypes by the capacity to gas-formation in glucose, arabinose, sorbit, dulcit fermentation, and decarboxylation of lysin and ornithin; three biotypes are described for the first time. Industrial issue of the agglutinating serum 0151:K--is necessary to provide the diagnosis of these microorganisms at the territory of the USSR.
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PMID:[Biological characteristics of enteropathogenic escherichia of serologic group 015:K]. 79 86


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