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PubMed1997

Liver and lens glutathione and cysteine regulation in galactose-fed guinea pigs.

PURPOSE: To study the mechanism of lenticular glutathione (GSH) depletion in galactose-fed guinea pigs, with particular reference to correlations between liver and lens GSH, precursor (cysteine) status and GSH synthetic capacities. METHODS: Guinea pigs in the ad libitum-fed state were fed powdered guinea pig chow containing 50% galactose for 3 and 14-16 days. Plasma GSH and GSH levels in lens, liver and freshly isolated hepatocytes were determined. Maximal rates of GSH synthesis in liver and lens as well as steady state levels of precursor cysteine were also determined. In separate experiments, linear rate of 35S-cysteine uptake was studied in isolated hepatocytes from control and galactose-fed animals. Lens and liver GSH decreased significantly with galactose feeding. Hepatic GSH showed a dramatic decrease (approximately 83%) as early as day 3 whereas approximately 43% decrease was observed in lens. The maximal GSH synthetic rates (GSH-SR) in the whole lens and liver on days 3 and 14-16 were not different from those of controls. Steady-state levels of cysteine also decreased in both tissues with galactose feeding, and the magnitude of decrease was higher in the liver as compared to the lens. The rate of cysteine uptake in hepatocytes isolated from galactose-fed guinea pigs was significantly lower for the cysteine concentrations studied (10 microM to 1 mM) as compared to control uptake. The decreased steady-state liver GSH and cysteine levels in galactose-fed guinea pigs caused a significant decrease in plasma (and aqueous) GSH concentrations. CONCLUSIONS: We concluded that the decrease in lens GSH due to galactose occurs without alterations in the capacity of GSH synthesis, in either lens or liver. It is suggested that decreased hepatic GSH, resulting in reduced plasma GSH levels due to decreased GSH efflux into plasma, may contribute to impairment in plasma to lens GSH transport with galactose. Thus, the functional role of recently identified lens GSH transporters, particularly that of Na(+)-dependent GSH transporter, in galactose-induced cataract formation will be worthy of investigation.

Animals↗
PubMed1990

Comparison of the effects of dietary glucose versus galactose on porcine feto-placental glucose metabolism.

The present study was conducted to determine whether dietary galactose can be used to improve glycogen and lipid accretion in fetal pigs. Pregnant gilts were fed diets containing either 24% glucose (control) or 24% galactose from d 98 to 110 of gestation. Gilts underwent abdominohysterotomy on d 110 of gestation. Slices of fetal subcutaneous adipose tissue and placenta were examined for metabolic capacity for glucose and for galactose utilization. No effects of maternal diet were evident upon glycogen content or enzyme activity of fetal semitendinosus muscle and liver. Maternal dietary galactose had no direct effects upon placental glucose oxidation or use for lipid synthesis. However, galactose supplementation of the incubation medium caused reductions in glucose oxidation (15%) and total lipid synthesis (24%) by the maternal placenta. Maternal dietary galactose caused an increase in total lipid (50%) and fatty acid synthesis (200%) from glucose in fetal subcutaneous adipose tissue; direct supplementation of galactose to the incubation medium had no effect on these parameters. The results of the present study suggest that feeding galactose to the pregnant gilt does not have direct effects upon placental metabolism or fetal glycogen storage. However, these data indicate that use of galactose in the maternal diet can result in an increase in the utilization of glucose for lipogenesis by fetal adipose tissue in swine. This effect is not a direct effect of galactose because transport across the placenta was not apparent.

Adipose Tissue↗
PubMed1993

Schwann cell injury is attenuated by aldose reductase inhibition in galactose intoxication.

Four months of galactose intoxication induces a dose-dependent osmotic imbalance of the nerve microenvironment characterized by polyol, water, and electrolyte accumulation. Recently, dose-dependent cellular lesions have been described in the sciatic nerves of galactose-intoxicated rats. The present study was designed to demonstrate that the cell injury and endoneurial osmotic imbalance in galactose intoxication are dependent on the subsequent metabolism of galactose by the polyol pathway. Three groups of age-matched, female Sprague-Dawley rats were fed a control diet or diets containing complete micronutrient supplements with 40% galactose or 40% galactose and 0.04% Ponalrestat, an aldose reductase inhibitor (ARI). After 4 to 5 months, sciatic nerves were analyzed for polyol, water and endoneurial electrolyte content and processed for light and electron microscopic examination. Ponalrestat prevented myo-inositol depletion and accumulations of dulcitol, water and endoneurial fluid electrolytes. Axonal size-frequency histograms revealed that Ponalrestat attenuated the shift toward smaller fibers and the decrease in mean axonal diameter seen in untreated galactose-fed rats. Electron microscopic examination showed widespread reactive and degenerative changes in Schwann cells of galactose-intoxicated rats that culminated in cytoplasmic disintegration. Quantitative electron microscopy revealed that ARI treatment significantly reduced the incidence of abnormal Schwann cells. These observations indicate that the osmotic imbalance and cell injury seen in galactose intoxication are dependent on the metabolism of galactose by the polyol pathway.

Aldehyde Reductase↗
PubMed1979

Control of the receptor for galactose taxis in Salmonella typhimurium.

The chemotactic response to galactose in wild-type Salmonella typhimurium is not inducible by galactose, but is inducible by fucose, a non-metabolizable analog. In a galactokinase mutant, however, the galactose receptor is inducible by galactose. These data indicate that the concentration of free galactose in the cell controls the levels of the galactose receptor. The intensities of the chemotactic responses were found to vary in proportion to the concentration of galactose receptors. In bacteria with higher levels of galactose receptors, the ribose response is inhibited by galactose. This supports the model in which the ribose and galactose receptors compete for a common component of the signaling system.

Chemotaxis↗
PubMed1992

Overproduction of the GAL1 or GAL3 protein causes galactose-independent activation of the GAL4 protein: evidence for a new model of induction for the yeast GAL/MEL regulon.

The transcriptional activation function of the Saccharomyces cerevisiae GAL4 protein is modulated by the GAL80 and GAL3 proteins. In the absence of galactose, GAL80 inhibits the function of GAL4, presumably by direct binding to the GAL4 protein. The presence of galactose triggers the relief of the GAL80 block. The key to this relief is the GAL3 protein. How GAL3 and galactose activate GAL4 is not understood, but the long-standing notion has been that a galactose derivative formed by catalytic activity of GAL3 is the inducer that interacts with GAL80 or the GAL80-GAL4 complex. Here we report that overproduction of the GAL3 protein causes constitutive expression of GAL/MEL genes in the absence of exogenous galactose. Overproduction of the GAL1 protein (galactokinase) also causes constitutivity, consistent with the observations that GAL1 is strikingly similar in amino acid sequence to GAL3 and has GAL3-like induction activity. Cells lacking the GAL10-encoded UDP-galactose-UDP-glucose epimerase retained the constitutivity response to overproduction of GAL3, making it unlikely that constitutivity is due to endogenously produced galactose. A galactose-independent mechanism of constitutivity is further indicated by the inducing properties of two newly created galactokinaseless alleles of GAL1. On the basis of these data, we propose a new model for galactose-induced activation of the GAL4 protein. This model invokes galactose-activation of the GAL3 and GAL1 proteins which in turn elicit an alteration of the GAL80-GAL4 complex to activate GAL4. This model is consistent with all the known features of the system and has important implications for manipulating GAL4-dependent transcriptional activation in vitro.

DNA-Binding Proteins↗
PubMed1989

Effect of galactose and glucose levels and sorbinil treatment on myo-inositol metabolism and Na+-K+ pump activity in cultured neuroblastoma cells.

Neuroblastoma cells were used to analyze the effect of galactose supplementation on myo-inositol metabolism, polyol accumulation, and Na+-K+ pump activity. Culturing cells in 30 mM galactose for a minimum of 1 wk led to a large accumulation of intracellular galactitol and a greater than 50% decrease in myo-inositol content. The effect of galactose on the intracellular content of galactitol and myo-inositol was concentration dependent. Extracellular myo-inositol accumulation and incorporation into phospholipid decreased by 20-30% in cells grown in 30 mM galactose. The decrease in myo-inositol accumulation is apparently due to a noncompetitive inhibition of high-affinity myo-inositol uptake. Treatment of the galactose-containing media with 0.4 mM sorbinil partially prevented the galactose-mediated decreases in myo-inositol metabolism and content. The galactitol content of the sorbinil-treated cells was significantly reduced compared with the galactitol levels in cells cultured in 30 mM galactose; however, galactitol levels remained significantly elevated over control cells. Exposing neuroblastoma cells to 30 mM galactose causes a decrease in the levels of phosphatidylinositol that is partially restored by the addition of sorbinil. The activity of the Na+-K+ pump was decreased by 20% in cells cultured in 30 mM galactose and was partially protected by sorbinil treatment. The effects of long-term galactose supplementation on myo-inositol metabolism, polyol accumulation, and Na+-K+-ATPase transport activity in cultured neuroblastoma cells are similar to the effects of high concentrations of glucose. These results provide additional evidence that the accumulation of polyol by neuroblastoma cells is partially responsible for alterations in myo-inositol metabolism and decreases in Na+-K+-ATPase transport activity.

Aldehyde Reductase↗
PubMed1997

Aldose reductase inhibition increases CNTF-like bioactivity and protein in sciatic nerves from galactose-fed and normal rats.

The impact of exaggerated polyol pathway flux on ciliary neurotrophic factor (CNTF)-like bioactivity and expression of CNTF in rat sciatic nerve was examined after 2 months of galactose intoxication. Polyol content was elevated (P < 0.001) and motor nerve conduction velocity reduced (P < 0.05) in galactose-fed rats compared with control animals or control and galactose-fed rats treated with the aldose reductase inhibitor (ARI) Ponalrestat. CNTF-like bioactivity in the galactose-fed group was reduced to 30% of that assayed in the control group (P < 0.001). ARI treatment significantly increased CNTF-like bioactivity by 60% compared with the untreated galactose group (P < 0.05) but did not restore it to control levels. Unexpectedly, bioactivity in ARI-treated control animals was increased by nearly 250% compared with untreated controls (P < 0.005). In addition to the deficit in CNTF bioactivity in untreated galactose rats, the expression of protein, but not of mRNA, was reduced (P < 0.05). In ARI-treated control and galactose-fed rats, the expression of CNTF peptide was significantly enhanced above control levels (both P < 0.05). Concomitant with the reduction in CNTF levels, there was a shift in the axonal size-frequency distribution of myelinated fibers toward smaller axons in galactose-fed rats that was prevented by ARI treatment. Since galactose feeding has little impact on levels of CNTF mRNA, these observations suggest that deficits in CNTF-like bioactivity may result from a posttranscriptional modification of neurotrophic protein expression or turnover. Unlike other functional and structural disorders in galactose neuropathy, factors other than polyol accumulation may contribute to the deficit in CNTF-like bioactivity.

Aldehyde Reductase↗
PubMed1999

Coexpression of alpha1,2 galactosyltransferase and UDP-galactose transporter efficiently galactosylates N- and O-glycans in Saccharomyces cerevisiae.

We have studied in vivo neo-galactosylation in Saccharomyces cerevisiae and analyzed the critical factors involved in this system. Two heterologous genes, gma12(+) encoding alpha1, 2-galactosyltransferase (alpha1,2 GalT) from Schizosaccharomyces pombe and UGT2 encoding UDP-galactose (UDP-Gal) transporter from human, were functionally expressed to examine the intracellular conditions required for galactosylation. Detection by fluorescence labeled alpha-galactose specific lectin revealed that 50% of the cells incorporated galactose to cell surface mannoproteins only when the gma12(+) and hUGT2 genes were coexpressed in galactose media. Integration of both genes in the Delta mnn1 background cells increased galactosylation to 80% of the cells. Correlation between cell surface galactosylation and UDP-galactose transport activity indicated that an exogenous supply of UDP-Gal transporter rather than alpha1,2 GalT played a key role for efficient galactosylation in S.cerevisiae. In addition, this heterologous system enabled us to study the in vivo function of S. pombe alpha1,2 GalT to prove that it transfers galactose to both N - and O -linked oligosaccharides. Structural analysis indicated that this enzyme transfers galactose to O -mannosyl residue attached to polypeptides and produces Galalpha1,2-Man1-O-Ser/Thr structure. Thus, we have successfully generated a system for efficient galactose incorporation which is originally absent in S. cerevisiae, suggesting further possibilities for in vivo glycan remodeling toward therapeutically useful galactose containing heterologous proteins in S. cerevisiae.

Biological Transport↗
PubMed1982

A new microfluorometric method for the measurement of galactose-1-phosphate in erythrocytes.

A new and sensitive assay for measuring galactose-1-phosphate in erythrocytes is described. Galactose-1-phosphate is determined by mixing an aliquot of deproteinized hemolysate with a reagent containing uridine diphosphoglucose, NADP+, hexose-1-phosphate uridylyltransferase, phosphoglucomutase, glucose-6-phosphate dehydrogenase and phosphogluconate dehydrogenase and measuring the NADPH formed fluorometrically. Under the conditions of this assay 2 mol of NADPH are formed per mol of galactose-1-phosphate. The assay is linear from 0 to 1160 micrograms of galactose-1-phosphate per gram of hemoglobin. Recovery of galactose-1-phosphate added to four hemolysates averaged 99%. Galactose-1-phosphate concentrations were measured in erythrocytes from five heterozygous subjects not under dietary control and seven transferase-deficient galactosemic individuals who were receiving galactose restricted diets. In all samples from the heterozygous individuals, the galactose-1-phosphate concentrations were normal. Of the samples from galactosemic subjects, two showed extreme elevations of galactose-1-phosphate, four showed moderate elevations, and one was normal. Galactose-1-phosphate levels are used to monitor the degree of dietary control in the transferase-deficient galactosemic individual.

Adolescent↗
PubMed1992

A study of galactose intolerance in human and rat liver in vivo by 31P magnetic resonance spectroscopy.

An oral load of 20 mg/kg galactose produces significant changes in the 31P magnetic resonance spectrum of the liver of a galactosemic patient. The peak at 5.2 ppm (which includes inorganic phosphate and galactose-1-phosphate) increased on two occasions to about twice its original size 60 min after galactose administration. An oral load of 10 mg/kg galactose given to a second patient produced no discernible changes at 30 min. We have also used an animal model of galactose intolerance, in which galactose metabolism in rats was blocked by the acute administration of ethanol. Studies in vivo and in vitro showed that the increase in the peak at 5.2 ppm was largely due to galactose-1-phosphate. We have shown in this preliminary study that small amounts of galactose can produce significant elevation of hepatic galactose-1-phosphate, which can be detected by 31P magnetic resonance spectroscopy.

Adenosine Triphosphate↗
PubMed1980

Conversion of 14C-galactose into amino acids in tissue culture cells and its inhibition by manganese.

The incorporation of 14C-galactose into primary AGMK-cells was studied in the presence and absence of Mn2+. The transport of galactose into the cells is not influenced by Mn2+. 1 mM MnCl2 inhibits the incorporation of galactose into acid-precipitable material up to 50% after 6 hours incubation. In the absence of Mn2+ a substantial amount of galactose is converted to glucose, which is mainly metabolized into aspartic acid and serine. The conversion of galactose into glucose is inhibited by the addition of Mn2+. However, Mn2+ does not influence the activity of the UDP-galactose-4'-epimerase in vitro. Using the SDS-polyacrylamide electrophoresis the labelling of protein bands is similar with 14C-galactose or a 14C-amino acid mixture, respectively. In the presence of Mn2+ the incorporation of both galactose or amino acids is inhibited: With amino acids the inhibition is observed in all protein bands, whereas with galactose some bands remain unaffected. It is concluded that these are galactoproteins.

Amino Acids↗
PubMed2000

Determination of [(13)C]galactose enrichment in human plasma by gas chromatography/positive chemical ionization tandem mass spectrometry.

Galactosemia is a potentially fatal disease resulting from a deficiency of galactose-1-phosphate uridyl transferase. In order to perform mechanistic studies designed to elucidate further the etiology of the disease, we required a method to monitor (13)C enrichment in plasma galactose following a single oral dose or intravenous infusion of [1-(13)C]galactose. Determinations of plasma [(13)C]galactose enrichment requires methodology with extremely high specificity because of potential interference from other low molecular mass plasma constituents and from glucose, an isomer which is present in much higher concentrations. We have developed a method based on gas chromatography/positive chemical ionization tandem mass spectrometry (GC/PCI-MS/MS) for the precise and accurate determination of plasma [(13)C]galactose enrichment. The method employed a pentaacetylaldononitrile derivative of galactose in order to improve its GC and MS characteristics. Peak areas resulting from the transitions m/z 328 --> 106 and m/z 329 --> 107 were used to quantify the relative abundance of labeled and unlabeled galactose. Validation of the method was performed by determination of the precision and accuracy over a wide range of galactose concentrations and (13)C enrichments. The GC/PCI-MS/MS method was able to determine accurately enrichments at galactose concentrations down to 0.8 microM in the presence of 4 mM glucose, making it both highly selective and the most sensitive method currently available.

Calibration↗
PubMed2003

Stable-isotope dilution analysis of galactose metabolites in human erythrocytes.

An established gas chromatography/mass spectrometry (GC/MS) method, devised for stable-isotope dilution analysis of plasma galactose, was developed to allow determination of erythrocyte (red blood cell, RBC) concentrations of galactose-1-phosphate and other primary metabolites relevant in galactosaemia. Galactose-1-phosphate was enzymatically converted to galactose, and the aldononitrile pentaacetate derivative was separated by gas chromatography and determined by mass spectrometry using chemical ionisation and selected ion monitoring of the [MH-60](+) ion. U-(13)C-Labelled standard was used for quantification. Comparative measurements were conducted using established fluorimetric and radiometric enzymatic methods. The GC/MS analysis for galactose-1-phosphate was linear (range examined 0-600 micromol/L(RBC), packed cells), of acceptable repeatability at low and high concentrations (within and between run CVs <15%), with a limit of quantification of 0.01 micromol/L(RBC). With samples from patients with classical galactosaemia there was a linear correlation with conventional enzymatic assays (r(2) > 0.927). In erythrocytes from post-absorptive patients under treatment, Q188R-heterozygous parents, and healthy subjects, galactose-1-phosphate concentrations (mean +/- SD) were found to be 142 +/- 38 (n = 41), 1.4 +/- 0.2 (n = 8), and 1.9 +/- 0.5 (n = 33) micromol/L(RBC), respectively. In comparison, free galactose concentrations were 3.8 +/- 1.7, 0.49 +/- 0.19, and 0.43 +/- 0.20 mol/L(RBC), respectively. The procedure allowed simultaneous galactitol analysis and proved to be useful to trace incorporation of (13)C-label into erythrocyte galactose metabolites in a D-[1-(13)C]galactose in vivo turnover study.

Blood Chemical Analysis↗
PubMed1993

Galactose inhibition of the constitutive transport of hexoses in Saccharomyces cerevisiae.

The relationship between the pathways of glucose and galactose utilization in Saccharomyces cerevisiae has been studied. Galactose (which is transported and phosphorylated by inducible systems) is a strong inhibitor of the utilization of glucose, fructose and mannose (which have the same constitutive transport and phosphorylation systems). Conversely, all these three hexoses inhibit the utilization of galactose, though with poor efficiency. These cross-inhibitions only occur in yeast adapted to galactose or in galactose-constitutive mutants. The efficiency of galactose as inhibitor is even greater than the efficiencies of the other three hexoses to inhibit the utilization of each other. Phosphorylation is not involved in the inhibition and the transport of sugars is the affected step. The cross-inhibitions between galactose and either glucose, fructose or mannose do not implicate utilization of one hexose at the expense of the other, as it occurs in the mutual interactions between the latter three sugars. It seems that, by growing the yeast in galactose, a protein component is synthesized, or alternatively modified, that once bound to either galactose or any one of the other three hexoses (glucose, fructose or mannose), cross-interacts respectively with the constitutive or the inducible transport systems, impairing their function.

Adaptation, Biological↗
PubMed1981

Modulation of 75S RNA synthesis in the Balbiani rings of Chironomus tentans with galactose treatment.

Galactose has been used as a tool to modify gene activity in the giant puffs Balbiani ring 2 (BR2) and Balbiani ring 1 (BR1) on chromosome IV in the salivary glands of Chironomus tentans. BR2 decreased gradually and was absent or almost absent after a four day galactose treatment. Concomitant with this morphological change, the labelling of the population of growing 75S RNA molecules in BR2 decreased, and was essentially abolished after four days in galactose. Since the elongation rate at the 75S RNA genes proved to be the same in the galactose treated glands as in the control glands, the decreased labelling in BR2 was likely to correspond to a decreased production of 75S RNA. No changes in the size distribution of the growing 75S RNA molecules were noted during the galactose treatment, suggesting that the modulation of the activity was most likely accomplished at the initiation level, but regulation of a very early premature termination could not be excluded. When galactose was removed from the medium, BR2 attained its normal size and its ordinary RNA labelling. BR1 was studied in parallel with BR2 and it behaved strikingly different: BR1 expanded during the galactose treatment and the amount of growing 75S RNA increased, indicating an enhanced production of this 75S RNA species. Also the modulation of BR1 RNA synthesis was reversible. During the galactose treatment no changes in the labelling of chromosome I-III and of nucleolar RNA were observed suggesting that during the four day treatment, galactose exerted its effect mainly on the synthesis of BR2 and BR1 transcription products. The significance of these observations are considered in relation to the information available on the synthesis of the corresponding secretory polypeptides and the formation of the tube-like burrows. We also discuss the implications of the results for models of the regulation of gene activity and of the puffing process.

Animals↗
PubMed1993

The effect of dietary fruits and vegetables on urinary galactitol excretion in galactose-1-phosphate uridyltransferase deficiency.

Even on a lactose-restricted diet, urinary galactitol excretion and erythrocyte galactose-1-phosphate levels are persistently elevated in patients with galactose-1-phosphate uridyltransferase deficiency. In order to determine the contribution of galactose in dietary fruits and vegetables to this phenomenon, (1) the content of galactose in a lactose-free diet was directly measured when a galactosaemic patient's diet was specifically enriched in those fruits and vegetables which contain relatively large amounts of free galactose and (2) galactitol excretion was determined during ingestion of this diet for 3 weeks and while on a synthetic diet for 1 week that provided < 8 mg galactose/day. For comparison the effect of a 3-week supplementation of 200 mg galactose/day was determined. The measured intake in total foodstuffs matched the theoretical content of galactose in the patient's diet based on amounts in fruits and vegetables alone, thus supporting the concept that fruits and vegetables are primarily responsible for galactose intake in a lactose-free diet. All of the dietary manipulations, however, had relatively little effect on metabolite levels, suggesting that endogenous galactose production is primarily responsible for the elevated levels of galactose metabolites routinely detected in patients on lactose-restricted diets.

Adolescent↗
PubMed1992

Incorporation of the hexose analogue 2-deoxy-D-galactose into membrane glycoproteins in HepG2 cells.

The incorporation of 2-deoxy-D-galactose into the oligosaccharide moieties of glycoproteins and the consequences of 2-deoxy-D-galactose treatment on the fucosylation of glycoproteins were investigated in the human hepatoma cell line HepG2. Using different methods, it was shown that treatment of HepG2 cells with 2-deoxy-D-galactose leads to an incorporation of 2-deoxy-D-galactose and a decrease of L-fucose incorporation into the oligosaccharides of glycoproteins. The extent of labeling by L-[3H]fucose was determined by removing L-[3H]fucose from labeled cells with the aid of a purified alpha 1,2-fucosidase from Aspergillus niger. Using this method, it was shown that 2-deoxy-D-galactose markedly inhibits alpha 1,2-fucosylation. Measurement of the amount of 2-deoxy-D-galactose incorporated, however, showed that replacement of D-galactose by 2-deoxy-D-galactose does not entirely account for the decrease in alpha 1,2-fucosylation. In addition, a hitherto unreported compensatory increase of alpha 1,3/alpha 1,4-fucosylation was found to occur when alpha-1,2-fucosylation was inhibited by treatment with 2-deoxy-D-galactose.

Adenosine Triphosphate↗
PubMed1976

Metabolism and transport of galactose by rat intestine.

Intestinal uptake and metabolism of galactose were examined in everted jejunal rings from fasted adult rats using 0.2-28 mM sugar. After 60-min incubations, the total uptake (free tissue plus amount metabolized) of galactose ranged from 1.75 mumol/g at 0.2 mM to 21 mumol/g at 28 mM. Free tissue galactose was 17% of the former and 73% of the latter amount while that oxidized to 14CO2 represented only 6-16% of amount taken up. Compared to glucose, similar amounts of galactose are taken up at 0.2-2.0 mM, however, gllcose rtween 0.2 and 2 mM similar amounts of both sugars are metabolized, although a greater portion of the glucose is oxidized to 14CO2. Above 2.0 mM, 2-3 times more glucose is metabolized than galactose. Both uptake and metabolism showed saturability and kinetic analysis revealed two limbed Linweaver-Burk plots, suggesting operation of a high affinity low Km and a low affinity high Km system for sugar transport. In a series of in vivo studies, to assess the role of the intestine in the total body metabolism of galactose, 14C-labeled galactose injected intraperitoneally at a dose of either 50 or 300 mg into fasted normal, sham operated and enterectomized rats, no observable difference in 14CO2 production resulted in between the groups. It would thus appear that although extensive metabolism of galactose may take place in intestinal tissue in vitro, the intestine does not play a significant role in galactose disposition in vivo.

Animals↗