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Disorders of galactose metabolism.

Galactose metabolism occupies a central position in modern biology through its relationship to cell surface antigenicity and its metabolic function as a component of glycolipids and glycoproteins. Disturbances in three fundamental reaction sequences of this hexose have led to a delineation of pathways of the chemistry resulting in the understanding of its metabolic fate. These inherited disorders of metabolism are prototypes for the application of nutritional therapy of biochemical genetic defects.

Animals↗
PubMed1976

The effect of pH on incorporation of galactose by a normal human cell line and cell lines from patients with defective galactose metabolism.

Incorporation of radioactive galactose into TCA-insoluble material of galactosemic fibroblasts is more sensitive to low pH than is the incorporation by normal human fibroblasts. This study was undertaken to determine (1) whether there was any pH which could correct or counteract the galactosemic defect relative to galactose incorporation, and (2) whether the low pH effect was specific for galactose metabolism or whether general cellular metabolism in galactosemic cells was more sensitive to low pH than that in normal cells. The pH dependencies of incorporation of radioactive galactose and glucose into cellular macromolecules were investigated in galactosemic and normal cells. Normal cells have a biphasic curve with respect to galactose incorporation with peaks at pH 7.0 and 8.5. Galactosemic cells have only the high pH peak. The maximum incorporation by galactosemic cells was never more than about 30% that seen by normal cells under the conditions of these experiments. Thus manipulation of the pH alone cannot correct the galactosemic defect. The rate of incorporation of radioactive galactose was studied in normal, galactosemic and galactokinase deficient cells, at pH 7.2 and at pH 6.3. At pH 7.2, galactosemic cells incorporate galactose at a linear rate which is 30 to 40% that of normal cells while incorporation by kinase-deficient cells is between 5 and 10% of normal. At pH 6.3, the incorporation is also linear. However, galactosemic cells now exhibit the same rate as kinase-deficient cells in which the low level of incorporation is unaffected by pH. These results suggest that incorporation of galactose by galactosemic cells at low pH is not due to metabolic death of the cells, but may be due to the inhibition of some specific step or steps along a metabolic route of galactose metabolism other than the Leloir pathway.

Cell Line↗
PubMed1976

[Screening of newborns for inborn errors of galactose metabolism. Methods and results].

Three inborn errors of galactose metabolism as known today. Only two of them cause illness: the deficiencies of galactokinase and of galactose-l-phosphate uridyltransferase. Both can be detected through mass screening of newborns and are amenable to a simple and successful dietary treatment. Mass screening of newborns for disorders of galactose metabolism can be performed efficiently and inexpensively if it is incorporated in the general newborn screening program.

Biological Assay↗
PubMed1978

Galactose metabolism in Dictyostelium discoideum. Regulation of galactose-1-phosphate-uridyl transferase during growth and development.

Dictyostelium discoideum is able to metabolize [1-14C]galactose to 14CO2 despite the observation that galactose is inhibitory with respect to growth. Galactose-1-phosphate uridyl transferase activity is present throughout growth and development and varies in activity only slightly during the entire life cycle of D. discoideum, in contrast to the rapid increase in UDP-glucose 4-epimerase activity during development. Therefore, in D. discoideum, these two enzymes of the Leloir pathway are independently regulated, unlike E. coli where these enzymes are coordinately controlled.

Dictyostelium↗
PubMed2026

Development and internal validation of a six-gene prognostic model based on galactose metabolism for overall survival in lung adenocarcinoma.

BACKGROUND: Lung cancer remains a leading cause of cancer incidence and mortality globally. Metabolic reprogramming promotes tumor progression and shapes an immunosuppressive tumor microenvironment. Galactose metabolism is involved in multiple malignancies, but its prognostic value in lung adenocarcinoma (LUAD) remains unclear. This study aimed to develop and internally validate a galactose metabolism-related multigene prognostic model for LUAD. METHODS: A retrospective prognostic model development and internal validation study was performed using RNA sequencing (RNA-seq) and clinical data from 585 LUAD patients in The Cancer Genome Atlas (TCGA). Differential expression, functional enrichment, univariate and multivariate Cox regression were applied to construct a prognostic gene signature. Internal validation was performed using bootstrap resampling. Model performance was evaluated by time-dependent receiver operating characteristic (ROC), C-index, calibration, and Kaplan-Meier analysis. Associations between the model and immune infiltration, immunotherapy responsiveness, and tumor stemness were also analyzed. RESULTS: A six-gene prognostic model (GALT, GANC, PGM1, GALM, B4GALT1, PGM2) was developed. The model showed good discrimination with 1-, 3-, and 5-year area under the curve (AUC) values of 0.719, 0.693, and 0.684, respectively. The low-risk group exhibited significantly longer survival, increased antitumor immune infiltration (CD8+ T cells, M1 macrophages, activated CD4+ memory T cells), higher expression of T cell proliferation-related genes, lower immune checkpoint expression, better predicted immunotherapy response, and lower tumor stemness compared with the high-risk group. CONCLUSIONS: We developed and internally validated a six-gene prognostic model for LUAD based on galactose metabolism. The model shows moderate prognostic performance and is associated with antitumor immunity and tumor stemness. It may be used for prognostic risk stratification and to guide personalized immunotherapy in LUAD.

Galactose metabolism↗
PubMed1979

Galactose metabolism in isolated perfused suckling-rat liver.

The metabolic conversion of 1, 2, or 4 mM galactose to glucose was studied in isolated livers of suckling rats. Whereas galactose uptake during perfusion with 1 and 2 mM galactose was linear throughout the 90-min experiment, uptake was delayed for 35 min when 4 mM galactose was perfused. Studies with radioactive galactose revealed a parallel disappearance of galactose and the appearance of [14C]glucose; about 80% of the galactose taken up was converted to glucose. Galactose perfusion appeared to reduce the basal amount of glucose derived from substrates other than galactose. The specific activities in the galactose-perfused livers of the three major galactose metabolizing enzymes, galactokinase, galactose-1-phosphate uridylyltransferase, and uridine diphosphogalactose-4-epimerase, revealed that the transferase was significantly lower, whereas that of galactokinase and epimerase were significantly higher than in livers perfused without galactose. No meaningful changes were observed in the levels of either phosphorylated or uridylated hexoses in these studies.

Animal Population Groups↗
PubMed1977

Comparative studies of glucose-fed and glucose-starved hamster cell cultures: responses in galactose metabolism.

The metabolic flow of trace amounts of D-[14C]-galactose was followed in cultures of transformed and untransformed hamster cells over a period ranging from five minutes to two hours. The results of chromatographic and enzymatic analyses of the soluble pools are described. Non-glycolytic cells(previously deprived of sugar periods of up to 24 hours) convert D-galactose to galactose-1-phosphate and uridine diphosphoglucuronic acid in 10 to 20 minutes. In the same short assay time, glycolytic cells which have been maintained for 24 hours in media containing glucose or galactose convert D-galactose to uridine diphsphogalactose and uridine diphosphoglucose (ratio 1.4:1). Long term diprivation of sugar also results in 3- to 4-fold increases in the uptake of galactose. In addition, the incorporation of galactose label into chloroformethanol soluble material appears to be influenced by the culture conditions of the untransformed cells while incorporation in the transformed cells appears unaffected. When cycloheximide is included in the maintenance medium for extended periods, the non-glycolytic cells also show increases in galactose uptake rates but the glucose-fed, glycolytic cells llose uptake ability. UDPhexose is the main galactose metabolic peak in the soluble pools of the cycloheximide-treated, glycolytic and the cycloheximide-treated, non-glycolytic cells. The results of these experiments suggests that uptake of galactose and its subsequent metabolism are under separate control.

Animals↗
PubMed1979

[Hereditary abnormalities of galactose metabolism: diagnosis and biochemical supervision (author's transl)].

The authors define the main stages of the biochemical study of hereditary abnormalities of galactose metabolism. They review laboratory examinations for detection, enzyme examinations which provide the diagnostic proof, further examinations which permit one to follow the course and efficacy of a galactose-free diet, the demonstration of genetic variants, the technics of antenatal diagnosis and routine neonatal detection.

Biological Assay↗
PubMed1975

[Activity of enzymes of galactose metabolism in so-called congenital cataract (author's transl)].

Activity of galactokinase (69 subjects) and galactose-1-phosphate uridyl transferase (92 subjects) were measured in haemolysed blood from children (predominantly of school age) with congenital cataract. chi2 tests, gene-frequency determination and metabolic-kinetic studies indicated that the changes in the lens in congenital cataract are partly due to a manifest or latent disorder of galactose metabolism, in particular a glactose-1-phosphate uridyl transferase defect.

Austria↗
PubMed1976

The metabolism of carbohydrates by extremely halophilic bacteria: identification of galactonic acid as a product of galactose metabolism.

Cell-free extracts prepared from the extremely halophilic bacterium Halobacterium saccharovorum oxidize galactose and accumulate a product which reacts as if it were a lactone. The product does not act as a reducing sugar and contains all six of the carbon atoms initially present in galactose. The product was jugged to be galactonic acid, based on the behavior of the acetylmethyl ester derivative of the product and the pentaacetyl derivative of the galactonic methyl ester during gas chromatography.

Alcohol Oxidoreductases↗
PubMed1977

2-Deoxy-D-galactose metabolism in ascites hepatoma cells results in phosphate trapping and glycolysis inhibition.

The metabolism of 2-deoxy-D-galactose has been studied in AS-30D rat ascites hepatoma cells in suspension. Using 2-deoxy-D-(1-14C)galactose and an alkaline ethanol deproteinization procedure, the quantitatively identified metabolites included 2-deoxy-D-galactose 1-phosphate comprising 99.3%, and UDP-2-deoxy-D-galactose and UDP-2-deoxy-D-glucose, together amounting to 0.4% of the total metabolites. After incubation for 5 h in the presence of 2-deoxy-D-galactose (1 mmo1/1), the content of 2-deoxy-D-galactose 1-phosphate reached 35 mmo1x(kg cells)-1. The rate of phosphorylation of 2-deoxy-D-galactose was rapid during the first 30 min and decreased to approximately 20% of this rate during the subsequent hours. The rapid trapping of Pi in the form of 2-deoxy-D-galactose 1-phosphate resulted in a depression of free intracellular Pi in spite of a concomitant increase in net 32Pi uptake from the medium and a decrease of ATP and other 5'-nucleotides. The rates of glucose utilization and lactate production were depressed by more than 80% in the presence of 2-deoxy-D-galactose (1 mmo1/1). Interruption of Pi trapping by removal of 2-deoxy-D-galactose from the medium reversed the depressions of Pi and ATP and resulted in a rapid but incomplete relief of glycolysis inhibition. Crossover analysis of glycolytic intermediates indicated an inhibition at the 6-phosphofructokinase step. The depression of glucose utilization may be mediated by the increased level of glucose 6-phosphate, a potent inhibitor of hexokinase. An additional inhibitory effect of a metabolite of 2-deoxy-D-galactose at the 6-phosphofructokinase step was indicated by crossover analysis after reversal of Pi and ATP depressions in the presence of a high intracellular content of 2-deoxy-D-glactose 1-phosphate. The quantitative analysis of the metabolites of 2-deoxy-D-galactose demonstrated the predominance of the monophosphate and the negligible formation of UPD derivatives of this sugar analog in AS-30D hepatoma cells. This provides a system for the investigation of a galactose analog as a phosphate-trapping agent in the virtual absence of uridylate trapping.

Adenosine Triphosphate↗
PubMed1975

Galactose metabolism in relation to cataract formation in marsupials.

Erythrocytic galactokinase and/or galactose-1-phosphate uridyl transferase activity were low in many species of marsupials. However, cataract formation was observed only in pouch-young members of these species when reared on cow's milk. The galactose tolerance of young kangaroos was found to be greatly impaired, but improved rapidly and markedly at the stage of which the definitive structure of the ruminant type of stomach as in adults is formed. The combination of high absorption of galactose and low levels of galactokinase and/or transferase thus appears to determine the predisposition of pouch-young marsupials to galactose cataractogenesis.

Adult↗
PubMed1977

Enzymes of galactose metabolism in human hair roots.

Micro-methods, making use of radioactive substrates, are described for the quantitative estimation of galactokinase and galactose-1-phosphate uridyl transferase activities in lysates of hair roots obtained from the human scalp. Enzyme assays can be carried out with fractions of one hair root. Both enzymes have been investigated with regard to stability, pH optimum and Michaelis-Menten constants. Along with similarities there were also certain differences as compared to galactokinase and galactose-1-phosphate uridyl transferase activities in other human tissues. The findings were used to optimise and standardise a radiochemical micro-assay for both enzymes in human hair root lysates, applicable to carrier detection studies in galactosaemia, an inborn error of carbohydrate metabolism. Because they can easily be obtained, hair roots are a very suitable biopsy material for both fundamental and diagnostic investigations of these enzymes.

Clinical Enzyme Tests↗