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PubMed1971

Galactose transport across the hamster small intestine: the effect of sodium electrochemical potential gradients.

1. Measurements of galactose unidirectional fluxes across the isolated mucosa of the hamster small intestine were made under a variety of experimental conditions designed to investigate the interrelationships between galactose transport, the sodium ion and electrical potentials.2. Galactose transport was inhibited by lowering the sodium concentration in the mucosal and/or serosal solutions and by increasing the p.d. across the tissue. This inhibition of galactose transport was judged to be irreversible.3. Transport was unaffected by decreasing the p.d. across the tissue.4. These results are discussed in relation to the model proposed to explain galactose transport across the intestine.

Animals↗
PubMed1991

Postprandial blood concentrations of insulin-independent carbohydrate, galactose, in oral test after gastric surgery.

In order to examine the postprandial blood concentrations of insulin-independent carbohydrates after gastric surgery oral galactose test (1.65 g/kg body weight in water, 33%, w/v) was performed in 55 symptomatic patients and in 5 healthy subjects. There were patients after total gastrectomy (TG) (n = 17), gastric resection with (GRS, n = 17) or without (GR; n = 12) selective vagotomy, and after proximal selective vagotomy (PSV, n = 9). The patients had immediately after drinking the test solution a 2- to 5-fold higher blood galactose concentration than the healthy subjects. The TG patients had the most rapid, the healthy subjects the slowest and the GR and GRS patients an intermediate rapid, immediate increase of blood galactose concentration. The TG patients showed a plateau 40-60 min and a decrease 60-90 min after the start of the test. The PSV patients showed a plateau 60-90 min after the commencement of the test. The GR and GRS patients and the healthy subjects had a continuous increase in blood galactose concentration during the whole test period, but the maximal point 90 min after the drinking of the solution was lower in the GRS than in the GR patients and lowest in the healthy subjects. The PSV patients had a lower blood galactose curve than the TG, GRS and GR patients but higher than the healthy subjects except the plateau 60-90 min postprandially.(ABSTRACT TRUNCATED AT 250 WORDS)

Carbohydrate Metabolism↗
PubMed1975

Developmental aspects of galactose-1-phosphate uridylytransferase in rat intestine.

Kinetic and developmental characteristics of rat jejunal galactose-1-phosphate uridylyltransferase have been examined. Km values for the substrates galactose-1-phosphate and uridine diphosphate (UDP) glucose were the same for both the newborn and adult rat enzymes, although the Vmax of the enzyme in newborns was about threefold higher than that of the adult rat. Equal enzyme activity was present in the villus, crypt cells and the muscularis of adult jejunum. The specific activity of the enzyme remained relatively uniform (V about 20 nmoles/min/mg protein) until 18 days of age when the velocity of the reaction began to decrease. The adult value at 42 days of age is about one fifth of that in the young. The pattern of change of specific activity was compared with that for galactokinase and UDP-galactose-4-epimerase, and the observations suggest separated regulatory factors for each enzyme. The total activity of the galactose-metabolizing enzymes in jejunum was also calculated. In the young, transferase has the highest activity, but in the adult, epimerase activity is highest. Jejunal galactokinase activity is low throughout the developmental period which suggests that phosphorylation of galactose may be the limiting step in intestinal metabolism of the sugar.

Animals↗
PubMed1985

Utilization of galactose by human platelets in vitro.

The extent to which platelets can metabolize galactose has been unknown. We have studied this question by incubating platelets with radiolabeled galactose for periods of time and analyzing the cells for radioactive metabolites. The sugar was observed to accumulate quickly in cells isolated by filtration. Within seconds at room temperature, galactose metabolites were detectable by thin-layer chromatography, and within 20 minutes at 37 degrees C, radioactivity appeared in trichloroacetic acid (TCA) precipitates of the suspensions. The TCA-precipitable radioactivity was degraded by alpha-amylase as well as by protease. However, the TCA-soluble material released by protease digestion had an elution volume on Sepharose CL-4B too small for glycopeptides and in addition was degraded by alpha-amylase. The majority of the galactose metabolized by platelets, therefore, becomes incorporated into glycogen, rather than glycoprotein. The reversibility of the galactose metabolic pathway was demonstrated by the addition of an excess of the unlabeled sugar to the labeled platelets and by the effect of thrombin and collagen on the TCA-precipitable radioactivity.

Blood Platelets↗
PubMed1977

Uridine diphosphate galactose 4'-epimerase deficiency. IV. Report of eight cases in three families.

Eight persons who had no activity of uridine diphosphate galactose 4'-epimerase in their circulating blood cells are known today. They were healthy members of three different families. Propositi were newborns discovered in a mass screening test for blood galactose which registered high levels of erythrocyte galactose-1-phosphate. Epimerase deficiency was restricted to circulating blood cells, but in liver biopsy specimens, in cultured skin fibroblasts and in activated lymphocytes epimerase was found to be normally active. Heterozygotes had intermediate red cell epimerase activity. There were no symptoms of galactose intolerance and no pathology related to the enzyme defect. All 8 epimerase deficient persons had a ccdee Rhesus genotype. Attempts at demonstrating genetic linkage between the epimerase and Rhesus loci were unsuccessful because of the difficulty encountered in ascertaining epimerase heterozygosity. Individuals with hereditary UDP-galactose 4'-epimerase deficiency appear to produce an unstable mutant enzyme requiring higher NAD concentration for maximum activity.

Aged↗
PubMed1976

Uridine 5'-diphosphate-galactose:glycoprotein galactosyltransferase activity in the ovarian cancer patient.

Uridine 5'-diphosphate-galactose:glycoprotein galactosyltransferase activity was demonstrated in homogenates of normal ovary and ovarian epithelial adenocarcinomas. The specific activity of the enzyme in ovarian tumors was 3 to 5 times higher than in normal ovaries when the enzyme was assayed under identical conditions. The glycoprotein fetuin, from which terminal sialic acid and penultimate galactose were removed (fetuin minus N-acetylneuraminis acid and galactose), acted as an excellent exogenous acceptor. Galactosyltransferase from normal ovary and ovarian tumor cells had similar properties. Both required Mn2+ and Triton X-100 and had broad pH optima between 5.5 and 7. Galactosyltransferase activity was also measured in serum samples from ovarian cancer patients and normal healthy individuals in the presence of fetuin minus N-acetylneuraminic acid and galactose as exogenous acceptor. The enzyme levels were significantly elevated in the sera of ovarian cancer patients as compared to normal controls. The differences in the levels of this enzyme in the tissues and sera of normal individuals and ovarian cancer patients were not due to differential levels of the degrading enzymes such as uridine 5'-diphosphate-galactose pyrophosphatase or beta-D-galactosidase. Serial determinations were carried out on the sera of 5 ovarian cancer patients over a long period of time. The serum level of galactosyltransferase activity appeared to correlate with tumor volume as well as with the clinical status of the patient, which suggests possible leakage of the tumor enzyme into the host sera. Serial determination of this enzyme level in ovarian cancer patients seems promising in measuring tumor progression or success of therapeutic approaches.

Adenocarcinoma↗
PubMed1976

Galactosemia with endogenous production of galactose-1-phosphate and with cystic fibrosis-like appearance at autopsy.

In an infant with galactosemia high levels of galactose-1-phosphate in red blood cells and of blood galactose were observed under a "galactose-free'' diet. The child did not thrive and developed a liver cirrhosis. At the age of 5 months he died unexpectedly. Post mortem examination revealed in the pancreas and the small intestine changes suggestive of a cystic fibrosis. Since the exogenous administration of galactose by diet could be excluded the endogenous production of significant amounts of galactose-1-phosphate has to be considered.

Autopsy↗
PubMed1977

An enzyme-P.M.R.-spectroscopic determination of the enantiomers of galactose.

The action of D-galactose oxidase on D-galactose in the presence of oxygen afforded meso-galacto-hexodialdose quantitatively, which allowed p.m.r.-spectroscopic determination of the D enantiomer in a DL mixture. In the spectrum of the products obtained from the enzymic treatment of a mixture of D- and L-galactose, the magnitude of the aldehydrol signals derived solely from the oxidised D enantiomer, relative to those of the anomeric signals, provided the fractional content of the D enantiomer. This simple, accurate, and convenient procedure was applied to the hydrolysate of a seaweed galactan, which was also analyzed, for comparative purposes, by the fermentation technique employing D-galactose-adapted Saccharomyces cerevisiae.

Galactose↗
PubMedDate not supplied

Galactose-containing amphiphiles prepared with a lipophilic radical initiator: association processes between liposomes triggered by enzymatic reaction.

A galactose-containing monomer (2-(methacryloyloxy)ethyl beta-D-galactopyranoside, MEGal) was polymerized by using a lipophilic radical initiator. The amphiphile obtained formed a liposome by mixing with bis(trans,trans-2,4-dioctadecadienoyl)phosphatidylcholine (DDPC), and the liposome obtained was physically stabilized by the polymerization of DDPC by UV irradiation. The enzymatic treatment of the galactose-containing liposomes with galactose oxidase resulted in the formation of aldehyde groups on the liposome surface. By the subsequent mixing of the liposome suspension with the amino group-containing liposome suspension, a rapid increase in turbidity was observed due to the formation of Schiff bases between the aldehyde groups and the amino groups at the interface of the liposomes. The rate of turbidity change strongly depended on the degree of polymerization of MEGal, the surface densities of galactose and amino groups on the liposome, the distance from the liposome surface to amino end groups, and the flexibility and deformability of the liposomes.

1,2-Dipalmitoylphosphatidylcholine↗
PubMed1998

UDP-galactose:ceramide galactosyltransferase is a class I integral membrane protein of the endoplasmic reticulum.

UDP-galactose:ceramide galactosyltransferase (CGalT) transfers UDP-galactose to ceramide to form the glycosphingolipid galactosylceramide. Galactosylceramide is the major constituent of myelin and is also highly enriched in many epithelial cells, where it is thought to play an important role in lipid and protein sorting. Although the biochemical pathways of glycosphingolipid biosynthesis are relatively well understood, the localization of the enzymes involved in these processes has remained controversial. We here have raised antibodies against CGalT and shown by immunocytochemistry on ultrathin cryosections that the enzyme is localized to the endoplasmic reticulum and nuclear envelope but not to the Golgi apparatus or the plasma membrane. In pulse-chase experiments, we have observed that newly synthesized CGalT remains sensitive to endoglycosidase H, confirming the results of the morphological localization experiments. In protease protection assays, we show that the largest part of the protein, including the amino terminus, is oriented toward the lumen of the endoplasmic reticulum. CGalT enzyme activity required import of UDP-galactose into the lumen of the endoplasmic reticulum by a UDP-galactose translocator that is present in the Golgi apparatus of CHO cells but absent in CHOlec8 cells. Finally, we show that CGalT activity previously observed in Golgi membrane fractions in vitro, in the absence of UDP-glucose, is caused by UDP-glucose:ceramide glucosyltransferase. Therefore all galactosylceramide synthesis occurs by CGalT in vivo in the lumen of the endoplasmic reticulum.

Animals↗
PubMed1963

GALACTOSE METABOLISM BY RAT LIVER TISSUE: INFLUENCE OF AGE.

The metabolism of galactose by liver tissue from fetal, new-born, pre-adult, and adult rats was studied in vitro by determining the extent of conversion of galactose to CO(2) and the disappearance of the sugar from the incubation medium. Results indicate that the utilization of galactose by liver tissue decreases as the organism grows older. The explanation of the tendency of patients with congenital galactosemia to improve symptomatically with age on the basis of "maturation" of galactose metabolizing pathways in their livers does not appear to be consistent with these observations.

Aging↗
PubMed1992

Abnormal galactosylation of complex carbohydrates in cultured fibroblasts from patients with galactose-1-phosphate uridyltransferase deficiency.

An abnormality in galactosylation of complex carbohydrates may be important in the pathogenesis of the long-term complications of classic (galactose-1-phosphate uridyltransferase-deficient) galactosemia. The ability of nine galactosemic fibroblast preparations to be galactosylated with a purified galactosyltransferase was measured as an indicator of vacant sites where galactose would normally reside. The amount of galactose transferred to cell protein from galactosemic patients was significantly higher than that transferred to a group of seven controls (p less than 0.005). Galactosyltransferase activity of the galactosemic cell preparation toward N-acetylglucosamine was also significantly higher than normal (p less than 0.01), and there was a linear relationship between these two parameters in galactosemic but not normal cells. These findings suggest that there is defective galactosylation of galactosemic cell complex carbohydrates and that such cells increase their galactosyltransferase levels in an attempt to compensate for the defect. Defective galactosylation may be implicated as an etiologic factor in complications observed in galactosemic patients even when treated with galactose-restricted diets.

Carbohydrate Metabolism↗
PubMed1983

[Intravenous loading with galactose as a liver function test. Methods and clinical value].

The determination of the galactose elimination capacity with the method according to Tygstrup (1966) is the only test which detects the "functional hepatocyte mass" and thus constitutes a quantitative test for the metabolic function of the liver. In this determination of the maximum hepatic elimination capacity, differences with bilirubin, hemolysis and hyperlipidemia do not occur; reliable results are also obtained in disorders of hepatic secretion. Side-effects from the test substance galactose are not to be expected. It is also possible to determine galactose without difficulty in capillary blood. The i.v. galactose test permits an estimation of the degree of severity of liver diseases and can also be recommended for routine use in the investigation of specific hepatological questions.

Galactose↗
PubMed1980

Evaluation of an immobilized-enzyme analyzer for measuring galactose in serum.

Reportedly, galactose provides an alternative carbohydrate source and improved homeostatic regulation of glucose in the premature infant. Because of its potentially toxic effects, sensitive methods are needed for monitoring its concentration during therapy. We evaluated an immobilized galactose oxidase/hydrogen peroxide electrode system and a modified homogeneous enzymic method. Both methods are suitable for measuring galactose in a small sample and are comparably precise. The latter method gives superior analytical recoveries below 100 mg/L, but is linear in absorbance response to only 300 mg/L. We find the immobilized-enzyme method superior for monitoring treatment of neonates with galactose, because it requires only a few minutes and 25 microL of serum, and the analytical procedure is simpler.

Enzymes, Immobilized↗
PubMed1998

Retinal vessel changes in galactose-fed dogs.

BACKGROUND: Retinal lesions similar to those in human early-stage diabetic retinopathy have been reported to occur in dogs fed galactose for long periods. Investigations of retinal changes, however, have been limited to studies of the intact retinal vasculature isolated by trypsin digestion. OBJECTIVE: To document the onset and progression of retinal lesions in galactose-fed dogs by the common clinical techniques of fundus color photography and fluorescein angiography. METHODS: Fourteen 6-month-old male beagles made aphakic in 1 eye were divided into a control group (4 dogs), receiving a diet containing 30% cellulose, and a galactosemic group (10 dogs), receiving a diet containing 30% galactose. The progression of retinal changes in these dogs was periodically monitored by color fundus photography and fluorescein angiography. RESULTS: Dogs fed a 30% galactose diet for 28 to 41 months were observed by fluorescein angiography and color fundus photography to develop, in order of frequency, microaneurysms, retinal hemorrhages, intraretinal microvascular abnormalities, retinal nonperfused areas, and varicose and serpiginous veins. These findings are similar to the early clinical retinal changes observed in humans with diabetes. CONCLUSION: These results confirm that galactosemic dogs are an appropriate and suitable animal model for investigating human diabetic retinopathy.

Animals↗
PubMed1992

Diabeteslike preproliferative retinal changes in galactose-fed dogs.

Retinal vessel changes were experimentally investigated by a combination of color fundus photography, fluorescein angiography, and histologic studies in beagles that were fed a 30% galactose diet for up to 66 months. Previously, we have described the appearance of pericyte ghosts, microaneurysms, acellular capillaries, and intraretinal hemorrhages in dogs fed a galactose diet for up to 36 months. These disorders were similar to those observed in humans with background diabetic retinopathy. We report herein that dogs fed galactose for 48 to 60 months experience retinal changes associated with the chronic occlusion of capillary beds and subsequent ischemia of the retina. These changes included the appearance of broad areas of nonperfusion, soft exudates (cytoid bodies), intraretinal microvascular abnormalities, occluded arterioles, preretinal and intravitreal hemorrhages, and apparent new vessel growth around the optic disc. The present study clearly demonstrates that the galactose-fed dog is an animal model in which advanced retinal changes develop, and these changes are similar to those associated with preproliferative human diabetic retinopathy.

Animals↗
PubMed1997

Galactose-inducible expression systems in Candida maltosa using promoters of newly-isolated GAL1 and GAL10 genes.

The GAL1 and GAL10 gene cluster encoding the enzymes of galactose utilization was isolated from an asporogenic yeast, Candida maltosa. The structure of the gene cluster in which both genes were divergently transcribed from the central promoter region resembled those of some other yeasts. The expression of both genes was strongly induced by galactose and repressed by glucose in the medium. Galactose-inducible expression vectors in C. maltosa were constructed on low- and high-copy number plasmids using the promoter regions of both genes. With these vectors and the beta-galactosidase gene from Kluyveromyces lactis as a reporter, galactose-inducible expression was confirmed. Homologous overexpression of members of the cytochrome P-450 gene family in C. maltosa was also successful by using a high-copy-number vector under the control of these promoters.

Amino Acid Sequence↗
PubMed2003

High density of immobilized galactose ligand enhances hepatocyte attachment and function.

Galactosylated surface is an attractive substrate for hepatocyte culture because of the specific interaction between the galactose ligand and the asialoglycoprotein receptor on hepatocytes. In this study, we described a scheme to achieve high density of immobilized galactose ligands on polyethylene terephthalate (PET) surface by first surface-grafting polyacrylic acid on plasma-pretreated PET film under UV irradiation, followed by conjugation of a galactose derivative (1-O-(6'-aminohexyl)-D-galactopyranoside) to the grafted polyacrylic acid chains. A high galactose density of 513 nmol/cm(2) on the PET surface was used in this study to investigate the behavior of cultured hepatocyte. This engineered substrate showed high affinity to fluorescein isothiocyanate-lectin binding. Primary rat hepatocytes, when seeded at a density of 2 x 10(5) cells/cm(2), attached to the galactosylated PET substrate at a similar efficiency compared with collagen-coated substrate. The hepatocytes spontaneously formed aggregates 1 day after cell seeding and showed better maintenance of albumin secretion and urea synthesis functions than those cultured on collagen-coated surface.

Acrylic Resins↗