Glycerol biosynthetic pathway plays an essential role in proliferation and antioxidative defense in the human enteric protozoan parasite Entamoeba histolytica

Amebiasis is caused by the protozoan parasite Entamoeba histolytica. Treatment options other than metronidazole and its derivatives are few, and their low efficacy against asymptomatic cyst carriers, and experimental evidence of resistance in vitro justify the discovery/repurposing campaign for new drugs against amebiasis. Global metabolic responses to oxidative stress and cysteine deprivation by E. histolytica revealed glycerol metabolism may represent a rational target for drug development. In this study using 14C-labelled glucose, only 11% of the total glucose taken up by E. histolytica trophozoites is incorporated to lipids. To better understand the role of glycerol metabolism in this parasite, we focused on characterizing two important enzymes, glycerol kinase (GK) and glycerol 3-phosphate dehydrogenase (G3PDH). Recombinant GK was biochemically characterized in detail, while G3PDH was not due to failure of protein expression and purification. GK revealed novel characteristics and unprecedented kinetic properties in reverse reaction. Gene silencing revealed that GK is essential for optimum growth, whereas G3PDH is not. Gene silencing of G3PDH caused upregulated GK expression, while that of GK resulted in upregulation of antioxidant enzymes as shown by RNA-seq analysis. Although the precise molecular link between GK and the upregulation of antioxidant enzymes was not demonstrated, the observed increase in antioxidant enzyme expression upon GK gene silencing suggests a potential connection between GK and the cellular response to oxidative stress. Together, these results provide the first direct evidence of the biological importance and coordinated regulation of the glycerol metabolic pathways for proliferation and antioxidative defense in E. histolytica, justifying the exploitation of these enzymes as future drug targets.

Investigation of osmotic shock effect on pulsed electric field treated S. cerevisiae yeast cells

Pulsed electric field (PEF) treatment is known to cause plasma membrane permeabilization of microorganisms, an effect known as electroporation. PEF treatment is very attractive since it can achieve permeabilization with or without lethal damage in accordance with desired results. This study aimed to expand the accomplishment of electroporation outcomes by applying sudden post-PEF osmotic composition change of the media. Changes in yeast cells' viability, size and plasma membrane regeneration rate were evaluated. However, we still have questions about the intracellular biochemical processes responsible for plasma membrane recovery after electroporation. Our suggested candidate is the high osmolarity glycerol (HOG) kinase pathway. The HOG pathway in Saccharomyces cerevisiae yeasts is responsible for volume recovery after dangerous shape modifications and intracellular water disbalance caused by environmental osmotic pressure changes. Thus, we evaluated the HOG pathway inactivation effect on S. cerevisiae's reaction to PEF treatment. Results showed that Hog1 deficient S. cerevisiae cells were considerably more sensitive to electric field treatment, confirming a link between the HOG pathway and S. cerevisiae recovery process after electroporation. By suddenly changing the osmolarity of the media after PEF we influenced the cells' plasma membrane recovery rate, severity of permeabilization and survivability of yeast cells. Studies of electroporation in combination with various treatments might improve electric field application range, efficiency, and optimization of the process.

Pseudo-hypertriglyceridaemia in glycerol kinase deficiency misdiagnosed and treated as true hypertriglyceridaemia

High triglyceride in a serum sample with no apparent visible lipaemia is a confusing laboratory condition. This condition of apparent hypertriglyceridaemia might be an asymptomatic condition of pseudo-hypertriglyceridaemia which is seen in individuals with glycerol kinase deficiency. Glycerol is increased in glycerol kinase deficiency, therefore biochemical analysers that measure glycerol to estimate triglyceride report high triglyceride values. Clinicians are often unaware of this laboratory condition; as a result, patients are subjected to aggressive hypolipidaemic drugs and lifestyle changes, and these measures turn ineffective to lower triglyceride levels. In this report, a case of a 50-year-old Nepalese male is presented with an apparent hypertriglyceridaemia refractory to various hypolipidaemic drugs for the last 13 years until a correct diagnosis of his condition was made.

Activation of adipose tissue glycerokinase contributes to increased white adipose tissue mass in mice fed a high-fat diet

PURPOSE

Investigate the pathways of glycerol-3-P (G3P) generation for triacylglycerol (TAG) synthesis in retroperitoneal (RWAT) and epididymal (EWAT) white adipose tissues from high-fat diet (HFD)-fed mice.

METHODS

Mice were fed for 8 weeks a HFD and glycolysis, glyceroneogenesis and direct phosphorylation of glycerol were evaluated, respectively, by 2-deoxyglucose uptake, phosphoenolpyruvate carboxykinase (PEPCK-C) activity and pyruvate incorporation into TAG-glycerol, and glycerokinase activity and glycerol incorporation into TAG-glycerol in both tissues.

RESULTS

HFD increased body and adipose tissue mass and serum levels of glucose and insulin, which were accompanied by glucose intolerance. RWAT and EWAT from HFD-fed mice had increased rates of de novo fatty acid (FA) synthesis (52% and 255%, respectively). HFD increased lipoprotein lipase (LPL) activity and content in EWAT (107%), but decreased in RWAT (79%). HFD decreased the lipolytic response to norepinephrine (57%, RWAT and 25%, EWAT), β3-adrenoceptor content (50%), which was accompanied by a decrease in phosphorylated-hormone-sensitive lipase (~80%) and phosphorylated-adipocyte triacylglycerol lipase (~60%) in both tissues. HFD decreased the in vitro rates of glucose uptake (3.5- and 6-fold), as well as in glyceride-glycerol synthesis from pyruvate (~3.5-fold) without changes in PEPCK-C activity and content in RWAT and EWAT, but increased glycerokinase activity(~3-fold) and content (90 and 40%) in both tissues.

CONCLUSION

The data suggest that direct phosphorylation of glycerol by glycerokinase may be responsible for maintaining the supply of G3P for the existing rates of FA esterification and TAG synthesis in RWAT and EWAT from HFD-fed mice, contributing, along with a lower lipolytic response to norepinephrine, to higher adiposity.

Quantitative detection method of triglycerides in serum lipoproteins and serum-free glycerol by high-performance liquid chromatography

We have developed a simple and reliable method for quantitative detection of triglycerides (TG) in serum lipoproteins and serum-free glycerol (FG) by high-performance liquid chromatography (HPLC). After separation of serum constituents using a new gel-permeation column (TSK gel Lipopropak XL, Tosoh) and a new eluent (TSK eluent LP-2, Tosoh), TG and FG were detected by on-line reaction using a modified reagent which contained glycerol kinase, glycerol-3-phosphate oxidase and lipoprotein lipase. HPLC patterns showed five peaks corresponding to chylomicrons, very-low-density, low-density, high-density lipoproteins and FG. Absolute concentrations of TG in each lipoprotein fraction and serum FG were calculated from the corresponding peak areas using standard FG as a calibrator. Due to its very high sensitivity of peak detection, this method has become desirable for the analyses of lipoproteins of very low concentrations such as in cell culture systems. This technique will contribute to a better understanding of lipoprotein TG and serum FG distribution in human and nonhuman subjects.

Immunochemical characterization of the ATP-stimulated glucocorticoid-receptor-translocation promoter from various organs of rat

We previously found a novel endogenous factor in rat liver cytosol, named ATP-stimulated glucocorticoid-receptor-translocation promoter (ASTP), that increased the binding of activated glucocorticoid-receptor to nuclei in the presence of ATP. In this work, we immunized rabbits with the purified ASTP protein and characterized the antibodies with regard to titer, cross-reactivity and specificity. An IgG fraction from sera of the immunized rabbits contained specific antibodies to ASTP. The anti-ASTP IgG could precipitate the ASTP protein without the activity. Immunoblot analysis revealed a major band of 48 kDa in rat liver cytosol that migrated to the same position as the purified ASTP protein by SDS-PAGE, and an additional minor band of about 50 kDa. Monospecific antibodies purified from the IgG fraction using the antigen (the purified 48-kDa ASTP protein) immobilized on a polyvinylidene difluoride membrane also reacted with both the 48-kDa ASTP protein and the 50-kDa protein in rat liver cytosol, suggesting that this 50-kDa protein is immunologically related to the 48-kDa ASTP protein. Densitometric quantification of immunoblots demonstrated that the rat kidney cytosol contained ASTP protein at a concentration of about 20% of that of liver cytosol. Other tissues such as brain, skeletal muscle, heart, and lung, contained neither the ASTP protein nor the activity.

Effects of specimen turbidity and glycerol concentration on nine enzymatic methods for triglyceride determination

We compared the effects of specimen turbidity and glycerol concentration on nine enzymatic methods for triglyceride measurement. We assayed 51 specimens with triglyceride concentrations of 0.85-8.21 mmol/L (75-727 mg/dL) and turbidity at 420 nm equivalent to > or = 0.1 mmol/L (8.8 mg/dL) triglyceride (measured as part of our comparison method). The data were analyzed by multiple regression, which gave coefficients for the effects of glycerol concentration and the change in turbidity during the reaction. The effects of specimen turbidity and glycerol concentration were method-dependent and ranged from 6.20% to -15.67% of the measured result. The magnitude of the turbidity effect (in assays with a significant turbidity interference) was similar to that for glycerol (in assays with a significant glycerol interference). A triglyceride assay with a bichromatic measurement was less subject to interference from turbidity.

Molecular cloning of rat liver glucocorticoid-receptor translocation promoter

We previously found a new endogenous factor in rat liver cytosol, named ATP-stimulated glucocorticoid-receptor translocation promoter (ASTP), that increased the binding of activated glucocorticoid-receptor to nuclei in the presence of ATP. We have cloned and sequenced a cDNA (2989 bp) encoding the ASTP protein. An open reading frame of 524 amino acids encodes a protein with a molecular weight of 57 kDa. Amino-acid sequences of six peptides obtained by Edman degradation of various cleavage products of the purified ASTP were identified in the cDNA-derived sequence. Northern analysis of mRNA from rat liver revealed a major band of about 3.8 kb. Database searches show no homology to other known proteins from mammalian origin, however, the amino-acid sequence in the middle portion of ASTP protein shows 48% homology to glycerol kinase from Escherichia coli. The region of homology to other species may help to define sites of protein-protein interaction, as well as sites of possible interaction of ASTP with ATP.

Clinical and analytical evaluation of a continuous enzymatic method for measuring pancreatic lipase activity

We report the evaluation of a new commercial kit for the determination of pancreatic lipase activity. The kit is based on the use of a 1,2-diglyceride as substrate and a specific monoglyceride lipase. The detection step is the continuous colorimetric measurement of hydrogen peroxide produced from glycerol by glycerol kinase, glycerol-3-phosphate oxidase, and peroxidase reactions. The procedure appears to be precise (between-day CV < 9%) and the results show good correlation with those obtained by alternative procedures (vs turbidimetry, r = 0.965; vs ultraviolet absorbance-enzymatic method, r = 0.995; vs Ektachem, r = 0.976; vs immunometry, r = 0.970). However, the method is susceptible to interference by increased concentrations (> 4.5 mmol/L) of serum triglycerides. We estimated the reference interval for healthy adults to be 8-44 U/L. When we evaluated clinical efficacy by using receiver-operating characteristic curves and the overlap index, no significant differences were found between the commercial kit and a common turbidimetric assay for diagnosing patients with acute pancreatitis; both methods performed satisfactorily.

Crystallization and preliminary X-ray studies of Escherichia coli glycerol kinase

Escherichia coli glycerol kinase, a major regulatory enzyme which catalyzes the reversible MgATP-dependent phosphorylation of glycerol has been crystallized by the hanging drop vapor diffusion method at room temperature. Three different crystal forms have been obtained in the presence of glycerol and appear to be suitable for X-ray crystallographic studies. Vapor diffusion against 55% ammonium sulfate and 1% beta-octyl glucoside (pH 7.0) yields rhombohedral crystals with space group R32, a = b = 277.1 A, c = 78.7 A (hexagonal indexing) containing a dimer of Mr 112,000 in the asymmetric unit (Vm = 2.64 A3/dalton). Vapor diffusion against sodium chloride in the presence of 10% (w/v) polyethylene glycol (pH 6.5 to 7.0) yields two different crystal forms, both with space group P2(1). The first form has a = 88.1 A, b = 99.3 A, c = 114.6 A, beta = 119 degrees, the second form has a = 92.5 A, b = 117.6 A, c = 108.3 A, beta = 93.64 degrees. Addition of ADP enhances growth of the monoclinic forms. These forms appear to contain an entire tetramer of Mr 224,000 in the asymmetric unit and have Vm values of 2.28 and 2.65 A3/dalton, respectively. All forms diffract to better than 3.0 A resolution while the second monoclinic form diffracts to approximately 1.8 A.

Enzyme product blot for nondestructive assay of protein catalytic function in polyacrylamide gels

A new method that permits rapid, sensitive, and specific enzymatic assay of proteins in polyacrylamide gels is described. The enzyme product blot described in this report involves percolation of the reaction mixture through a gel containing native enzyme which converts the labeled substrate to a labeled product with differing chemical properties. A permeable membrane with specific ligand-binding properties overlies the gel and binds the enzyme product, but not the substrate, as reaction mixture is blotted vertically. This membrane is washed free of substrate and the location of the product is identified by autoradiography. The autoradiogram is compared with the stained gel in order to recover the enzyme for amino acid sequence analysis. The enzyme product blot is demonstrated using glycerol kinase and hexokinase.

Automatic luminometric kinetic assay of glycerol for lipolysis studies

A kinetic assay for glycerol based on the glycerokinase and firefly luciferin-luciferase reactions was developed for the purpose of allowing automatic analysis of large series of incubates from human fat cells. The method includes simplified sampled pretreatment and fully automated analysis, recording, and calculation of data. The upper limit of the dynamic range of the assay was extended from a glycerol concentration in cuvette of 2 up to 100 microM. This is due to a principally new method to linearize the nonlinear part of the standard curve. Recovery experiments reveal 100% glycerol recovery. Within-run and between-run precisions are high with coefficients of variation of between 1.2 and 3.7%. Samples are stable for up to 6 months in an ordinary freezer. The detection limit expressed as 2 SD of the blank result is 0.07 microM glycerol in cuvette, which is slightly lower when compared to the previous luminometric methods. The apparent blank, which is typically 0.4-1.0 microM glycerol in cuvette, has shown significant contributions only from bovine serum albumin, 0.03 microM, and glycerokinase, 0.01 microM. The analytical performance and degree of automation of the glycerol method described in this paper makes it well suited for serial studies of lipolysis in human fat cells in the presence of lipolytic or antilipolytic agents.

A kinetic colorimetric procedure for quantifying magnesium in serum

We have developed a kinetic colorimetric procedure for determination of magnesium in serum. The magnesium-dependent enzyme glycerol kinase is used to phosphorylate glycerol to glycerol 3-phosphate, the latter being oxidized to dihydroxyacetone phosphate and hydrogen peroxide by glycerophosphate oxidase. The generated hydrogen peroxide is then reduced by peroxidase with the simultaneous oxidative coupling of 4-aminoantipyrine and 2-hydroxy-3,5-dichlorobenzenesulfonate, producing a red reaction product with an absorption maximum at 510 nm. The rate of color production is proportional to the concentration of the Mg X ATP complex, which is, in turn, proportional to the magnesium concentration in serum. This method is rapid and precise, avoids the use of expensive instrumentation, is easily automated, and results compare well with those by the Du Pont aca and manual Magon sulfonate methods.

A kinetic isotope dilution assay for glycerol

Using glycerol kinase and [3H]glycerol, a kinetic isotope dilution assay for glycerol has been developed. Reactant and product are separated by stepwise elution from QAE-Sephadex. This assay is sensitive to as little as 100 pmol of glycerol, avoids numerous drawbacks of the traditional fluorescent assay, and readily detects glycerol production by fewer than 10(5) cardiomyocytes.

The potential of microbial enzymes as diagnostic reagents

There has been a rapid growth in the application of microbial enzymes for diagnosis in the area of clinical chemistry. The reasons behind this trend are discussed. Descriptions and illustrations are given of the use of microbial enzymes in the determination of metabolic marker analytes; in the assay of antibiotics, analgesic and chemotherapeutic drugs, and in the quantitation of antibody-antigen interactions.

Serum triglycerides determined colorimetrically with an enzyme that produces hydrogen peroxide

In this direct colorimetric procedure, serum triglycerides are hydrolyzed by lipase, and the released glycerol is assayed in a reaction catalyzed by glycerol kinase and L-alpha-glycerol-phosphate oxidase in a system that generates hydrogen peroxide. The hydrogen peroxide is monitored in the presence of horseradish peroxidase with 3,5-dichloro-2-hydroxybenzenesulfonic acid/4-aminophenazone as the chromogenic system. The high absorbance of this chromogen system at 510 nm affords useful results with a sample/reagent volume ratio as low as 1:150, and a blank sample measurement is not needed. A single, stable working reagent is used; the reaction is complete in 15 min at room temperature. The standard curve is linear for triglyceride concentrations as great as 13.6 mmol/L. Average analytical recovery of triglycerides in human sera is 100.1%, and within-run and between-run precision studies showed CVs of less than or equal to 1.6 and less than or equal to 3.0%, respectively. The method is suitable for automation.

Enzymatic determination of triglycerides with a system Olli 3000 analyser

We describe a totally enzymatic method for determining serum triglycerides adapted for a System Olli 3000 analyser. In this procedure triglycerides are determined by measuring free glycerol enzymatically after hydrolysis of a sample with lipase and esterase. The method utilizes two standards for calibration, includes a blank correction and requires 20 microliter of serum. Forty serum samples can be analysed in about 30 min. The procedure is linear up to a concentration of 8 mmol/l of triglycerides. The precision and sensitivity of the method are good. A comparison of this method with another enzymatic method gave the correlation coefficient 0.988 and the regression line y = 1.02x + 0.02 (n = 95).

Continuous-flow analysis for glucose, triglycerides, and ATP with immobilized enzymes in tubular form

Small-bore ("Autozyme") tubes with immobilized enzymes at the inner wall have been developed and studied for application in the Technicon "SMAC" high-speed continuous-flow biochemical analyzer. Tubes coated with glucose oxidase (D-glucose:oxygen oxidoreductase, EC 1.1.3.4) have been prepared for the assay of glucose, with colorimetric assay of the hydrogen peroxide produced; tubes coated with glycerol kinase (ATP:glycerol phosphotransferase, EC 2.7.1.30) for the enzymatic assay of triglycerides; tubes coated with hexokinase (ATP:D-hexose-6-phosphotransferase, EC 2.7.1.1) and glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate:NAD+ oxidoreductase EC 1.1.1.49) for the measurement of ATP, an intermediate product in assays for creatine kinase. With use of 10-15 cm lengths of Autozyme tube and SMAC hydraulics (150 samples per hour), assay sensitivity and carryover were similar to values for the corresponding free-enzyme methods. These immobilized enzymes were sufficiently stable for one to eight weeks of continuous use before replacemnt. We conclude that suitable bound-enzyme tubes can replace either single or multiple free-enzyme reagents in many continuous-flow assays at high sampling rates.

A sensitive radioenzymatic assay for glycerol and acylglycerols

A sensitive radioenzymatic assay for glycerol and acylglycerols is described. The assay depends on the quantitative phosphorylation of glycerol to glycerophosphate by glycerol kinase using [gamma-32P]ATP as a substrate. The 32P content of the formed glycerophosphate is determined and gives a measure of the original glycerol content. Acylglycerols can be determined by prior hydrolysis to glycerol. The assay is sensitive to about 0.1 nmol of glycerol and can be extended to 100 nmol. The assay can be applied to the determination of acylglycerols separated by thin-layer chromatography in amounts as low as 0.5 nmol. The assay is particularly useful in the determination of the specific activity of 14C- or 3H-labeled glycerol moeities.

[Biokinetic characterization of human glycerin utilization]

23 patients received controlled infusions of 10% glycerol solution using an "Infusomat". During various rates of infusion biokinetic parameters and renal excretion were measured. The concentration of glycerol in the serum rises over-proportional with increasing rates of infusion. The extrapolated maximal metabolic turnover capacity is 54 micronmol.kg-1.min-1. Halb-maximal turnover rate is reached at a serum level of 0,56 micronmol.ml-1. After an infusion of 0,3 g.kg-1.min-1 glycerol disappears from the blood with an elimination constant of 0,024 min-1 and a half life of 28,9 minutes. Renal excretion increases with the dose but remains below 10% of the dose in the investigated range. From the data it can be concluded that glycerol cannot be applicated in higher doses than other polyols. No adverse reactions have been observed in the range up to 0,3 g.kg-1.min-1.

A semi-automated enzymatic assay for free glycerol and triglycerides in serum or plasma

1. A relatively inexpensive semi-automated enzymatic procedure is described for the determination of total glycerol with an Auto Analyzer. Free glycerol is determined without saponification in a deproteinized supernatant. 2. The dilution of triglyceride samples during preparation is such that the samples during preparation is such that the samples can be quantified directly from the free glycerol standards by multiplying by 100. 3. A pyruvate kiluent solution is used in the triglyceride sample preparation to increase the precision by improving the accuracy in determining blank optical densities. 4. The end-point reaction is complete in eight minutes, and the assay is linear up to 6 mg% free glycerol or 600 mg% triglycerides. The within-run and between-run coefficients of variation were both 1.5% for the glycerol assay, and 1.0% and 4.3% for the triglyceride assay. The mean recovery of added glycerol was 100.7% and 102.3% for the glycerol and triglyceride assays respectively.

Evaluation of a new enzymatic kit for serum triglycerides

We evaluated a new enzymatic kit for serum triglycerides (triacylglycerols) in two laboratories. The procedure involved both enzymatic hydrolysis of the triglycerides and conversion of the glycerol, which was linked to an indicator reaction. There was excellent agreement with the mechanized procedure of Kessler and Lederer and with a manual method. The test requires 50 mul of serum and can be completed in about 50 min. Inter- and intra-laboratory variation, linearity, accuracy, and specimen storage were studied.

Fluorine as a hydroxy analogue. Stereospecific phosphorylation of 2-deosy-2-fluoroglycerol by glucerol kinase

Glycerol kinase catalyses the phosphorylation of the symmetrical substrate, 2-dexoy-2-flurooglycerol, by ATP to an asymmetric product, 2-deoxy-2-fluoro-sn-glycerol 3-phosphate. The stereospecificity of the enzymic reaction was extablished by unambiguous chemical synthesis of 2-deoxy-2-fluoro-sn-glycerol labelled with 2H at C-1, followed by glycerol kinase-catalysed phosphorylation and isolation of the labelled phosphate. The configuration of the 2H-labelled phosphate was determined by n.m.r. spectroscopy. This enzymic phosphorylation of 2-dexoy-2-fluoroglycerol is absolutely stereospecific in the same sence as that of glycerol, with fluorine replacing the C-2 hydroxy group. The behaviour of fluorine as a hydroxy analogue in directing the stereospecific course of the enzyme reaction is relevant to the use of the fluorine atom of fluoro analogues of substrate as a reporter group for hydroxy-binding sites of enzymes.

Glyceraldehyde phosphate at the reducing terminus of Salmonella Q haptens. Salmonella montevideo

The O antigen polysaccharide of Salmonella montevideo was isolated from a core-defective mutant by the phenol/water procedure, and was suspected to contain phosphomonester and cyclic phosphodiester at its reducing end in anology to the O hapten from Salmonella typhimurium (Kent and Obsborn, 1968. Therefore, it was chromatographed on a DEAE-cellulose column. Whereas one part eluted with water the other part of the polysaccharide could only be eluted with buffer. Both fractions were further purified on Sephadex G100 and contained mannose, glucose, N-acetylglucosamine and phosphate in a molar ratio of 4:1:1: less than 0.1. In order to specifically label the reducing end phosphate was removed enzymatically, or the presumed cyclic diester was cleaved by mild hydrolysis, and the fractions were reduced with sodium horo[3H]hydride. Both fractions yield mainly [3H]glycerol after hydrolysis and paper chromatogaphy. In addition, [3H]mannitol and [H]monohydroxyacetone could be identified by paper chromatography and were concluded to be the result of phosphate migration and beta-elimination reactions taking place during the isolation procedure and the various treatments prior to sodium boro[3H]hydride reduction. These findings in addition to periodate oxidation studies indicated that the O antigen polysaccharide of Salmonella montevideo had glyceraldehyde phosphate at its reducing end. From the incorporation of 3H into the polysaccharide the O antigen was calculated to consist of about 19 repeating units of 6 sugar residues each.