Some effects of mannitol on the glucose metabolism of two derivatives of a strain ofRhizobium japonicum differing in mannitol dehydrogenase

The effects of mannitol were investigated by comparing some metabolic features in colonial derivatives, I-110 and L1-110, ofRhizobium japonicum strain 3IIb110, grown either on glucose alone (G-cells) or in glucose media supplemented with mannitol (GM-cells). The polyol stimulated the synthesis of not only mannitol dehydrogenase, which is active in derivative L1-110, but also the nicotinamide adenine dinucleotide (NAD)-linked 6-phosphogluconate (6-PG) dehydrogenase (EC 1.1.1.43). As revealed by radiorespirometry, when GM-cells were allowed to metabolize glucose, they produced relatively more CO₂ from the first and sixth carbons of the sugar than G-cells did. This finding is evidence that NAD-linked 6-PG dehydrogenase might initiate an unknown pathway different from the hexose cycle and the pentose phosphate (PP) pathway. Mannitol exerted no allosteric control on the oxygen consumption and the glucose transport systems. Active uptake of the polyol was correlated with the presence of mannitol dehydrogenase (EC 1.1.1.67); it did not hinder the transport of glucose even though both systems derive their energy for active transport from a common source presumptively characterized as the energized membrane state. Mannitol, however, suppressed by two- or threefold the glucose uptake system. Addition of the polyol to the cell suspensions of both colonial types ofR. japonicum metabolizing glucose caused an immediate 40–50% drop of adenosine triphosphate (ATP) concentrations, owing in part to the mannitol kinase reaction. Type I-110 failed to overcome this reduction of ATP levels, and low growth rates could results. In contrast, type L1-110 offsets the reduction of ATP concentration by oxidizing mannitol as an additional source of energy through mannitol dehydrogenase, fructokinase, and a sequence of glycolytic reactions. The polyol also induced type L1-110 to produce extracellular slimy materials that, apparently, harbor amounts of ATP and proteins.     

Pathways of glucose metabolism in Candida 107, a lipid-accumulating yeast.

Phosphofructokinase was not detected in extracts of Candida 107 prepared in a variety of ways but was highly active in cells treated with toluene. Disruption of these cells destroyed activity of phosphofructokinase indicating that the enzyme is extremely labile. As patterns of labelling from [I-14C]glucose and [6-14C]glucose showed that 60% of glucose was metabolized via the pentose cycle, augmentation of this cycle is necessary to account for the high molar growth yields of this yeast. Phosphoketolases, reacting with xylulose 5-phosphate and fructose 6-phosphate, were found but the extent to which they contribute to glucose metabolism was not assessed.     

The effect of hyperosmotic mannitol and glucose on heart function.

In the dog heart-lung preparation the effects of glucose and mannitol induced hyperosmolality were examined on left ventricular water content, ventricular compliance, cardiac performance, and coronary blood flow. Glucose-induced increase of serum osmolality by more than 20% resulted in a decrease of myocardial water content and an increase of left ventricular diastolic stiffness if insulin was absent, but the changes did not develop if it was present. Insulin failed to prevent the alterations if hyperosmolality was induced with the nonmetabolizable sugar, mannitol. Coronary blood flow increased in each type of experiments. It is concluded that diagnostic and clinical treatment with hyperosmotic solutions of nonmetabolizable agents can account for disturbed left ventricular compliance and decreased cardiac performance, as it may occur in hyperosmolar diabetic coma.     

Fermentation of glucose, lactose, galactose, mannitol, and xylose by bifidobacteria

For six strains of Bifidobacterium bifidum (Lactobacillus bifidus), fermentation balances of glucose, lactose, galactose, mannitol, and xylose were determined. Products formed were acetate, l(+)-lactate, ethyl alcohol, and formate. l(+)-Lactate dehydrogenase of all strains studied was found to have an absolute requirement for fructose-1,6-diphosphate. The phosphoroclastic enzyme could not be demonstrated in cell-free extracts. Cell suspensions fermented pyruvate to equimolar amounts of acetate and formate. Alcohol dehydrogenase was shown in cell-free extracts. Possible explanations have been suggested for the differences in fermentation balances found for different strains and carbon sources. By enzyme determinations, it was shown that bifidobacteria convert mannitol to fructose-6-phosphate by an inducible polyol dehydrogenase and fructokinase. For one strain of B. bifidum, molar growth yields of glucose, lactose, galactose, and mannitol were determined. The mean value of Y (ATP), calculated from molar growth yields and fermentation balances, was 11.3.     

Carbohydrate metabolism in pregnancy. Part II. Relation between maternal glucose tolerance and glucose metabolism in the newborn.

The objective of clinical management of the pregnant diabetic woman is to prevent the serious adverse effects of an abnormal glucose environment on the fetus. Neonatal glucose assimilation and insulin release over the first two hours of life were correlated with various indices of maternal carbohydrate metabolism in the third trimester. Of the 31 mothers studied 21 were defined as normal and 10 as having chemical diabetes. Neontal glucose assimilation during the first two hours of life correlated strongly with functions of both maternal glucose tolerance and mean diurnal glucose level, the strongest correlation being with the area under the three-hour oral glucose tolerance curve (P less than 0.001), Two-hour neonatal plasma glucose values of under 1.7 mmol/1 (30 mg/100 ml) were found only in the newborn of women whose glucose tolerance area measured over 41.6 area units (750 traditional units); thus, even in the borderline diabetic range glucose tolerance testing during the last trimester of pregnancy may be valuable in predicting likelihood of neonatal hypoglycaemia. The findings also shed light on the possible sensitizing role of mild maternal hyperglycaemia on fetal insulin production and secretion.     

Enzymes of glucose metabolism in Frankia sp.

Enzymes of glucose metabolism were assayed in crude cell extracts of Frankia strains HFPArI3 and HFPCcI2 as well as in isolated vesicle clusters from Alnus rubra root nodules. Activities of the Embden-Meyerhof-Parnas pathway enzymes glucokinase, phosphofructokinase, and pyruvate kinase were found in Frankia strain HFPArI3 and glucokinase and pyruvate kinase were found in Frankia strain HFPCcI2 and in the vesicle clusters. An NADP+-linked glucose 6-phosphate dehydrogenase and an NAD-linked 6-phosphogluconate dehydrogenase were found in all of the extracts, although the role of these enzymes is unclear. No NADP+-linked 6-phosphogluconate dehydrogenase was found. Both dehydrogenases were inhibited by adenosine 5-triphosphate, and the apparent Km's for glucose 6-phosphate and 6-phosphogluconate were 6.86 X 10(-4) and 7.0 X 10(-5) M, respectively. In addition to the enzymes mentioned above, an NADP+-linked malic enzyme was detected in the pure cultures but not in the vesicle clusters. In contrast, however, the vesicle clusters had activity of an NAD-linked malic enzyme. The possibility that this enzyme resulted from contamination from plant mitochondria trapped in the vesicle clusters could not be discounted. None of the extracts showed activities of the Entner-Doudoroff enzymes or the gluconate metabolism enzymes gluconate dehydrogenase or gluconokinase. Propionate- versus trehalose-grown cultures of strain HFPArI3 showed similar activities of most enzymes except malic enzyme, which was higher in the cultures grown on the organic acid. Nitrogen-fixing cultures of strain HFPArI3 showed higher specific activities of glucose 6-phosphate and 6-phosphogluconate dehydrogenases and phosphofructokinase than ammonia-grown cultures.     

Intracellular metabolism of 4-hydroxynonenal

4-hydroxynonenal (HNE) is a major aldehydic product of lipid peroxidation known to exert a multitude of biological, cytotoxic, and signal effects. Mammalian cells possess highly active pathways of HNE metabolism. The metabolic fate of HNE was investigated in various mammalian cells and organs such as hepatocytes, intestinal enterocytes, renal tubular cells, aortic and brain endothelial cells, synovial fibroblasts, neutrophils, thymocytes, heart, and tumor cells. The experiments were carried out at 37 degrees C at initial HNE concentrations between 1 microM--that means in the range of physiological and pathophysiologically relevant HNE levels--to 100 microM. In all cell types which were investigated, 90-95% of 100 microM HNE were degraded within 3 min of incubation. At 1 microM HNE the physiological blood serum level of about 0.1-0.2 microM was restored already after 10-30 s. As primary products of HNE in hepatocytes and other cell types the glutathione-HNE-1:1-conjugate, the hydroxynonenoic acid and the corresponding alcohol of HNE, the 1,4-dihydroxynonene, were identified. Furthermore, the beta-oxidation of hydroxynonenoic acid including the formation of water was demonstrated. The quantitative share of HNE binding to proteins was low with about 2-8% of total HNE consumption. The glycine-cysteine-HNE, cysteine-HNE adducts and the mercapturic acid from glutathione-HNE adduct were not formed in the most cell types, but in kidney cells and neutrophils. The rapid metabolism underlines the role of HNE degrading pathways in mammalian cells as important part of the secondary antioxidative defense mechanisms in order to protect proteins from modification by aldehydic lipid peroxidation products.     

Intracellular characterization of aerobic glucose metabolism in seven yeast species by 13C flux analysis and metabolomics

Key distinguishing characteristics of yeast glucose metabolism are the relative proportions of fermentation and respiration. Crabtree-positive yeast species exhibit a respirofermentative metabolism, whereas aerobic species respire fully without secretion of fermentation byproducts. Physiological data suggest a gradual transition in different species between these two states. Here, we investigate whether this gradual transition also occurs at the intracellular level by quantifying the intracellular metabolism of Saccharomyces cerevisiae, Saccharomyces bayanus, Saccharomyces exiguus, Kluyveromyces thermotolerans, Yarrowia lipolytica, Pichia angusta and Candida rugosa by (13)C-flux analysis and metabolomics. Different from the extracellular physiology, the intracellular fluxes through the tricarboxylic acid cycle fall into two classes where the aerobic species exhibit much higher respiratory fluxes at otherwise similar glycolytic fluxes. More generally, we found the intracellular metabolite concentrations to be primarily species-specific. The sole exception of a metabolite-flux correlation in a species-overarching manner was found for fructose-1,6-bisphosphate and dihydroxyacetone-phosphate, indicating a conservation of the functional properties around these two metabolites.     

Intracellular metalloporphyrin metabolism in Staphylococcus aureus

The bacterial pathogen Staphylococcus aureus is responsible for a significant amount of human morbidity and mortality, and the ability of S. aureus to cause disease is absolutely dependent on the acquisition of iron from the host. The most abundant iron source to invading staphylococci is in the form of the porphyrin heme. S. aureus is capable of acquiring nutrient iron from heme and hemoproteins via two heme-acquisition systems, the iron-regulated surface determinant system (Isd) and the heme transport system (Hts). Heme acquisition through these systems is involved in staphylococcal pathogenesis suggesting that the intracellular fate of heme plays a significant role in the infectious process. The valuable heme molecule presents a paradox to invading bacteria because although heme is an abundant source of nutrient iron, the extreme reactivity of heme makes it toxic at high concentrations. Therefore, bacteria must regulate the levels of intracellular heme to avoid toxicity. Although the molecular mechanisms responsible for staphylococcal heme acquisition are beginning to emerge, the mechanisms by which S. aureus regulate intracellular heme homeostasis are largely unknown. In this review we describe three potential fates of host-derived heme acquired by S. aureus during infection: (i) degradation for use as a nutrient iron source, (ii) incorporation into bacterial heme-binding proteins for use as an enzyme cofactor, or (iii) efflux through a dedicated ABC-type transport system. We hypothesize that the ultimate fate of exogenously acquired heme in S. aureus is dependent upon the intracellular and extracellular availability of both iron and heme.     

Intracellular metabolism of triglyceride-rich lipoproteins

Over the past 10 years, many advances have been made in our understanding of the intravascular metabolism of triglyceride-rich lipoproteins. It is now known that the complex extracellular interactions of triglyceride-rich lipoprotein-associated apolipoprotein E, lipoprotein lipase and hepatic lipase with heparan sulfate proteoglycans and lipoprotein receptors facilitate the hepatocellular uptake of triglyceride-rich lipoproteins. Recent studies have also revealed that the intracellular fate of internalized triglyceride-rich lipoproteins is highly complex. The dissociation of triglyceride-rich lipoprotein components within intracellular endosomal compartments involves the recycling of apolipoprotein E, whereas the remaining lipid core associated with apolipoprotein B is susceptible to lysosomal degradation. Apolipoprotein E recycling is an important newly discovered feature of lipoprotein metabolism, and will be discussed in the context of its intracellular transport mechanisms and cholesterol efflux. Current concepts concerning its potential relevance with regard to lipoprotein metabolism and atherosclerosis will also be discussed.     

Disorders of glucose metabolism in sleep apnea.

Sleep is a complex behavioral state that occupies one-third of the human life span. Although viewed as a passive condition, sleep is a highly active and dynamic process. The sleep-related decrease in muscle tone is associated with an increase in resistance to airflow through the upper airway. Partial or complete collapse of the airway during sleep can lead to the occurrence of apneas and hypopneas during sleep that define the syndrome of sleep apnea. Sleep apnea has become pervasive in Western society, affecting approximately 5% of adults in industrialized countries. Given the pandemic of obesity, the prevalence of Type 2 diabetes mellitus and metabolic syndrome has also increased dramatically over the last decade. Although the role of sleep apnea in cardiovascular disease is uncertain, there is a growing body of literature that implicates sleep apnea in the pathogenesis of altered glucose metabolism. Intermittent hypoxemia and sleep fragmentation in sleep apnea can trigger a cascade of pathophysiological events, including autonomic activation, alterations in neuroendocrine function, and release of potent proinflammatory mediators such as tumor necrosis factor-alpha and interleukin-6. Epidemiologic and experimental evidence linking sleep apnea and disorders of glucose metabolism is reviewed and discussed here. Although the cause-and-effect relationship remains to be determined, the available data suggest that sleep apnea is independently associated with altered glucose metabolism and may predispose to the eventual development of Type 2 diabetes mellitus.