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At least 613 records · Page 34Linked to original sources
PubMed2005

Molecular and biochemical analysis of the galactose phenotype of dairy Streptococcus thermophilus strains reveals four different fermentation profiles.

Lactose-limited fermentations of 49 dairy Streptococcus thermophilus strains revealed four distinct fermentation profiles with respect to galactose consumption after lactose depletion. All the strains excreted galactose into the medium during growth on lactose, except for strain IMDOST40, which also displayed extremely high galactokinase (GalK) activity. Among this strain collection eight galactose-positive phenotypes sensu stricto were found and their fermentation characteristics and Leloir enzyme activities were measured. As the gal promoter seems to play an important role in the galactose phenotype, the galR-galK intergenic region was sequenced for all strains yielding eight different nucleotide sequences (NS1 to NS8). The gal promoter played an important role in the Gal-positive phenotype but did not determine it exclusively. Although GalT and GalE activities were detected for all Gal-positive strains, GalK activity could only be detected for two out of eight Gal-positive strains. This finding suggests that the other six S. thermophilus strains metabolize galactose via an alternative route. For each type of fermentation profile obtained, a representative strain was chosen and four complete Leloir gene clusters were sequenced. It turned out that Gal-positive strains contained more amino acid differences within their gal genes than Gal-negative strains. Finally, the biodiversity regarding lactose-galactose utilization among the different S. thermophilus strains used in this study was shown by RAPD-PCR. Five Gal-positive strains that contain nucleotide sequence NS2 in their galR-galK intergenic region were closely related.

Bacterial Proteins↗
PubMed1972

Biochemistry and genetics of galactose metabolism in group H Streptococcus strain Challis.

Galactose-negative mutants of the group H Streptococcus strain Challis were obtained by treatment with nitrosoguanidine. Enzyme assays of extracts of these mutants revealed that 12 of the mutants were lacking one of the enzymes of the Leloir pathway. Thus, the Leloir pathway is the major means of galactose metabolism in strain Challis. In addition, uridyl diphosphate galactose pyrophosphorylase, a permease function, and at least one other function are required for the utilization of galactose. The enzymes of the Leloir pathway are induced by galactose and fucose; no compounds which act as repressors of these enzymes have been found, although the system appears to be sensitive to catabolite repression. Transformation was used to map the mutants. The genes for galactose-1-phosphate uridyl transferase and glucose-4-epimerase appear to be closely linked. Within the transferase gene, six mutations have been mapped. The permease function and the undetermined functions are not linked to the Leloir pathway.

Carbon Isotopes↗
PubMed1977

Regulation of galactose oxidase synthesis and secretion in Dactylium dendroides: effects of pH and culture density.

The effects of pH and growth density on the amount of an extracellular enzyme, galactose oxidase, synthesized by the fungus Dactylium dendroides were studied. Growth at a pH below 6.7 caused a decrease in the ability of the organism to release galactose oxidase. The enzyme retained by these fungal cells was liberated whenever the pH was raised to 7.0. Cycloheximide addition failed to inhibit the appearance of this protein; [3H]leucine added prior to pH adjustment was not incorporated into the released protein, These observations indicate the released protein is not newly synthesized protein. The retained enzyme would be secreted slowly over a 2-day period if the pH was not increased. In addition to regulating protein retention, pH was also shown to be associated with vacuolization, cell volume, culture density, and inhibition of protein synthesis. Cultures maintained at low pH were characterized by a dense growth consisting of highly vacuolated, buoyant, fungal hyphae. Increasing the pH from 6 to 7 caused a decrease in vacuole size. Cells grown at neutral pH maintained a lower density of growth and, based on activity measurements, synthesized 33% more galactose oxidase. Furthermore, cultures grown at pH 6.0 and maintained at a lower cell density produced galactose oxidase at a level similar to that of cells grown at neutral pH. Thus, the elevated density of the cell culture was inhibitory to galactose oxidase synthesis. The observed effects on protein synthesis and release were rather specific for galactose oxidase, since other extracellular proteins appeared in the earliest stages of growth.

Alcohol Oxidoreductases↗
PubMed2003

Characterization, expression, and mutation of the Lactococcus lactis galPMKTE genes, involved in galactose utilization via the Leloir pathway.

A cluster containing five similarly oriented genes involved in the metabolism of galactose via the Leloir pathway in Lactococcus lactis subsp. cremoris MG1363 was cloned and characterized. The order of the genes is galPMKTE, and these genes encode a galactose permease (GalP), an aldose 1-epimerase (GalM), a galactokinase (GalK), a hexose-1-phosphate uridylyltransferase (GalT), and a UDP-glucose 4-epimerase (GalE), respectively. This genetic organization reflects the order of the metabolic conversions during galactose utilization via the Leloir pathway. The functionality of the galP, galK, galT, and galE genes was shown by complementation studies performed with both Escherichia coli and L. lactis mutants. The GalP permease is a new member of the galactoside-pentose-hexuronide family of transporters. The capacity of GalP to transport galactose was demonstrated by using galP disruption mutant strains of L. lactis MG1363. A galK deletion was constructed by replacement recombination, and the mutant strain was not able to ferment galactose. Disruption of the galE gene resulted in a deficiency in cell separation along with the appearance of a long-chain phenotype when cells were grown on glucose as the sole carbon source. Recovery of the wild-type phenotype for the galE mutant was obtained either by genetic complementation or by addition of galactose to the growth medium.

Base Sequence↗
PubMed1999

The Gal3p-Gal80p-Gal4p transcription switch of yeast: Gal3p destabilizes the Gal80p-Gal4p complex in response to galactose and ATP.

The Gal3, Gal80, and Gal4 proteins of Saccharomyces cerevisiae comprise a signal transducer that governs the galactose-inducible Gal4p-mediated transcription activation of GAL regulon genes. In the absence of galactose, Gal80p binds to Gal4p and prohibits Gal4p from activating transcription, whereas in the presence of galactose, Gal3p binds to Gal80p and relieves its inhibition of Gal4p. We have found that immunoprecipitation of full-length Gal4p from yeast extracts coprecipitates less Gal80p in the presence than in the absence of Gal3p, galactose, and ATP. We have also found that retention of Gal80p by GSTG4AD (amino acids [aa] 768 to 881) is markedly reduced in the presence compared to the absence of Gal3p, galactose, and ATP. Consistent with these in vitro results, an in vivo two-hybrid genetic interaction between Gal80p and Gal4p (aa 768 to 881) was shown to be weaker in the presence than in the absence of Gal3p and galactose. These compiled results indicate that the binding of Gal3p to Gal80p results in destabilization of a Gal80p-Gal4p complex. The destabilization was markedly higher for complexes consisting of G4AD (aa 768 to 881) than for full-length Gal4p, suggesting that Gal80p relocated to a second site on full-length Gal4p. Congruent with the idea of a second site, we discovered a two-hybrid genetic interaction involving Gal80p and the region of Gal4p encompassing aa 225 to 797, a region of Gal4p linearly remote from the previously recognized Gal80p binding peptide within Gal4p aa 768 to 881.

Adenosine Triphosphate↗
PubMed1986

Hepatic blood flow: accuracy of estimation from galactose clearances in cats.

Experiments were carried out to determine the accuracy and validity of estimations of hepatic blood flow from clearance data during infusions of galactose in anesthetized cats. Clearance calculations were compared directly with the measured hepatic blood flows using a hepatic venous long-circuit technique. This technique allowed direct measurement and alteration of hepatic blood flow and collection of arterial and mixed hepatic venous blood samples without depletion of the animal's blood volume. It was found that infusions of galactose could not be used to estimate accurately hepatic blood flow. Infusion rate could not be used as an estimate of hepatic or splanchnic uptake owing to substantial and variable extrasplanchnic uptake. As a result, estimated hepatic flows allowing for incomplete extraction overestimated the true flow. On the other hand, extraction was less than 100%. This caused systemic galactose clearance to underestimate hepatic blood flow. These errors could cancel each other giving an apparently good estimate of hepatic flow from systemic galactose clearance. This agreement was fortuitous and occurred only at a specific dose and blood flow. We conclude that in the absence of independent measurements of both extrasplanchnic uptake and splanchnic extraction of galactose, systemic galactose clearance is not a reliable measure of hepatic blood flow in anesthetized cats. Until proved otherwise, it seems likely that this is also true in humans.

Animals↗
PubMed1989

Changes in hepatic blood volume on galactose and indocyanine green uptake by cat liver.

The liver has important functions as a blood volume reserve and in uptake and metabolism of many substrates. This study examines whether changes in hepatic blood volume modify the uptakes of model substrates galactose and indocyanine green (ICG) in cats anesthetized with pentobarbital sodium. A hepatic venous long-circuit technique with an extracorporeal reservoir was used to control hepatic flow and venous pressure and to allow repeated sampling of arterial, portal, and hepatic venous blood without depletion of the cat's blood volume. Hepatic blood volume was measured by plethysmography. Galactose and ICG were infused intravenously at constant rates for 200 min in each of three series of experiments. The first series were time controls. In the second series, hepatic blood volume was increased by raising hepatic venous pressure. In the third series hepatic blood volume was decreased by hepatic nerve stimulation and infusions of norepinephrine and angiotensin. Hepatic congestion resulted in small increases in blood galactose levels, suggesting mild impairment of hepatic galactose metabolism. Decreases in liver blood volume did not modify hepatic galactose metabolism. Increases in hepatic blood volume facilitated while decreases inhibited ICG uptake, but the effects were small. Sinusoidal velocity and transit time have minor effects on uptake even for protein-bound substrates. In summary, large changes in hepatic blood volume had minor effects on galactose and ICG blood concentrations, suggesting that the metabolic functions of the liver are essentially independent of the blood reservoir function.

Animals↗
PubMed1996

Early glycogenolysis and late glycogenesis in human liver after intravenous administration of galactose.

Galactose is incorporated by a different metabolic pathway than glucose. Its contribution to glycogen synthesis has not been studied in humans. We administered galactose (0.5 g/kg iv) to overnight-fasted normal human volunteers and examined its effects on hepatic glycogen synthesis and hepatic glucose output (HGO). Hepatic glycogenesis was assessed noninvasively, determining glycogen concentration by 13C magnetic resonance spectroscopy (MRS) and liver volume by magnetic resonance imaging. HGO was determined by [6,6-2H2]glucose and gluconeogenesis calculated by adding the amount of hepatic glycogenesis to the HGO. After galactose administration, liver glycogen concentration (baseline 254 +/- 11 mmol/l) decreased in the first 45 min to 207 +/- 15 mmol/l (P < 0.05) and increased thereafter to 313 +/- 7 mmol/l (P < 0.01). Net hepatic glycogenesis was 101 +/- 12 mmol over 150 min. HGO (baseline 14.3 +/- 1.9 mumol.kg-1.min-1) increased threefold in the first 15 min and then returned to baseline. The average rate of gluconeogenesis was 12.3 mumol.kg-1.min-1. Intravenous galactose leads to an increase in hepatic glycogen and hepatic glucose output in normal humans. Competitive inhibition of UDP-glucose pyrophosphorylase by UDP-galactose could explain the apparent glycogenolysis observed early after galactose administration. 13C MRS in combination with a stable isotope tracer is a noninvasive and safe method to study hepatic carbohydrate metabolism in humans.

Adult↗
PubMed1989

Galactose feeding causes glomerular hyperperfusion: prevention by aldose reductase inhibition.

Experimental dietary galactosemia is known to result in accumulation of the polyol, galactitol, via the aldose reductase metabolic pathway in a variety of tissues, including renal glomeruli. Because increased polyol accumulation also occurs in insulin-dependent diabetes mellitus (IDDM), in which marked renal glomerular hyperperfusion occurs, we have studied glomerular hemodynamics in rats with experimental galactosemia. Insulin deficiency and its accompanying metabolic disorders are not present in this experimental model. In additional groups of animals, aldose reductase inhibitors, either sorbinil or tolrestat, were added to the galactose diet. In all, five groups of rats were studied: regular diet, 50% galactose diet, regular diet plus sorbinil, 50% galactose diet plus sorbinil, and 50% galactose plus tolrestat. The diets were comparable in protein and salt, and the rats were pair fed. Micropuncture and whole kidney clearance measurements were carried out after 10-14 days on these diets. Compared with rats fed the regular diet, those fed with 50% galactose diet had significantly higher glomerular filtration rates, renal plasma flow, single-nephron glomerular filtration rates, and plasma flow (QA), whereas afferent vascular resistance (RA) was decreased. Addition of sorbinil or tolrestat to the high-galactose diet not only prevented renal hyperperfusion but RA and single-nephron filtration fraction (SNFF) were higher than in normal rats, and QA was lower. In addition, sorbinil administration to rats on the control diet caused significant decreases in single-nephron blood flow and the ultrafiltration coefficient and a rise in SNFF.(ABSTRACT TRUNCATED AT 250 WORDS)

Aldehyde Reductase↗
PubMed1987

Metabolic studies of a sustained galactose overload in rat.

In order to obtain an experimental model for studying inherited disorders of galactose metabolism in man, we administered to adult rats a diet supplemented with 50% of galactose during 38 days. The results showed clinical symptoms such as polyuria, polydipsia, growth retardation and bilateral cataract. The main biochemical features were an increase in the galactokinase and uridyltransferase activities in liver, an ubiquitous accumulation in tissues and a considerable urinary elimination of galactose and galactitol, a weak accumulation of galactose-1-phosphate in tissue and a hyperaminoaciduria. This work led us to quantify the respective importance of the major pathway and minor pathways of galactose in the rat after a galactose-rich diet.

Animals↗
PubMed1978

14C-D-galactose breath test for evaluation of liver function in patients with chronic liver disease.

D-Galactose metabolism and demethylation of aminopyrine by healthy controls and patients with chronic active hepatitis (CAH) and cirrhosis (Ci), were assessed by a breath analysis technique measuring 14CO2 exhalation after oral ingestion of 14C-D-galactose or 14C-aminopyrine. Patients with CAH and Ci exhibited decreased 14CO2-exhalation rates following 14C-D-galactose or 14C-aminopyrine. D-Galactose oxidation capacity of the liver can be assessed by a breath analysis technique in analogy to the demethylating function for aminopyrine. The ordinary oral D-galactose tolerance test seems, however, superior in comparison to the 14C-D-galactose tolerance test, in discriminating between healthy controls and patients with chronic liver disease.

Administration, Oral↗
PubMed1992

Assessment of liver function using a novel galactose single point method.

A novel, simple, clinically useful quantitative liver function test, called the galactose single point (GSP) method, was developed by measurement of galactose blood concentration 1 h after galactose was administered (0.5 g/kg). It was quickly infused intravenously in 55 normal healthy volunteers, 73 patients with chronic hepatitis (CH), 36 with cirrhosis and 41 with hepatocellular carcinoma (HCC). Patients with CH diagnosis were assessed by liver biopsy. Cirrhosis was diagnosed by histological examination or a chronic hepatitis history with esophageal varices or ascites, whereas HCC was diagnosed either histologically, or cytologically proved, or as implied in the 'one imagine study' being positive with AFP > 300 ng/dl. Highly significant galactose blood levels were observed between normal healthy volunteers and patients 50, 60 and 70 min after galactose was administered. Galactose elimination capacity (GEC), modified GEC (MGEC) and consecutive GSP tests were performed in 6 healthy volunteers for 2 days. 0.64-16.87% variation was observed for each subject. The significant differences (p < 0.001) in average GSP values were 247 +/- 18.1, 422 +/- 27.3, 629 +/- 42.8 and 579 +/- 43.6 micrograms/ml for normal healthy volunteers, CH, cirrhosis and HCC patients, respectively. Highly significant correlations (p < 0.001) were obtained among GSP, GEC and MGEC for all patients. Positive correlations were observed between GSP, GEC, MGEC and AST (serum aspartate aminotransferase), ALT (serum alanine aminotransferase), serum bilirubin, albumin, prothrombin time and r-globulin. According to results obtained from 202 normal healthy volunteers and patients, the GSP method may be a simple, clinically useful quantitative measurement of liver function for the determination of a patient's residual liver function, the prognosis of liver function for patients with cirrhosis, postoperational follow-up and, finally, the timing of a liver transplant.

Adult↗
PubMed1988

Patterns of serum glucose and galactose concentrations in term newborn infants after milk feeding.

Galactose and glucose concentrations were measured in peripheral blood in relation to ad libitum milk feeding in 11 healthy near-term infants. Galactose and glucose concentrations before feeding averaged 1.06 +/- 0.21 and 60.3 +/- 3.2 mg/dl, respectively. After feedings containing 0.76-2.68 g lactose/kg body weight, both galactose and glucose rose by approximately 35% Galactose concentrations rose by 0.72 +/- 0.10 mg/dl at 30 min after feeding, while glucose concentration rose by 23.3 +/- 2.5 mg/dl at 30 min after feeding. The 25-fold greater absolute increase in the concentration of glucose than galactose is consistent with efficient first-pass clearance of galactose by the neonatal liver.

Analysis of Variance↗
PubMed1983

Scanning electron microscopy of X-ray-induced cataract in mice on normal and galactose diet.

The possible multiple effect of galactose diet and X-irradiation on cataract development in mice was investigated by scanning electron microscopy. X-ray cataracts were induced by maintaining animals either on a normal or 50% galactose diet. No detectable changes in lens morphology were seen in animals fed galactose alone compared with normal controls. 2 months after X-ray, less damage had occurred to the lenses of the galactose-fed animals compared to those on a normal diet. At 4 months after X-ray, animals on a normal diet developed mature cataracts, while in the galactose-fed animals they were delayed by 0.5-1.5 months. Suppression of the development of X-ray cataract by galactose feeding may be related to the ability of this sugar, which accumulates in mouse lens due to the low levels of aldose reductase, to act as a free radical scavenger.

Animals↗
PubMed1987

Effect of prolactin on galactose cataractogenesis.

Prolactin has been known to affect the water and electrolyte balance. Because increased lens hydration has been shown to be a common phenomenon in most, if not all types of cataracts, we have been interested in investigating a possible role of prolactin in sugar cataract induction and progression. For this study, we have used morphological and biochemical approaches. The prolactin delivery method involved intraperitoneal implantation of one or more pellets in Sprague-Dawley female rats. Following implantation of the desired number of prolactin or control (nonprolactin) pellets, animals were either fed galactose and lab chow, or lab chow diet. Gross morphological observations of whole lenses, slit-lamp examination of lenses and light microscopic analysis of lens sections showed that in the galactose-fed prolactin group, galactose associated alteration progressed faster and total opacification (mature cataract development) was achieved earlier than in the nonprolactin group. The levels of galactose and dulcitol were higher in the lenses of galactose-fed prolactin treated rats as compared to lenses from nonprolactin (control) rats. No significant difference in lens Na+-K+ ATPase activity between the prolactin and nonprolactin group was observed. Our results indicate that prolactin accelerates galactose-induced cataractogenesis in rats.

Animals↗
PubMed1989

Effect of uridine on hepatic galactose-1-phosphate uridyltransferase.

Uridine sugar nucleotides are important intermediates in galactose metabolism and may play a role in the long-term galactose toxicity in human galactose-1-phosphate uridyltransferase deficiency galactosemia. Since administration of uridine, a precursor of uridine nucleotides, has been considered as a therapeutic measure, we have investigated the effects of this compound on the activity of rat hepatic transferase. Uridine has been found to be an inhibitor of the enzyme in in vitro studies and to cause an increase in galactose-1-phosphate in liver perfused with galactose which is consistent with physiologic inhibition of the enzyme. Uridine is a partial linear competitive inhibitor of UDPglucose and an uncompetitive inhibitor of galactose-1-phosphate. These findings suggest caution should be applied in giving the compound to subjects with genetically limited transferase activity because of the possibility of inhibiting the small amount of residual enzyme.

Aging↗
PubMed1973

On the uptake of materials by the intact liver. The transport and net removal of galactose.

D-galactose, a monosaccharide rapidly phosphorylated within liver cells, is irreversibly removed from the portal circulation. We have studied the kinetic relations between the hepatic cell entry process and the metabolic sequestration process, by means of the multiple indicator dilution technique. Labeled red blood cells (a vascular indicator), labeled sucrose (an extracellular reference), and labeled galactose were rapidly injected into the portal vein, and from rapidly sampled hepatic venous blood, normalized outflow-time patterns were secured. The labeled red cell curve rises to the highest and earliest peak, and decays rapidly; and that for labeled sucrose rises to a later and lower peak. Its extrapolated recovery is equivalent to that of the labeled red cells. At low blood galactose concentrations, the labeled galactose appears at the outflow with labeled sucrose, but is much reduced in magnitude, and exhibits a long tailing. Its outflow recovery is much reduced. At high blood galactose concentrations, the initial part of the profile increases towards that for labeled sucrose, the tailing becomes much larger in magnitude, and the outflow recovery becomes virtually complete. We have modeled the uptake of labeled galactose, and find two parts to the predicted outflow pattern, corresponding to our experimental observations; throughput material, which sweeps past the cell surface in the extracellular space; and returning material, which has entered the cells but escaped the sequestration process. Analysis of the data by use of this model provides estimates of both transmembrane fluxes and rates of sequestration. The capacity of the process subserving cell entry is found to be 40 times that for phosphorylation; and, whereas the K(m) value for sequestration is less than 15 mg/100 ml, that for entry is approximately 500 mg/100 ml. Both processes are relatively stereospecific; the entry of the L-stereoisomer is very slow and it undergoes no significant amount of metabolic sequestration. The sequestration process produces a lobular intracellular concentration gradient; and this gradient, in turn, produces some uncertainty in the estimate of the true K(m) value for the sequestration process.

Animals↗
PubMed1984

Resistance of the male gonad to a high galactose diet.

Rats were fed a 50% galactose diet during pregnancy and nursing, and the testes were later examined and hormone levels determined in male offspring. Exposure to galactose for various periods during pregnancy, throughout the entire gestation, or postnatally to nursing mother until pups were 5 wk of age produced no significant differences from control testicular weight, seminiferous tubular diameter, or microscopic appearance of the testis when the offspring became adult (66 or 127 d). Serum luteinizing hormone, follicle stimulating hormone, and testosterone levels were determined 127 d postnatally and no significant differences from controls were observed in any of the treatment groups. Blood galactose-1-phosphate levels in animals receiving the 50% galactose diet were comparable to levels observed in human galactosemia. The resistance of the rat testis to a high galactose diet is consistent with the infrequency of testicular insufficiency in human galactosemia, and contrasts with the prenatal female gonadal sensitivity to galactose previously demonstrated in the rat and the high frequency of ovarian failure in human galactosemia.

Animals↗