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Accumulation of galactonate in liver of suckling rats perfused with galactose.

Livers of 14-day-old suckling rats were perfused for 30 min in the nonrecirculating (once-through) mode with media containing 0-60 mM galactose. Galactonate was detected in livers perfused with as little as 1 mM galactose and increased with higher perfusate galactose to 178 nmoles per gram of liver at 60 mM hexose. Tissue galactonate levels were as high as 60% of galactose-1-phosphate which also accumulated under the same conditions. Galactonate was also found to be present in the effluent perfusate. The perfused suckling rat liver appears to be a physiological model for assessing the role of galactose oxidation to galactonate as an alternate metabolic pathway of galactose metabolism.

Animals↗

Structure of the extracellular polysaccharide from slime-forming Lactococcus lactis subsp. cremoris SBT 0495.

The extracellular polysaccharide obtained from slime-forming Lactococcus lactis subsp. cremoris SBT 0495 is composed of D-glucose, D-galactose, L-rhamnose, and phosphate. Methylation analysis of the native and dephosphorylated polysaccharides provided information on the linkage of the sugar residues and the location of the phosphate group. N.m.r. spectroscopy confirmed the structure of the polysaccharide, which is assigned the following repeating-unit: [formula: see text]

Carbohydrate Sequence↗

Syntheses and insulin-like activity of phosphorylated galactose derivatives.

The syntheses of the poly-phosphorylated galactosides 6, 8, 10, 13, 16, and 20, isolated as sodium salts, have been performed. The non-phosphorylated disaccharide 17 and trisaccharide 21 have been prepared via glycosylation of the 2-(trimethylsilyl)ethyl galactosides 3 and 2, respectively, and subsequent complete deprotection. Preliminary insulin-like activity of the phosphorylated derivatives is reported.

Cells, Cultured↗

Galactose and galactose-1-phosphate spot test for galactosemia screening.

A simple spot test to measure galactose and galactose-1-phosphate in blood-impregnated filter paper was studied as a screening test for galactosemia in the newborn. A 3-mm disc punched from blood-impregnated filter paper card was fixed with acetone-methanol and incubated in a reaction mixture containing galactose dehydrogenase and alkaline phosphatase. This reaction mixture was then spotted on DEAE-cellulose paper, dried, and observed under a UV-lamp. The minimum amount of galactose detected by this procedure was 2 mg/dl. Estimation of galactose and galactose-1-phosphate with this procedure correlated well with estimation by bacterial assay.

Escherichia coli↗

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↗

Erythrocyte galactokinase assay with high performance liquid chromatography.

An assay for erythtocyte galactokinase based on high performance liquid chromatographic determination of galactose 1-phosphate (Gal-1-P) is described. The determination of Gal-1-P was applied to a post-column fluorometric detection of reducing sugars using arginine. This method is as sensitive and accurate as conventional radioisotopic methods, but needs no radioisotopic facilities. It requires only a small blood sample and is suitable as a follow-up test in neonatal screening.

Adult↗

Colorimetric determination of galactose and galactose-1-phosphate from dried blood.

A colorimetric microassay for the simultaneous quantitative determination of galactose (Gal) and galactose-1-phosphate (Gal-1-P) in dried blood spots is described. An enzymatic reaction involving alkaline phosphatase (EC 3.1.3.1) and galactose dehydrogenase (EC 1.1.1.48) produces NADH, which is coupled with diaphorase (EC 1.8.1.4) and iodonitrotetrazolium violet (INT). The colourless INT is converted to a formazan of red colour the intensity of which is quantitated either photometrically by a microplate reader or determined visually with sufficient sensitivity for screening purposes. We evaluated the assay on 200,000 blood samples in a newborn screening program, and were able to distinguish between classical and milder forms of galactosemia with ease.

Alkaline Phosphatase↗

Enzymatic transfer of galactosyl phosphate from UDP-galactose to UDP-N-acetylglucosamine.

The microsomal fraction of hen oviduct homogenate has been shown to contain an enzyme capable of catalyzing a transfer of galactosyl phosphate from UDP-galactose to UDP-N-acetylglucosamine. The product was isolated and identified as UDP-N-acetylglucosamine-6-phosphogalactose, the same compound as that found as a normal constituent in hen oviduct. The enzyme is analogous in reaction type to UDP-N-acetylglucosamine: glycoprotein N-acetylglucosamine-1-phosphotransferase (the enzyme responsible for introducing the recognition marker of newly synthesized lysosomal enzymes), which suggests that the galactosyl phosphotransferase is involved in galactose 1-phosphate transfer to N-acetylglucosamine residues of newly synthesized glycoproteins.

Alkaline Phosphatase↗

Identification of galactitol 2-phosphate and galactitol 3-phosphate in the lens of galactose-fed rats.

Production of unusual phosphorylated metabolites in the lens is one of several changes caused by hyperglycemia. Sorbitol 3-phosphate (Sor-3P) and fructose 3-phosphate (Fru-3P) are two such compounds identified in the diabetic lens, and galactitol 2-phosphate (Gal-2P) and galactitol 3-phosphate (Gal-3P) are identified here in the galactosemic lens. These new compounds are the first example of galactitol metabolism in mammalian tissue other than liver. Sor-3P and Fru-3P are also present in the galactosemic lens, apparently synthesized directly from their precursors, sorbitol and fructose, which are elevated in the lens due to increased flux of glucose through the aldose reductase (AR) pathway. The NADPH necessary to support this increased flux is derived from activation of the hexose monophosphate shunt (HMPS), which is clearly demonstrated by a large increase in the concentration of sedoheptulose 7-phosphate (Sed-7P), a HMPS-specific metabolite. Additionally, during 3 weeks of galactose feeding, there is a dramatic increase in lenticular concentrations of galactitol, sorbitol, galactose, and fructose and a sharp decrease in inositol. Glucose remains unchanged. A precipitous loss of both phosphorylated and nonphosphorylated metabolites occurs after 3 weeks, possibly due to lens rupture.

Animals↗

HPLC analysis of hexosamine phosphates in biological samples.

Galactosamine is quickly metabolized to galactosamine 1-phosphate in rats treated with this compound. An HPLC method to quantify hexosamine phosphates in biological samples is described, modified from the o-phthaldialdehyde amino acid analysis procedure. o-Phthaldialdehyde derivatives of hexosamines and hexosamine-phosphates can be eluted from a reverse-phase column at different retention times, with a total analysis time of 30 min and without overlapping with free amino acids at physiological concentrations. The standard curves are linear between 1 and 40 nmol. This simple method is more selective and sensitive than previous enzymatic analyses of hexosamine phosphorylation.

Animals↗

Partial purification and characterization of an aldohexose 1-P phosphatase from pig skeletal muscle.

An enzyme with a molecular weight of 54,000 which possesses phosphatase activity acting on glucose 1-P, galactose 1-P and mannose 1-P has been partially purified and characterized from pig skeletal muscle. The enzyme is free of phosphoglucomutase and galactokinase activities, and it possesses a neutral optimum pH. Pi acts as an inhibitor; glucose, galactose and mannose do not produce any effect. Divalent cations are required for activity, Mg2+ being the most effective activator. Micromolar levels of fluoride and millimolar levels of chloride act as inhibitors; however, vanadate does not produce any effect. The enzyme may have an important role when galactose accumulates in tissues; for example, in galactosemic patients and in young animals ingesting high-galactose diets.

Animals↗