Adaption to High Altitude: An Evaluation of the Storage Quality of Suspended Red Blood Cells Prepared from the Whole Blood of Tibetan Plateau Migrants

Hypoxia has been reported to cause the significant enhancement of hemoglobin (Hb) and hematocrit (Hct), which stabilizes at relatively high levels after an individual ascends to a high altitude. However, the quality of the suspended red blood cells (SRBCs) obtained from individuals at high altitudes such as Tibetan plateau migrants after storage has not been studied. In this study, we compared the storage quality of SRBCs prepared from Tibetan plateau and Deyang lowland populations by adding a normal volume of mannitol-adenine-phosphate (MAP), which is a common additive solution used in blood storage in Asian countries. The storage cell characteristics were examined on days1, 7, 14 and 35.We found higher Hct and Hb levels and viscosity in the high altitude samples. The metabolic rates, including those for electrolytes and lactate, were higher in plateau SRBCs than in lowland SRBCs; these findings were consistent with the higher osmotic fragility and hemolysis of plateau SRBCs throughout the entire storage period. In addition, the reduction rates of 2,3-diphosphoglycerate (2,3-DPG) and oxygen tension to attain 50% oxygen saturation of Hb (P50) in plateau SRBCs were higher than those in lowland SRBCs, and the oxygen delivering capacity in plateau SRBCs was weaker than that in lowland SRBCs. We concluded that the storage quality of plateau SRBCs was inferior to that of lowland SRBCs when using the same concentration of MAP. We suggested that the optimal formula, including the MAP concentration or even a new additive solution, to store the plateau SRBCs must be assessed and regulated.

Effect of oxygen on glucose metabolism: utilization of lactate in Staphylococcus aureus as revealed by in vivo NMR studies

The ability to successfully adapt to changing host conditions is crucial for full virulence of bacterial pathogens. Staphylococcus aureus has to cope with fluctuating oxygen concentrations during the course of infection. Hence, we studied the effect of oxygen on glucose metabolism in non-growing S. aureus COL-S cells by in vivo¹³C-NMR. Glucose catabolism was probed at different oxygen concentrations in suspensions of cells grown aerobically (direct effects on metabolism) or anaerobically (transcriptional adjustment to oxygen deprivation). In aerobically-grown cells, the rate of glucose consumption diminished progressively with decreasing oxygen concentrations. Additionally, oxygen deprivation resulted in biphasic glucose consumption, with the second phase presenting a higher rate. The fructose-1,6-bisphosphate pool peaked while glucose was still abundant, but the transient maximum varied with the oxygen concentration. As oxygen became limiting mannitol/mannitol-1-phosphate were detected as products of glucose catabolism. Under anoxic conditions, accumulation of mannitol-1-phosphate ceased with the switch to higher glucose consumption rates, which implies the activation of a more efficient means by which NAD⁺ can be regenerated. The distribution of end-products deriving from glucose catabolism was dramatically affected by oxygen: acetate increased and lactate decreased with the oxygen concentration; ethanol was formed only anaerobically. Moreover, oxygen promoted the energetically favourable conversion of lactate into acetate, which was particularly noticeable under fully oxygenated conditions. Interestingly, under aerobiosis growing S. aureus cells also converted lactate to acetate, used simultaneously glucose and lactate as substrates for growth, and grew considerably well on lactate-medium. We propose that the efficient lactate catabolism may endow S. aureus with a metabolic advantage in its ecological niche.

Mannitol 1-phosphate metabolism is required for sporulation in planta of the wheat pathogen Stagonospora nodorum

An expressed sequence tag encoding a putative mannitol 1-phosphate dehydrogenase (Mpd1) has been characterized from the fungal wheat pathogen Stagonospora nodorum. Mpd1 was disrupted by insertional mutagenesis, and the resulting mpd1 strains lacked all detectable NAD-linked mannitol 1-phosphate dehydrogenase activity (EC 1.1.1.17). The growth rates, sporulation, and spore viability of the mutant strains in vitro were not significantly different from the wild type. The viability of the mpd1 spores when subjected to heat stress was comparable to wild type. Characterization of the sugar alcohol content by nuclear magnetic resonance spectroscopy revealed that, when grown on glucose, the mutant strains contained significantly less mannitol, less arabitol, but more trehalose than the wild-type strains. The mannitol content of fructose-grown cultures was normal. No secreted mannitol could be detected in wild type or mutants. Pathogenicity assays revealed the disruption of Mpd1 did not affect lesion development, however the mutants were unable to sporulate. These results throw new light on the role of mannitol in fungal plant interactions, suggesting a role in metabolic and redox regulation during the critical process of sporulation on senescing leaf material.

Purification and characterization of an acid phosphatase from the commercial mushroom Agaricus bisporus

Acid phosphatase [AP; EC 3.1.3.2], a key enzyme involved in the synthesis of mannitol in Agaricus bisporus, was purified to homogeneity and characterized. The native enzyme appeared to be a high molecular weight type glycoprotein. It has a molecular weight of 145 kDa and consists of four identical 39-kDa subunits. The isoelectric point of the enzyme was found at 4.7. Maximum activity occurred at 65 degrees C. The optimum pH range was between 3.5 and 5.5, with maximum activity at pH 4.75. The enzyme was unaffected by EDTA, and inhibited by tartrate and inorganic phosphate. The enzyme exhibits a Km for p-nitrophenylphosphate and fructose-6-phosphate of 370 microM and 3.1 mM, respectively. A broad substrate specificity was observed with significant activities for fructose-6-phosphate, glucose-6-phosphate, mannitol-1-phosphate, AMP and beta-glycerol phosphate. Only phosphomonoesters were dephosphorylated. Antibodies raised against the purified enzyme could precipitate AP activity from a cell-free extract in an anticatalytic immunoprecipitation test.

Metabolic characterization of Lactococcus lactis deficient in lactate dehydrogenase using in vivo 13C-NMR

The metabolism of glucose by nongrowing cells of Lactococcus lactis strain FI7851, constructed from the wild-type L. lactis strain MG1363 by disruption of the lactate dehydrogenase (ldh) gene [Gasson, M.J., Benson, K., Swindel, S. & Griffin, H. (1996) Lait 76, 33-40] was studied in a noninvasive manner by 13C-NMR. The kinetics of the build-up and consumption of the pools of intracellular intermediates mannitol 1-phosphate, fructose 1,6-bisphosphate, 3-phosphoglycerate, and phosphoenolpyruvate as well as the utilization of [1-13C]glucose and formation of products (lactate, acetate, mannitol, ethanol, acetoin, 2,3-butanediol) were monitored in vivo with a time resolution of 30 s. The metabolism of glucose by the parental wild-type strain was also examined for comparison. A clear shift from typical homolactic fermentation (parental strain) to a mixed acid fermentation (lactate dehdydrogenase deficient; LDHd strain) was observed. Furthermore, high levels of mannitol were transiently produced and metabolized once glucose was depleted. Mannitol 1-phosphate accumulated intracellularly up to 76 mM concentration. Mannitol was formed from fructose 6-phosphate by the combined action of mannitol-1-phosphate dehydrogenase and phosphatase. The results show that the formation of mannitol 1-phosphate by the LDHd strain during glucose catabolism is a consequence of impairment in NADH oxidation caused by a highly reduced LDH activity, the transient production of mannitol 1-phosphate serving as a regeneration pathway for NAD+ regeneration. Oxygen availability caused a drastic change in the pattern of intermediates and end-products, reinforcing the key-role of the fulfilment of the redox balance. The flux control coefficients for the step catalysed by mannitol-1-phosphate dehydrogenase were calculated and the implications in the design of metabolic engineering strategies are discussed.

Mannitol 1-phosphate mediates an inhibitory effect of mannitol on the activity and the translocation of glucokinase in isolated rat hepatocytes

When tested in the presence of an inhibitor of sorbitol dehydrogenase, both mannitol and sorbitol caused a progressive inhibition of the detritiation of [2-3H]glucose in isolated rat hepatocytes. The purpose of the present work was to investigate the possibility that this effect was mediated by the regulatory protein of glucokinase. When added to hepatocytes, mannitol decreased the apparent affinity of glucokinase for glucose and increased the concentration of fructose required to stimulate detritiation, without affecting the concentration of fructose 1-phosphate. Its effect could be attributed to the formation of mannitol 1-phosphate, a potent agonist of the regulatory protein, which, similarly to fructose 6-phosphate, reinforces its inhibitory action. Formation of mannitol 1-phosphate in hepatocytes was dependent on the presence of mannitol and was stimulated by compounds that increase the concentration of glucose 6-phosphate. Liver extracts catalysed the conversion of mannitol to mannitol 1-phosphate about 7 times more rapidly in the presence of glucose 6-phosphate than of ATP. The glucose 6-phosphate-dependent formation was entirely accounted for by a microsomal enzyme, glucose-6-phosphatase and was not due to a loss of latency of this enzyme. In hepatocytes in primary culture, mannitol decreased the detritiation rate and counteracted the effect of fructose to stimulate glucokinase translocation. Taken together, these results strongly support a central role played by the regulatory protein in the control of glucokinase activity and translocation in the liver, as well as a feedback control exerted by fructose 6-phosphate on this enzyme.

HPr/HPr-P phosphoryl exchange reaction catalyzed by the mannitol specific enzyme II of the bacterial phosphotransferase system

The mannitol specific Enzyme II of the phosphoenolpyruvate: sugar phosphotransferase system of Escherichia coli catalyzes an exchange reaction in which a phosphoryl moiety is transferred from one molecule of the heat stable phosphocarrier protein HPr to another. An assay was developed for measuring this reaction. Unlabeled phospho-HPr and 125I-labeled free HPr were incubated together in the presence of Enzyme IImtl, and production of 125I-labeled phospho-HPr was measured. The reaction was concentration-dependent with respect to Enzyme IImtl and did not occur in its absence. The reaction occurred in the absence of Mg2+ in the presence of 10 mM EDTA. Treatment of Enzyme IImtl with the histidyl reagent diethylpyrocarbonate inactivated it with respect to the exchange reaction. Levels of N-ethylmaleimide which inactivate Enzyme IImtl with respect to both P-enolpyruvate-dependent phosphorylation of mannitol and mannitol/mannitol-1-P transphosphorylation did not affect its activity in the exchange reaction; however, treatment with another sulfhydryl reagent, p-chloromercuribenzoate, resulted in partial inactivation. The pH optimum for the Enzyme IImtl-catalyzed exchange reaction was about 7.5. Enzyme I and the glucose specific Enzyme III, two other E. coli phosphotransferase system proteins which, like Enzyme IImtl, interact directly with HPr, were also shown to catalyze 125I-HPr/HPr-P phosphoryl exchange.

Mannitol-1-phosphate dehydrogenase of Escherichia coli. Chemical properties and binding of substrates

Mannitol-1-phosphate dehydrogenase was purified to homogeneity, and some chemical and physical properties were examined. The isoelectric point is 4.19. Amino acid analysis and polyacrylamide-gel electrophoresis in presence of SDS indicate a subunit Mr of about 22,000, whereas gel filtration and electrophoresis of the native enzyme indicate an Mr of 45,000. Thus the enzyme is a dimer. Amino acid analysis showed cysteine, tyrosine, histidine and tryptophan to be present in low quantities, one, three, four and four residues per subunit respectively. The zinc content is not significant to activity. The enzyme is inactivated (greater than 99%) by reaction of 5,5'-dithiobis-(2-nitrobenzoate) with the single thiol group; the inactivation rate depends hyperbolically on reagent concentration, indicating non-covalent binding of the reagent before covalent modification. The pH-dependence indicated a pKa greater than 10.5 for the thiol group. Coenzymes (NAD+ and NADH) at saturating concentrations protect completely against reaction with 5,5'-dithiobis-(2-nitrobenzoate), and substrates (mannitol 1-phosphate, fructose 6-phosphate) protect strongly but not completely. These results suggest that the thiol group is near the catalytic site, and indicate that substrates as well as coenzymes bind to free enzyme. Dissociation constants were determined from these protective effects: 0.6 +/- 0.1 microM for NADH, 0.2 +/- 0.03 mM for NAD+, 9 +/- 3 microM for mannitol 1-phosphate, 0.06 +/- 0.03 mM for fructose 6-phosphate. The binding order for reaction thus may be random for mannitol 1-phosphate oxidation, though ordered for fructose 6-phosphate reduction. Coenzyme and substrate binding in the E X NADH-mannitol 1-phosphate complex is weaker than in the binary complexes, though in the E X NADH+-fructose 6-phosphate complex binding is stronger.

Kinetics and subunit interaction of the mannitol-specific enzyme II of the Escherichia coli phosphoenolpyruvate-dependent phosphotransferase system

Purified mannitol-specific enzyme II (EIImtl), in the presence of the detergent Lubrol, catalyzes the phosphorylation of mannitol from P-HPr via a classical ping-pong mechanism involving the participation of a phosphorylated EIImtl intermediate. This intermediate has been demonstrated by using radioactive phosphoenolpyruvate. Upon addition of mannitol, at least 80% of the enzyme-bound phosphoryl groups can be converted to mannitol 1-phosphate. The EIImtl concentration dependence of the exchange reaction indicates that self-association is a prerequisite for catalytic activity. The self-association can be achieved by increasing the EIImtl concentration or at low concentrations of EIImtl by adding HPr or bovine serum albumin. The equilibrium is shifted toward the dissociated form by mannitol 1-phosphate, resulting in a mannitol 1-phosphate induced inhibition. Mannitol does not affect the association state of the enzyme. Both mannitol and mannitol 1-phosphate also act as classical substrate inhibitors. The apparent Ki of each compound, however, is approximately equal to its apparent Km, suggesting that mannitol and mannitol 1-phosphate bind at the same site on EIImtl. Due to strong inhibition provided by mannitol and mannitol 1-phosphate in the exchange reaction, the kinetics of this reaction cannot be used to determine whether the reaction proceeds via a ping-pong or an ordered reaction mechanism.

Rapid turnover of mannitol-1-phosphate in Escherichia coli

The phosphate moiety of D-mannitol-1-phosphate in Escherichia coli is subject to rapid turnover and is in close equilibrium with Pi and the phosphorus of fructose-1,6-bisphosphate. These three compounds account for the bulk of 32P label found in cells after several minutes of uptake of 32Pi and mannitol-1-phosphate represents some 30% of this label. Mannitol-1-phosphate occurs in E. coli grown on a variety of carbon sources, in the absence of D-mannitol, and is synthesized de novo even in mutants lacking mannitol-1-phosphate dehydrogenase. The mannitol moiety of mannitol-1-phosphate was not affected during the total chase of the P moiety, which exchanged with a half-life of about 30 s. These findings suggest that the rapid equilibration of the phosphorus is a function of an enzyme, possibly a component of the phosphotransferase system, capable of forming a complex that allows the exchange of the phosphate without the equilibration of the mannitol moiety with free mannitol.

Conversion of D-mannitol to D-ribose: a newly discovered pathway in Escherichia coli

A mutant (mtlD) strain of Escherichia coli unable to oxidize mannitol-1-phosphate to fructose-6-phosphate was used to study the fate of mannitol-1-phosphate. D-[1-14C]mannitol entered the cells via the phosphotransferase system and was phosphorylated equally at carbon 1 or 6. The label disappeared gradually from the mannitol-1-phosphate pool, and some 60% of the 14C was recovered in nucleic acids. Ribose was isolated from the purified RNA. The 14C label distribution in the isolated ribose precluded a simple hexose-to-pentose conversion by elimination of one terminal carbon from mannitol-1-phosphate. The 14C from mannitol-1-phosphate that did not enter macromolecules was found in CO2 and in some organic, non-phosphorylated compounds that were not identified. We suggest that the de novo synthesis of mannitol-1-phosphate in E. coli may be a reaction specifically dedicated to the biosynthesis of ribose.

Mannitol-specific enzyme II of the bacterial phosphotransferase system. II. Reconstitution of vectorial transphosphorylation in phospholipid vesicles

Purified mannitol Enzyme II from Escherichia coli was reconstituted in phospholipid vesicles employing the octylglucoside dilution procedure and was shown to catalyze vectorial mannitol 1-phosphate:mannitol transphosphorylation. Reconstitution of the enzyme into liposomes showed a marked dependency upon the octylglucoside concentration with an optimum at 1.2%. The reconstituted transphosphorylation activity exhibited an absolute dependence upon mannitol 1-phosphate as the phosphoryl donor, was sensitive to N-ethylmaleimide, and had a pH optimum near 6. The intravesicular radiolabeled mannitol phosphate could be released from the proteoliposomes by the addition of either 50 microM unlabeled mannitol or 0.5% sodium dodecyl sulfate. The rate of formation of intraliposomal mannitol phosphate, measured as a function of the mannitol Enzyme II concentration, showed a sigmoidal response, suggesting that at high enzyme concentrations the mannitol Enzyme II exists in an aggregated or oligomeric state and that this form is more active than the monomeric or dissociated form of the enzyme in catalyzing the vectorial mannitol transphosphorylation reaction.

Intracellular mannitol, a product of glucose metabolism in staphylococci

Mannitol (Mtl), not previously reported as an intracellular component of bacteria, although it has been found as an extracellular end product of anaerobic carbohydrate metabolism, accumulated within strains of all 10 staphylococcal species tested after aerobic incubation of washed cell suspensions in phosphate-buffered 1% glucose for 2 h. Phenol extracts of the cells, before and after incubation, were analyzed for Mtl content by periodate utilization and paper chromatography and for Mtl 1-phosphate content, with Mtl 1-phosphate dehydrogenase. In Staphylococcus aureus Towler, the content of Mtl increased from a 0-h value of less than 2.4 to 16 mumol/g (dry weight) after incubation, and the level of Mtl 1-phosphate increased from a 0-h value of 1 to 8 mumol/g. The identification of Mtl was confirmed as the per-O-acetyl ester by gas-liquid chromatography and as the per-O-methyl ether by mass spectrometry. Also tested were 5 additional S. aureus strains and 32 coagulase-negative staphylococcal strains. All strains accumulated Mtl, even those strains that could not utilize exogenous Mtl during aerobic growth, usually in the range 4 to 25 mumol/g. Furthermore, three strains accumulated very high Mtl levels. Bacteria from several other genera were tested, and some were found to accumulate low to moderate levels of Mtl under similar incubation conditions. The metabolic conversion of glucose to intracellular Mtl, probably via Mtl 1-phosphate, is a common feature of staphylococci and also occurs in some other bacteria.

Genetic dissection of catalytic activities of the Salmonella typhimurium mannitol enzyme II

Approximately 60 mutants of Salmonella typhimurium were isolated which exhibited altered levels of the activities of the mannitol enzyme II. The mutants were grouped into six distinct categories based on their mannitol fermentation, transport, chemotaxis, and phosphorylation activities.

The distribution of the NADPH regenerating mannitol cycle among fungal species

The mannitol cycle is an important NADPH regenerating system in Alternaria alternata. The cycle is built up to the following enzymes: mannitol 1-phosphate dehydrogenase, mannitol 1-phosphatase, mannitol dehydrogenase and hexokinase. The net reaction of one cycle turn is: NADH + NADP+ + ATP leads to NAD+ + NADPH + ADP + Pi. The enzymes needed for an operating cycle were found in Aspergillus, Botrytis, Penicillium, Pyricularia, Trichothecium, Cladosporium and Thermomyces all genera belonging to Fungi Imperfecti. The only genus of this class lacking the cycle was Candida. No genera from the classes Basidiomycetes and Phycomycetes showed any mannitol 1-phosphate dehydrogenase or mannitol 1-phosphatase activities. The genera investigated, belonging to Ascomycetes, Gibberella, Ceratocystis and Neurospora all lacked mannitol 1-phosphate dehydrogenase. It was concluded that the mannitol cycle is an important and widespread pathway for NADH oxidation and NADP+ reduction in the organisms belonging to the class Fungi Imperfecti.