Oxidation Of Fructose Research Articles

Selective inhibition by neuraminidase of insulin action on hexose metabolism of mouse adipocytes

Mouse adipocytes treated with neuraminidase showed a decreased response of glucose oxidation to insulin although insulin binding to the cells was normal. The decreased response was associated with the release of sialic acids from the cells by enzyme digestion. The hormone action on 2-deoxyglucose uptake was also decreased. However, the hormone action on glyceride-glycerol synthesis or lipogenesis from glucose was unaltered when enzyme-treated cells were incubated with higher glucose concentration (greater than or equal to 5 mM). However, at lower glucose concentrations (< 5 mM), in which glucose transport was a rate-limiting step, the hormone action was markedly decreased. When fructose was used as a substrate, the enzyme-treated cells showed an impaired response to insulin in fructose oxidation but not in glyceride-glycerol synthesis and lipogenesis from fructose. These results suggest that the postreceptor systems of insulin action on glyceride-glycerol synthesis and lipogenesis from hexose are different from those of the hormone action on hexose transport and oxidation. Furthermore, alteration in insulin-sensitive metabolic profiles may be caused, in part, by changes in glycoproteins and/or glycoplipids on the cell surface.

The comparative oxidation of glucose, fructose, sorbitol and xylitol in normal man

The comparative oxidation of glucose, fructose, sorbitol and xylitol in normal man

Mode of action of alpha-chlorohydrin as a male anti-fertility agent. Inhibition of the metabolism of ram spermatozoa by alpha-chlorohydrin and location of block in glycolysis.

1. The effect of alpha-chlorohydrin on the metabolism of glycolytic and tricarboxylate-cycle substrates by ram spermatozoa was investigated. The utilization and oxidation of fructose and triose phosphate were much more sensitive to inhibition by alpha-chlorohydrin (0.1-1.0mm) than lactate or pyruvate. Inhibition of glycolysis by alpha-chlorohydrin is concluded to be between triose phosphate and pyruvate formation. Oxidation of glycerol was not as severely inhibited as that of the triose phosphate. This unexpected finding can be explained in terms of competition between glycerol and alpha-chlorohydrin. A second, much less sensitive site, of alpha-chlorohydrin inhibition appears to be associated with production of acetyl-CoA from exogenous and endogenous fatty acids. 2. Measurement of the glycolytic intermediates after incubation of spermatozoal suspensions with 15mm-fructose in the presence of 3mm-alpha-chlorohydrin showed a ;block' in the conversion of glyceraldehyde 3-phosphate into 3-phosphoglycerate. alpha-Chlorohydrin also caused conversion of most of the ATP in spermatozoa into AMP. After incubation with 3mm-alpha-chlorohydrin, glyceraldehyde 3-phosphate dehydrogenase and triose phosphate isomerase activities were decreased by approx. 90% and 80% respectively, and in some experiments aldolase was also inhibited. Other glycolytic enzymes were not affected by a low concentration (0.3mm) of alpha-chlorohydrin. Loss of motility of spermatozoa paralleled the decrease in glyceraldehyde 3-phosphate dehydrogenase activity. alpha-Chlorohydrin, however, did not inhibit glyceraldehyde 3-phosphate dehydrogenase or triose phosphate isomerase in sonicated enzyme preparations when added to the assay cuvette. 3. Measurement of intermediates and glycolytic enzymes in ejaculated spermatozoa before, during and after injection of rams with alpha-chlorohydrin (25mg/kg body wt.) confirmed a severe block in glycolysis in vivo at the site of triose phosphate conversion into 3-phosphoglycerate within 24h of the first injection. Glyceraldehyde 3-phosphate dehydrogenase activity was no longer detectable and both aldolase and triose phosphate isomerase were severely inhibited. Spermatozoal ATP decreased by 92% at this time, being quantitatively converted into AMP. At 1 month after injection of alpha-chlorohydrin glycolytic intermediate concentrations returned to normal in the spermatozoa but ATP was still only 38% of the pre-injection concentration. Motility of spermatozoa was, however, as good as during the pre-injection period. The activity of the inhibited enzymes also returned to normal during the recovery period and 26 days after injection were close to pre-injection values. 4. An unknown metabolic product of alpha-chlorohydrin is suggested to inhibit glyceraldehyde 3-phosphate dehydrogenase and triose phosphate isomerase of spermatozoa. This results in a lower ATP content, motility and fertility of the spermatozoa. Glycidol was shown not to be an active intermediate of alpha-chlorohydrin in vitro.

Fructose, a substrate for energy-yielding metabolism in the heart?

Effects of fructose and glucose on cardiac function and 14CO2 production from radioactive hexoses were studied in isolated working guinea pig hearts perfused at constant filling pressure via the left atrium. When hearts were perfused without exogenous substrates external work declined, indicating exhaustion of endogenous energy sources. It was possible to restore left ventricular function with concentrations of glucose in the physiological range; in order to achieve a similar restoration with fructose as the only exogenous substrate concentrations higher than 40mM were necessary. 14CO2 necessary. 14CO2 production from [U-14C]glucose was half-maximal at about 2mM glucose. On the other hand, 14CO2 production from [U-14C]fructose did not show saturation kinetics and, at concentrations around 2mM, was less than 5% of the rates observed with [U-14C]glucose. Moreover, fructose oxidation was suppressed in the presence of 5mM glucose. The data suggest that fructose cannot serve as a major substrate in the heart under in vivo conditions.

LIGHT PRODUCTION IN ALKALINE MIXTURES OF REDUCING AGENTS AND DIMETHYLBIACRIDYLIUM NITRATE*

Abstract— Kinetic studies were made of light production and 02 absorption elicited by treatment of dimethylbiacridylium hydroxide [D(OH)2] with reducing agents in alkaline aqueous solutions. D(OH)2 addition stimulated O2 uptake which proceeded with zero‐order kinetics until nearly all of the O2 or of the D(OH)2 was converted to end products. At the termination of the reactions with fructose as reductant the D(OH)2 was converted to methylacridone and to dimethylbiacridene each compound accounting for approximately one‐half the D(OH)2 consumed. O2 was reduced to H2O2. With hydroxylamine as the reducing agent the emitted light intensity was related to the first power of the D(OH)2 concentration and the rate of O2 uptake to the square root of the D(OH)2. The disappearance of D(OH)2 in these circumstances was by a first order or pseudo‐first order rate. Fructose as a reducing agent by contrast resulted in an O2 uptake nearly independent of D(OH)2 concentration over a range from 1 × 10‐5M‐1 × 10‐4M, while the light intensity and disappearance of D(OH)2 followed a one‐half order rate. O2 uptake was by zero order kinetics and the oxidation of fructose proceeded at the same rate as was found with ferricyanide as oxidant. The kinetics, quantum yields and temperature dependence of the fructose reactions were compared with similar reactions employing H2O2 as the light eliciting reagent. The results are interpreted as indicating that D(OH)2 acts as a chain initiator in a manner analogous to better known, radical producing compounds found to accelerate hydrocarbon autooxidations.

Metabolic consequences of a block in the synthesis of 5-keto-D-fructose in a mutant of Gluconobacter cerinus.

A mutant of Gluconobacter cerinus var. ammoniacus, IFO 3267, has been isolated which is deficient with respect to fructose 5-dehydrogenase, the enzyme catalyzing the oxidation of d-fructose to 5-keto-d-fructose (5 KF). Growth of this mutant on fructose as the sole carbon source was impaired unless the culture medium was supplemented with 5 KF. Significant randomization of the 1 and 6 positions of fructose has been reported previously for the wild-type organism during growth on this ketohexose. The pattern of (3)H incorporation into the C5 position of ribonucleic acid-ribose when the mutant was grown on [1-(3)H]fructose and [6-(3)H]fructose in the presence of 5 KF indicated that such randomization did not occur in this variant. The randomization observed in the wild type is, therefore, a consequence of the partial oxidation of fructose to the symmetrical 5 KF intermediate prior to its conversion to pentose. When the mutant was grown on [1-(3)H]fructose in the presence of unlabeled 5 KF, [5-(3)H]fructose appeared in the culture medium. Thus, 5 KF served as the oxidant for the nicotinamide adenine dinucleotide phosphate, reduced form, generated during growth on fructose.

Oxidative and glycolytic activity of chicken and turkey spermatozoa

1. 1. The metabolism of chicken and turkey spermatozoa was compared under identical conditions. 2. 2. The endogenous respiratory rate of turkey sperm was significantly lower than chicken spermatozoa after 60 min of incubation at 41°C. 3. 3. Acetate and succinate stimulated the respiratory rate of chicken sperm, whereas myo-inositol increased the respiration of turkey spermatozoa. 4. 4. The respiration rate of both cells was stimulated by glucose and fructose 5. 5. Acetate conversion to CO 2 was highest by chicken spermatozoa while the oxidation of fructose and glucose was greatest by turkey sperm. 6. 6. Chicken sperm exhibited a higher glycolytic rate than turkey spermatozoa. 7. 7. Pentose phosphate shunt does not appear to exist in either species.

Cell-associated fatty acid levels and energy-requiring processes in mouse adipocytes.

Cell-associated fatty acid levels and energy-requiring processes in mouse adipocytes.

The utilization of 2-ketogluconate by Hydrogenomonas eutropha H 16.

During growth ofHydrogenomonas eutropha H 16 on 2-ketogluconate, 2-ketogluconate kinase and 2-keto-6-phosphogluconate reductase were formed. These enzymes were absent from cells grown on fructose, gluconate, acetate, succinate or autotrophically. There was no evidence for extracellular oxidation of glucose, fructose or gluconate with the formation of ketogluconic acids.

Oxidative metabolism of glucose, fructose and galactose by normal and glucose-6-phosphate dehydrogenase-deficient human red cell haemolysates

Production of 14CO 2 from [U- 14C]fructose and [I- 14C]galactose by normal and glucose-6-phosphate dehydrogenase (G-6-PD)-dencient human red cell haemolysates has been shown to be dependent on exogenous NADP concentration. The optimum concentration in each case was found to be 1 m M. The effects of adding unlabeled hexose phosphates on the oxidation of 14C-labeled glucose, fructose and galactose, and on the same substrates in the presence of hexokinase are reported and discussed. The results provide no evidence of an oxidative pathway other than the conventional pentose phosphate pathway.

Kinetic Studies of the Oxidation of Fructose by Ammoniacal Silver Nitrate

Kinetic Studies of the Oxidation of Fructose by Ammoniacal Silver Nitrate

Effects of deoxyfrenolicin on isolated adipose cells—I: Glucose and fructose utilization

Deoxyfrenolicin, at an optimal concentration of about 15 to 20 μg ml , stimulated to a greater extent than did insulin the oxidation of glucose and fructose, presumably via the pentose cycle, by isolated adipose cells. Stimulation of glucose uptake and lipogenesis from glucose and fructose were lower than by insulin, however. At a higher concentration (60 μg ml ) of deoxyfrenolicin, the stimulatory effects were reduced or abolished. Deoxyfrenolicin, at a suboptimal concentration (10.5 μg ml ), stimulated still further the maximally stimulated lipogenesis from glucose and fructose in response to insulin or several “insulin-like” proteases. It is suggested that deoxyfrenolicin stimulated sugar utilization in isolated adipose cells, at least in part, through a mechanism different from the actions of insulin or proteases.

Effects of Bacillus subtilis protease, type VIII (subtilopeptidase A) on isolated adipose cells Fructose utilization and its inhibition by avenaciolide, piericidin A and puromycin

1. 1. It was found that Bacillus subtilis protease, Type VIII (subtilopeptidase A, EC 3.4.4.16), like insulin, stimulated fructose utilization (oxidation and lipogenesis) by isolated adipose cells. The optimum concentration was comparable to the required for maximal stimulation of glucose utilization, about 5 μg/ml, and higher enzyme concentrations resulted in a reduced stimulation. Insulin and B. subtilis protease induced a higher υ max for the utilization of glucose and fructose. Insulin, but not B. subtilis protease, lowered the apparent K m values of either glucose or fructose utilization to about one half of the basal values. 2. 2. The basal and the elevated oxidation of fructose was not affected by palmitic acid, although its conversion to fatty acid was greatly reduced, and its conversion to glyceride-glycerol was stimulated. The protease, like insulin, reduced the oxidation of palmitic acid and enhanced its esterification in the presence of fructose. 3. 3. From the evidence obtained through the use of avenaciolide, piericidin A and puromycin, it is suggested that the basal and the insulin- or the protease-stimulated glucose and fructose uptake pathways may be different in isolated adipose cells, and that glucose and fructose uptake may again not be effected through identical mechanisms. Moreover, the kinetic data also suggested that B. subtilis protease stimulated glucose and fructose utilization by a mechanism quite distinct from that of insulin.

Removal of sugars by activated sludge

1. (1) The diurnal variation of concentration of sugars and volatile fatty acids in fresh and settled sewage at three sites was determined. Little loss of sugar occurred on settlement at two sites, where settlement was carried out aerobically. 2. (2) The sugars normally present in sewage were removed from solution by activated sludge at much the same rate as was added glucose (40–50 mg/g/hr). 3. (3) The Michaelis constants for sugars were in the region of 10 mg/l at 20°. 4. (4) No simple relation was found between BOD loading and the ability of a sludge to remove sugars, but in general the higher the “sugar loading” the greater the activity of the sludge. 5. (5) Activated sludge acquired very high, though variable, activity towards glucose on addition of this sugar to the sewage treated but, unlike pure cultures of two species of bacteria tested, the sludge lost this activity when fed with further amounts of the sugar alone in quick succession. 6. (6) Evidence of sequential oxidation of glucose and fructose was inconclusive. 7. (7) At the point of complete, or near complete, removal of sugar from solution, variable proportions of the theoretical amounts of oxygen were taken up, namely 10–30 per cent for glucose and 8–26 per cent for sucrose. 8. (8) No evidence of formation of significant amounts of poly-β-hydroxybutyric acid was found in activated sludge grown on sewage receiving normal amounts of glucose, though the presence of 0–5 per cent polymer in sludge was established. 9. (9) It is concluded that biochemical removal of soluble substrates is not a limiting factor in the activated-sludge process, so that any limitation on the load applied would appear to involve flocculation or separation of sludge particles.

Effect of 2-Deoxyglucose on Bovine Spermatozoan Metabolism and Preservation

Bovine spermatozoa were used to test the effectiveness of the glucose analog, 2-deoxyglucose (2DG), as a reversible inhibitor of spermatozoan glycolysis, with its possible use as a spermatozoan preservative under practical storage conditions. The results showed that 2DG was an effective inhibitor of spermatozoan glycolysis, with fructolysis being more sensitive to the inhibitory action of 2DG than glucolysis. This inhibition was reversed by adding glucose. The oxidative metabolism of pyruvate and lactate was not inhibited by concentrations of 2DG which completely inhibited the oxidation of fructose. The oxidation of glucose-1-, glucose-6-, and fructose-6-phosphates was inhibited by 2DG. Thus it appears that the analog inhibits at several enzyme steps in the Embden-Meyerhof pathway of glycolysis, but the primary inhibition appears to be on the hexokinase enzyme for fructose. During longer storage, when motility was inhibited and recovered by addition of glucose, recovery became more difficult with longer storage. Thus the addition of 2DG appeared detrimental to livability of the cells under the conditions employed and consequently cannot be used as a metabolic control mechanism for preserving spermatozoa.

THE AEROBIC METABOLISM OF RAM SPERMATOZOA

Summary. The relative contributions of fructose, lactate, acetate, citrate and inositol to the aerobic metabolism of ram spermatozoa have been examined in various combinations of these substrates. By using isotopically labelled compounds it was shown that fructose and lactate were important substrates oxidized by ram spermatozoa incubated in diluents containing fructose and low levels of other metabolites. Although the addition of sodium lactate to a spermatozoal suspension caused no change in the amount of fructose converted to lactate, there was a reduction in the amount of fructose oxidized to carbon dioxide. At the levels of acetate and citrate occurring in semen, their effect on the oxidation of fructose by ram spermatozoa was small. Higher concentrations of these compounds, however, caused a decrease in fructose oxidation. The addition of citrate and acetate to a fructosecontaining diluent did not affect the amount of fructose utilized by ram spermatozoa. While acetate had no effect on the accumulation of lactate from fructose, the presence of the high levels of citrate decreased the amount of lactate produced. Thus fructose and lactate are the main metabolites for unwashed ram semen incubated under aerobic conditions in a diluent containing fructose. In these circumstances, a quantitative measure of the oxidation of these substrates, coupled with an estimation of fructolysis, should give a good measure of the metabolism of the cell.

Kinetic Study of the Oxidation of Fructose by Ceric Sulphate in Aqueous Sulphuric

Kinetic Study of the Oxidation of Fructose by Ceric Sulphate in Aqueous Sulphuric

Effects of ions and of washing on the aerobic metabolism of dog spermatozoa.

Summary. The metabolism of dog spermatozoa in the presence of various ions has been studied. Of the ions tested, potassium had the greatest effect and at least doubled the respiration of washed cells. It did not, however, significantly change aerobic fructolysis. Due to interaction with other diluent components, magnesium ions had variable effects on respiration. Thus magnesium enhanced fructose oxidation in the presence of low levels of potassium but depressed respiration in the presence of low levels of calcium. Calcium improved respiration of washed spermatozoa and caused the accumulation of lactate without any concomitant increase in fructose utilization. Washing the spermatozoa free of their seminal plasma reduced the oxidation of substrates other than fructose. This effect was probably due to the removal of alternative substrates in the seminal plasma. The lactate present in dog semen only accounted for a small proportion of oxygen uptake and other alternative substrates are discussed.

Influence of some mononucleotides and their corresponding nucleosides on the metabolism of carbohydrates in the isolated rat diaphragm muscle

1. The influence of ATP on glucose metabolism was studied in the isolated rat diaphragm; it was shown that ATP increases the oxidation of glucose and the aerobic conversion of glucose into lactate, whereas it decreases glycogen synthesis. There was no influence of ATP on the anaerobic formation of lactate from glucose. 2. A maximum effect of ATP on the oxidation of glucose (about 160% increase) was obtained in the presence of 10mm-ATP; in the presence of 2mm-ATP the effect was about 65%, and was approximately constant from 10 to 90min. incubation period. 3. In a phosphate-free tris-buffered medium the oxidation of glucose was considerably decreased, but the percentage stimulation by ATP was about the same as in a phosphate-buffered medium. 4. ATP was shown to increase the oxidation of fructose, glucose 6-phosphate, glucose 1-phosphate, fructose 1,6-diphosphate and, to a much smaller extent, pyruvate. 5. ADP stimulated the oxidation of glucose to the same extent as ATP at a concentration of 2mm and the effect with AMP was only slightly less; IMP and adenosine had only a small stimulatory effect at this concentration, whereas inosine had no effect.

EFFECTS OF DILUENT COMPOSITION ON THE METABOLISM OF BULL, DOG, RABBIT AND FOWL SPERMATOZOA.

Summary. A study has been made of the effects of potassium, magnesium, calcium and phosphate ions and their possible inter-relationships on the metabolism of bull, dog, rabbit and fowl spermatozoa. Respiration and fructolysis were measured and isotopically labelled fructose used to assess the contribution of fructose oxidation to total oxygen uptake. Overall, fowl spermatozoa had the lowest rate of metabolism. Dog spermatozoa had the greatest respiratory activity and differences in oxygen uptake between the mammalian species were due mainly to variations in the rate of fructose oxidation. Washing bull, dog and rabbit spermatozoa greatly reduced the oxidation of substrates other than fructose, but washing had little effect in the fowl. In general, phosphate ions depressed the respiration of bull spermatozoa, but stimulated their aerobic fructolysis. Except for stimulating the respiration of unwashed dog spermatozoa, phosphate had no important influence on metabolism in the other species. Potassium stimulated some aspects of metabolism in all species, but had its greatest effect upon the respiration of dog spermatozoa. Magnesium depressed the respiration of bull and fowl spermatozoa, but calcium was without effect. There were few significant interactions between the ions tested.