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PubMed1972

Multiple regulator gene control of the galactose operon in Escherichia coli K-12.

Previous studies showed that nonsense mutations in either of two genes (capR or capS) or an undefined mutation in a third gene (capT) led to pleiotropic effects: (i) increased capsular polysaccharide synthesis (mucoid phenotype); (ii) increased synthesis of enzymes specified by at least four spatially separated operons involved in synthesis of capsular polysaccharide including the product of the galE gene, UDP-galactose-4-epimerase (EC 5.1.3.2) in capR mutants. The present study demonstrated that the entire galactose (gal) operon (galE, galT, and galK) is derepressed by mutations in either the capR or the capT genes, but not by mutation in capS. Double mutants (capR9 capT) were no more derepressed than the capR9 mutant, indicating that capR9 and capT regulate the gal operon via a common pathway. Isogenic double mutants containing either galR(+), galR(-), galR(s), or galO(c) in combination with either capR(+) or capR9 were prepared and analyzed for enzymes of the gal operon. The results demonstrated that capR9 caused derepression as compared to capR(+) in all of the combinations. Strains with a galR(s) mutation are not induced, for the gal operon, by any galactose compound including d-fucose, and this was confirmed in the present study using d-fucose. Nevertheless, the derepression of galR(s) capR9 compared to galR(s) capR(+) was four- to sixfold. The same derepression was observed when galR(+)capR9 was compared to galR(+)capR(+). The data eliminate the explanation that internal induction of the gal operon by a galactose derivative was causing increased gal operon enzyme synthesis in capR or capT mutants. Furthermore, the same data suggest that the galR and capR genes are acting independently to derepress the gal operon. A modified model for the structure of the gal operon is proposed to explain these results. The new feature of the model is that two operator sites are suggested, one to combine with the galR repressor and one to combine with the capR repressor.

Binding Sites↗
PubMed1976

Genetic co-regulation of galactose and melibiose utilization in Saccharomyces.

The gal3 mutation of Saccharomyces, which is associated with an impairment in the utilization of galactose, has been shown to be pleiotropic, causing similar impairments in the utilization of melibiose and maltose. Milibiose utilization and alpha-galactosidase production are directly controlled by the galactose regulatory elements i, c, and GAL4. The fermentation of maltose and the induction of alpha-glucosidase are regulated independently of the i, c, GAL4 system. The production of alpha-galactosidase and galactose-1-phosphate uridyl transferase is coordinate in galactokinaseless strains. Galactose serves as a nonmetabolized, gratuitous inducer of alpha-galactosidase in strains lacking the genes for one or more of the Leloir pathway enzymes.

Alleles↗
PubMed1989

Sequence and structure of the yeast galactose transporter.

The previously cloned GAL2 gene of the Saccharomyces cerevisiae galactose transporter has been sequenced. The nucleotide sequence predicts a protein with 574 amino acids (Mr, 63,789). Hydropathy plots suggest that there are 12 membrane-spanning segments. The galactose transporter shows both sequence and structural homology with a superfamily of sugar transporters which includes the human HepG2-erythrocyte and fetal muscle glucose transporters, the rat brain and liver glucose transporters, the Escherichia coli xylose and arabinose permeases, and the S. cerevisiae glucose, maltose, and galactose transporters. Sequence and structural motifs at the N-terminal and C-terminal regions of the proteins support the view that the genes of this superfamily arose by duplication of a common ancestral gene. In addition to the sequence homology and the presence of the 12 membrane-spanning segments, the members of the superfamily show characteristic lengths and distributions of the charged, hydrophilic connecting loops. There is indirect evidence that the transporter is an N-glycoprotein. However, its only N-glycosylation site occurs in a charged, hydrophilic segment. This could mean that this segment is part of a hydrophilic channel in the membrane. The transporter has a substrate site for the cyclic AMP-dependent protein kinase which may be a target of catabolite inactivation. The transporter lacks a strong sequence enriched for proline (P), glutamate (E), aspartate, serine (S), and threonine (T) and flanked by basic amino acids (PEST sequence) even though it has a short half-life. Mechanisms for converting the poor PEST to a possible PEST sequence are considered. Like the other members of the superfamily, the galactose transporter lacks a signal sequence.

Amino Acid Sequence↗
PubMed1994

Genetics of galactose metabolism of Erwinia amylovora and its influence on polysaccharide synthesis and virulence of the fire blight pathogen.

Galactose metabolism mutants of Erwinia amylovora were created by transposon insertions and characterized for their growth properties and interaction with plant tissue. The nucleotide sequence of the galE gene was determined. The gene, which encodes UDP-galactose 4-epimerase, shows homology to the galE genes of Escherichia coli, Neisseria gonorrhoeae, Rhizobium meliloti, and other gram-negative bacteria. Cloned DNA with the galE and with the galT and galK genes did not share borders, as judged by the lack of common fragments in hybridization with chromosomal DNA. These genes are thus located separately on the bacterial chromosome. In contrast to the gal operon of E. coli, the galE gene of E. amylovora is constitutively expressed, independently of the presence of galactose in the medium. The function of the galE gene but not of the galT or galK gene is required for bacterial virulence on pear fruits and seedlings. In the absence of galactose, the galE mutant was deficient in amylovoran synthesis. Subsequently, the galE mutant cells elicited host defense reactions, and they were not stained by fluorescein isothiocyanate-labelled lectin, which efficiently binds to amylovoran capsules of E. amylovora. The mutation affected the side chains of bacterial lipopolysaccharide, but an intact O antigen was not required for virulence. This was shown with another mutant, which could be complemented for virulence but not for side chain synthesis of lipopolysaccharide.

Amino Acid Sequence↗
PubMed1969

Effect of galactose on beta-galactosidase synthesis in Escherichia coli K-12.

In wild-type strains of Escherichia coli K-12, the rate of thiomethylgalactoside (TMG)-induced beta-galactosidase synthesis is decreased in the presence of galactose or glucose. A spontaneous mutant of a K-12 strain, 58-161, which synthesizes beta-galactosidase at a low rate was isolated. In this mutant, galactose, after a lag of about one generation time, evoked the same final differential rate of enzyme synthesis as did the gratuitous inducer TMG. However, constitutive, TMG-induced and galactose-induced synthesis in the mutant were subject to inhibition by exogenous glucose. It is concluded that repression of beta-galactosidase synthesis derived from glucose is distinct from the inhibition derived from galactose.

Enzyme Induction↗
PubMed2001

Biotyping of Penicillium marneffei reveals concentration-dependent growth inhibition by galactose.

Thirty-two isolates of the dimorphic fungus Penicillium marneffei were studied for their biochemical properties. All isolates possessed the enzyme urease and were inhibited by 500 mg of cycloheximide per liter. No strain fermented glucose, and thus no strain fermented any of the other five sugars tested. All assimilated glucose, maltose, and cellobiose; only one of the isolates did not assimilate salicin. Totals of 65.6, 84.4, and 71.9% of the isolates assimilated trehalose, xylose, and nitrate, respectively. Twelve strains possessed the enzyme beta-galactosidase. Overall, 17 different biotypes were recognized, but no association was found between the human immunodeficiency virus status of the patients and the biotype. A novel finding of concentration-dependent growth inhibition of P. marneffei by galactose is described. Inhibition of growth occurred at a low concentration of galactose (0.015 to 0.25%) when galactose was the sole carbon source in the medium. Morphological changes of the fungal cells were observed in the presence of galactose.

AIDS-Related Opportunistic Infections↗
PubMed1990

Transcription of a yeast phosphoglucomutase isozyme gene is galactose inducible and glucose repressible.

The Saccharomyces cerevisiae GAL5 (PGM2) gene was isolated and shown to encode the major isozyme of phosphoglucomutase. Northern (RNA) blot hybridization revealed that the GAL5 transcript level increased three- to fourfold in response to galactose and was severely repressed in response to glucose. Total cellular phosphoglucomutase activity was likewise responsive to galactose and to glucose, and this responsiveness was found to be due primarily to variation in the activity of the major isozyme of phosphoglucomutase. These results imply that the major and minor isozymes of phosphoglucomutase have distinct roles in yeast cells. The galactose inducibility of GAL5 was found to be under the control of the GAL4, GAL80, and GAL3 genes. In striking contrast to other galactose-inducible genes, the GAL5 gene exhibited an unusually high GAL4-independent basal level of expression. These results have implications for metabolic trafficking.

Cloning, Molecular↗
PubMed1996

Analysis of the galactose signal transduction pathway in Saccharomyces cerevisiae: interaction between Gal3p and Gal80p.

The GAL3 gene plays a critical role in galactose induction of the GAL genes that encode galactose- metabolizing enzymes in Saccharomyces cerevisiae. Defects in GAL3 result in a long delay in GAL gene induction, and overproduction of Gal3p causes constitutive expression of GAL. Here we demonstrate that concomitant overproduction of the negative regulator, Gal80p, and Gal3p suppresses this constitutive GAL expression. This interplay between Gal80p and Gal3p is direct, as tagged Gal3p coimmunoprecipitated with Gal80p. The amount of coprecipitated Gal80p increased when GAL80 yeast cells were grown in the presence of galactose. When both GAL80 and GAL3 were overexpressed, the amount of coprecipitated Gal80p was not affected by galactose. Tagged gal3 mutant proteins bound to purified Gal80p, but only poorly in comparison with the wild type, suggesting that formation of the Gal80p-Gal3p complex depends on the normal function of Gal3p. Gal3p appeared larger in Western blots (immunoblots) than predicted by the published nucleic acid sequence. Reexamination of the DNA sequence of GAL3 revealed several mistakes, including an extension at the 3' end of another predicted 97 amino acids.

Amino Acid Sequence↗
PubMed2004

High tolerance for oral galactose in classical galactosaemia: dietary implications.

AIM: To study the relevance of restricting the exogenous intake of small amounts of galactose, such as from fruit and vegetables, in patients with classical galactosaemia. METHODS: For a period of six weeks, increasing doses of oral galactose to a maximum of 600 mg per day, were added to a very strict galactose restricted diet in three adolescent patients homozygous for the Q188R mutation. During the study, physical examination, including an extended ophthalmic examination, and laboratory studies were performed on a weekly basis. RESULTS: No significant change in any of the studied clinical or biochemical parameters was observed. CONCLUSIONS: These findings provide further evidence that attempts to exclude trace amounts of galactose from the diet are not justified. Once the diet is made more liberal, a long term follow up study will be necessary.

Administration, Oral↗
PubMedDate not supplied

Simultaneous uptake of galactose and glucose by Azotobacter vinelandii.

Azotobacter vinelandii growing on galactosides induced two distinct permeases for glucose and galactose. The apparent Vmax and Km of the galactose permease were 16 nmol galactose/min per 10(10) cells and 0.5 mM, respectively. The apparent Vmax and Km of the glucose permease were 7.8 nmol glucose/min per 10(10) cells and 0.04 mM, respectively. Excess glucose had no effect on the galactose uptake. However, excess galactose inhibited glucose transport. The galactosides-induced glucose permease also exhibited different uptake kinetics from that induced by glucose.

Azotobacter vinelandii↗
PubMed2001

Characterization of oxidative stress in various tissues of diabetic and galactose-fed rats.

Rats fed a galactose-rich diet have been used for several years as a model for diabetes to study, particularly in the eye, the effects of excess blood hexoses. This study sought to determine the utility of galactosemia as a model for oxidative stress in extraocular tissues by examining biomarkers of oxidative stress in galactose-fed rats and experimentally-induced diabetic rats. Sprague-Dawley rats were divided into four groups: experimental control; streptozotocin-induced diabetic; insulin-treated diabetic; and galactose-fed. The rats were maintained on these regimens for 30 days, at which point the activities of catalase, glutathione peroxidase, glutathione reductase, and superoxide dismutase, as well as levels of lipid peroxidation and reduced and oxidized glutathione were determined in heart, liver, and kidney. This study indicates that while there are some similarities between galactosemic and diabetic rats in these measured indices of oxidative stress (hepatic catalase activity levels and hepatic and renal levels of oxidized glutathione in both diabetic and galactosemic rats were significantly decreased when compared to normal), overall the galactosemic rat model is not closely parallel to the diabetic rat model in extra-ocular tissues. In addition, several effects of diabetes (increased hepatic glutathione peroxidase activity, increased superoxide dismutase activity in kidney and heart, decreased renal and increased cardiac catalase activity) were not mimicked in galactosemic rats, and glutathione concentration in both liver and heart was affected in opposite ways in diabetic rats and galactose-fed rats. Insulin treatment reversed/prevented the activity changes in renal and cardiac superoxide dismutase, renal and cardiac catalase, and hepatic glutathione peroxidase as well as the hepatic changes in lipid peroxidation and reduced and oxidized glutathione, and the increase in cardiac glutathione. Thus, prudence should be exercised in the use of experimentally galactosemic rats as a model for diabetes until the correspondence of the models has been more fully characterized.

Administration, Oral↗
PubMed1987

Contribution of hepatic fatty acid oxidation and exogenous galactose supply to the regulation of glucose homeostasis in the newborn rabbit.

The inhibition of hepatic gluconeogenesis by 3-mercaptopicolinic acid (3-MPA) leads to a profound hypoglycemia in both suckling and fasting 24-hour-old rabbits. This hypoglycemia is totally reversed 1 h after the intragastric injection of an amount of galactose corresponding to the one ingested daily by the suckling newborns. This results from an active gluconeogenesis from galactose, which bypasses the site of inhibition by 3-MPA. However, this amount of galactose is not sufficient to maintain a normal blood glucose concentration for a long time, since 3 h after galactose injection, the blood glucose concentrations of newborn rabbits return to hypoglycemic values. When hepatic fatty acid oxidation is inhibited by 2-[6-(4-chlorophenoxy)hexyl]oxirane-2-carboxylate (POCA), 24-hour-old fasting rabbits become rapidly hypoglycemic secondary to a decrease in liver gluconeogenesis. The rate of hepatic gluconeogenesis is totally restored by giving medium-chain triglycerides, and the 24-hour-old rabbits become normoglycemic.

Animals↗
PubMed1972

Quantitative radioautography of sugar transport in intestinal biopsies from normal humans and a patient with glucose-galactose malabsorption.

Both galactose accumulation and phlorizin binding by columnar epithelial cells have been investigated in vitro with a recently developed technique for high-resolution, plastic-section radioautography which is particularly suited to small quantities of biopsy tissue. Grain density analysis of the radioautographs provides definitive support for the view that the cellular mechanisms underlying glucose-galactose absorption in laboratory animals are fully applicable to the small intestine of man. Even the number of sugar carriers at the microvillar membrane appears similar and the major quantitative difference, lower affinity for phlorizin in man, correlates with the finding that phlorizin is also a less potent inhibitor of uphill, galactose transport at the microvilli. In addition, radioautographs of biopsies taken 2 yr apart from a patient with glucose-galactose malabsorption provide evidence that the cellular defect in this inborn error of transport is a persistent reduction in the number of functioning sugar carriers at the microvillar membrane.

Adult↗
PubMed1985

Histochemical localization of galactose-containing glycoconjugate at peripheral nodes of Ranvier in the rat.

Lectin-horseradish peroxidase conjugates were used to study glycoconjugates in paraffin sections of dorsal roots of the rat spinal cord. Griffonia simplicifolia-B4 isolectin (GSA I-B4) and peanut agglutinin (PNA) stained strongly the nodes of Ranvier, localizing, respectively, terminal alpha- and beta-D-galactose. Sialidase digestion did not increase staining with PNA at the node of Ranvier, suggesting the presence of a neutral glycoconjugate. Staining of the nodal but not the internodal axolemma was observed with PNA. The outer surface of the myelin sheath in axons of the dorsal root stained strongly with GSA I-B4 but only weakly with PNA, demonstrating an abundance of terminal alpha-galactose. PNA staining was enhanced in this site by sialidase digestion, showing terminal sialic acid-beta-galactose dimers. The presence of sialic acid here was further evidenced by labeling of these membranes with the lectin derived from the slug, Limax flavus (LFA). Affinity for a high iron diamine-Alcian blue (pH 2.5) sequence demonstrated, in addition, the presence of sulfate esters in glycoconjugates on the outer myelin membrane. GSA I-B4 imparted strong reactivity to nonmyelinated fibers in the dorsal root and the spinal nerve. The present findings appear to reflect several localizations of biochemically described nervous system glycoproteins containing O-glycosidically linked side chains terminated by alpha- and beta-D-galactose.

Animals↗
PubMed1985

Histochemical localization of galactose-containing glycoconjugates in sensory neurons and their processes in the central and peripheral nervous system of the rat.

We studied the distribution of sugar residues in the oligosaccharide chains of complex carbohydrates in tissue sections of rat spinal cord, brainstem, and sensory ganglia using twelve lectin-horseradish peroxidase conjugates. Glycoconjugates containing terminal galactose residues were localized apparently in the Golgi apparatus in a population of predominantly small B-type neurons in spinal and trigeminal ganglia. Large A-type neurons rarely showed reactivity with galactose-binding lectins. A cells stained for glycoconjugates with N-glycosidically linked oligosaccharides and glycogen. The central and peripheral processes of the small neurons, mostly unmyelinated C fibers in sensory roots and spinal nerves, contained an abundance of glycoconjugates with terminal alpha-galactose residues. The central projections and terminals of small to medium-sized primary sensory neurons in the spinal and trigeminal ganglia were visualized in Lissauer's tract and the substantia gelatinosa in the spinal cord, and in the spinal trigeminal tract and the nucleus trigeminus in the lower medulla with lectins specific for terminal alpha-galactose residues. In addition, fibers of the solitary system and the area postrema were reactive with these lectins. The peripheral and central nervous system elements with affinity for galactopyranosyl-specific lectins correspond in distribution with neuroanatomical regions thought to be involved in the transmission and relay of somatic and visceral afferent inputs such as pain and temperature. Such specific localization of a glycosubstance to a distinct subpopulation of neurons and their peripheral and central processes suggests that the particular glycoconjugate may be of physiological significance.

Animals↗
PubMed1994

The effect of glucose and galactose toxicity on myo-inositol transport and metabolism in human skin fibroblasts in culture.

Myo-inositol transport and metabolism were studied in cultured human skin fibroblasts exposed to potentially toxic levels of glucose or galactose. Although variable among 11 different cell lines, the myo-inositol level in confluent cells, ranging from 10-50 nmol/mg protein, was constant with passage. A high-affinity transport system for myo-inositol had an apparent Kt of 55 microM and Vmax of 16 pmol/min/mg protein. No obvious relationship existed between cellular levels and transport capacity. Dependency on sodium was complex. When medium sodium was lowered to 23 mM, myo-inositol uptake ceased after about 1 h. However, the initial rate of myo-inositol uptake only showed a sodium dependence at low myo-inositol concentrations. Both phloretin and phloridzin inhibited myo-inositol uptake. Phloridzin had a Ki of 60 microM, and phloretin was either a noncompetitive or uncompetitive inhibitor. Glucose and galactose were only weak competitive inhibitors, with a Ki of 30 mM and 65 mM, respectively. After 24 h of incubation with myo-[2-3H]inositol, only 10% of the total cell label was incorporated into phospholipid. Compared with control media with 5 mM glucose, the incubation of confluent cells in media with 20 mM glucose had little effect on intracellular glucose and sorbitol, whereas cells incubated in control media supplemented with 5 mM galactose showed a large increase in galactose and polyol levels. In media with more than 200 microM of myo-inositol, neither treatment had an effect on myo-inositol levels after 24 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Biological Transport, Active↗
PubMed1994

Glucose, galactose, and glutamine metabolism in pig isolated enterocytes during development.

In the pig, the gastrointestinal tract grows rapidly after birth and undergoes a short postnatal maturation. The objective of the present work was to assess the metabolic characteristics of the small intestinal mucosa during this period by investigating glucose, galactose, and glutamine metabolism in pig isolated enterocytes. Piglets were used immediately after birth or at various stages during suckling or postweaning. Fed animals were taken in a postabsorptive state. The jejunoileum was excised and perfused with an EDTA (5 mM)-containing buffer. The epithelial cell layer was further dissociated in the presence of hyaluronidase (0.01%). The resulting cell suspension (95% absorbing enterocytes; viability greater than 90%) was incubated with 14C-labeled substrates to measure 14CO2 production in parallel with substrate disappearance. The capacity to utilize glutamine was high and remained steady during the suckling period. Glucose utilization capacity was limited at birth and increased more than 3-fold during the first week of suckling. Such an increase was not observed in piglets kept unsuckled since birth. Galactose utilization capacity remained steady during the first week but afterward gradually disappeared. Lactate and pyruvate production through glycolysis was the major pathway accounting for glucose or galactose disappearance. A capacity for a net glucose production from galactose was evidenced during the first week of suckling. Thus, isolated newborn pig enterocytes exhibit specific and transient metabolic characteristics during the first postnatal week.

Animals↗
PubMed1990

Effects of novel hydantoin derivatives with aldose reductase inhibiting activity on galactose-induced cataract in rats.

Effects of novel aldose reductase inhibitors, M16209 (1-(3-bromobenzo[b]furan-2-ylsulfonyl)hydantoin) and M16287 (1-(3-chlorobenzo[b]furan-2-ylsulfonyl)hydantoin), on galactose-induced cataract formation in rats were investigated. Rats fed a 30% galactose diet developed lenticular opacity in the peripheral region by the 6th day of galactose feeding and showed gradual progression of opacity from the equator to the center of lenses. Histological study on the 15th day showed apparent lens fiber swelling and vacuolation predominantly in the equatorial and anterior cortical regions. Biochemical changes such as accumulation of galactitol, depletion of myo-inositol and decrease in glutathione (GSH) content in lenses preceded the appearance of opacity. Remarkable increase in NADPH content and decrease in NADP+ content, in addition to elevation of the ratio of Na+/K+, in lenses were also observed on the 15th day. Both M16209 and M16287 (10, 30 and 100 mg/kg/day, p.o.) dose-dependently ameliorated these morphological and biochemical changes except that restoration of myo-inositol content was incomplete. These results indicate that M16209 and M16287 can prevent galactose-induced cataract formation through amelioration of metabolic disorders and thus have high potential for clinical use in the treatment of some diabetic complications.

Aldehyde Reductase↗