Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:2.7.1.1 (hexokinase)
5,274 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The enzymes mannitol-1-phosphate dehydrogenase, mannitol-1-phosphatase, mannitol dehydrogenase and hexokinase participate in an enzymatic cycle in the fungus Alternaria alternata. One turn of the cycle gives the net result: NADH + NADP+ + ATP leads to NAD+ + NADPH + ADP + Pi. The cycle alone can meet the total need of NADPH formation for fat synthesis in the organism. A polyketide producing strain of A. alternata shows a lower mannitol oxidation as well as a lower fat synthesis than a nonproducing mutant, supporting the hypothesis that polyketide formation is favoured at limiting NADPH production. It is further suggested that the mannitol cycle is regulating the glycolytic flux by substrate withdrawal from phosphofructokinase.
...
PMID:Production of NADPH in the mannitol cycle and its relation to polyketide formation in Alternaria alternata. 2 47

Recently, it was found that large quantities of mannitol are present in unsporulated oocysts of the protozoan parasite Eimeria tenella and that these levels diminish during maturation (sporulation). Investigations into the metabolic role of mannitol have led to the discovery that a mannitol cycle is present in this parasite. Prior to these studies the mannitol cycle was found exclusively in fungi. The parasite cycle is similar to that in the fungi although there are distinct differences in coenzyme requirements. The enzymes involved in the parasite pathway include mannitol-1-phosphate dehydrogenase (EC 1.1.1.17), mannitol-1-phosphatase (EC 3.1.3.22), mannitol dehydrogenase (EC 1.1.1.67), and hexokinase (EC 2.7.1.1). Kinetic studies were conducted to determine the Km and specific activities of these enzymes at both ambient temperature (where sporulation occurs) and the chicken's body temperature (41 degrees C). The data suggest that mannitol is produced during oocyst formation in the chicken gut and accumulated as an energy reserve for sporulation. The apparent lack of mannitol kinase in the organism and the Km values for the dehydrogenases in the reverse direction all indicate that the cycle only proceeds in one direction. In addition to serving as an energy storage system the cycle may also function as an electron 'sink' for the parasite which must survive in the anaerobic environment of the gut.
...
PMID:Evidence for and characterization of a mannitol cycle in Eimeria tenella. 253 47

A cyclic pathway of NADPH generation involving interconversion of mannitol and fructose has been proposed to occur in fungi. In Aspergillus nidulans three enzymes of this proposed mannitol cycle (hexokinase, NADP-mannitol dehydrogenase and mannitol-l-phosphate phosphatase) were shown to be localized exclusively in the cytosol. Two isoenzymes of the fourth enzyme (mannitol-l-phosphate dehydrogenase) were detected and shown to be localized respectively in the mitochondrion and the cytosol. The mitochondrial isoenzyme appeared to be present on the outer face of the inner mitochondrial membrane. No evidence was found for a coordinated change in the maximal activities of the enzymes of the proposed mannitol cycle in extracts prepared from mycelia grown on six different carbon, and three different nitrogen sources nor for any increase in these activities induced by growth on NO3-. Studies of this type in which other NADP-linked dehydrogenases were measured showed that for most carbon sources tested growth on NO3- increased the maximal activity of NADP-isocitrate dehydrogenase as well as that of glucose-6-phosphate and 6-phosphogluconate dehydrogenases but had little effect on the maximal activity of NADP-malate dehydrogenase (decarboxylating). Our studies provide no support for the operation of the mannitol cycle, or for the proposed role of this cycle in NADPH generation in A. nidulans.
...
PMID:NADPH generation in Aspergillus nidulans: is the mannitol cycle involved? 314 71

Pathways of mannitol biosynthesis and utilization in Aspergillus candidus NRRL 305 were studied in cell-free extracts of washed mycelia prepared by sonic and French pressure cell treatments. A nicotinamide adenine dinucleotide-linked mannitol-1-phosphate (M1P) dehydrogenase was found in French pressure cell extracts of d-glucose-grown cells, whereas a specific mannitol-1-phosphatase was present in extracts prepared by both methods. The existence of these two enzymes indicated that mannitol may be synthesized in this organism by the reduction of fructose-6-phosphate. A specific nicotinamide adenine dinucleotide phosphate-linked mannitol dehydrogenase was also identified in both extracts. This enzyme may have been involved in mannitol utilization. However, the level of the mannitol dehydrogenase appeared to be substantially reduced in extracts from mannitol-grown cells, whereas the level of M1P dehydrogenase was increased. A hexokinase has been identified in this organism. Fructose-6-phosphatase, glucose isomerase, and mannitol kinase could not be demonstrated.
...
PMID:D-mannitol metabolism by Aspergillus candidus. 430 50

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.
...
PMID:The distribution of the NADPH regenerating mannitol cycle among fungal species. 678 99

Three strains of Agaricus bisporus (B430, 116, and 155.8), which share the ability to form hyphal aggregates on solid media under axenic conditions, were investigated with respect to carbohydrate levels and activities of enzymes involved in their carbon metabolism. The size and macroscopic appearance of the aggregates, when grown on diluted medium, suggest that substrate limitation plays a role in the process of fruiting body development in A. bisporus. The enzymes trehalose phosphorylase (TP), mannitol dehydrogenase (MD), and glucose-6-phosphate dehydrogenase (G6PD) seem to be developmentally regulated, in contrast to hexokinase (HK). Activities of TP (measured in the direction of trehalose degradation), MD, and G6PD were higher in the hyphal aggregates compared with the mycelium, whereas HK activity varied little. In the period preceding the axenic formation of hyphal aggregates, synthesis of trehalose by TP approximately doubled in the mycelium. The carbohydrate levels, which were measured by HPLC, varied in a way similar to their corresponding enzymes. The results indicate synthesis of trehalose in the mycelium of A. bisporus before the hyphal aggregates arise. Subsequently, translocation of the trehalose takes place from the mycelium to the emerging aggregates. In these small aggregates the trehalose is rapidly broken down to yield glucose and glucose-1-phosphate, serving as carbon and energy sources for further growth of the aggregates and for the synthesis of the osmolyte mannitol.
...
PMID:Trehalose phosphorylase activity and carbohydrate levels during axenic fruiting in three Agaricus bisporus strains. 1048 56

Enzymes were investigated for their occurrence in the cell wall fraction (4,000 g sediment of the homogenate) of Agaricus bisporus sporocarps. Besides the markers malate dehydrogenase (MalDH), hexokinase (HK) and ATPase, the range of entities studied included gamma-glutamyl transferase (gamma-GT), mannitol dehydrogenase (MDH), phenoloxidase, chitin and beta-1,3-glucan synthases (ChS, beta-GS), chitinase, beta-N-acetylhexosaminidase (HexNAc'ase) and beta-glucanase. Using the extractability in dilute buffer, digitonin and NaCl at high ionic strength as the operational criteria, four categories (I-IV) of enzyme-wall associations could be discerned: category I encompasses enzymes which are artefactually present (i.e. contaminants); category II, enzymes that are hydrophobically bound (which may or may not be genuinely wall-associated), III includes enzymes that are ionically bound and IV, enzymes whose bonding to the wall is in all probability covalent. The same enzyme entity may have representatives in more than one category, e.g. ChS and beta-GS (I, II, IV), phenolase (I, II, III, IV), beta-glucanase, chitinase and HexNAc'ase (I, IV). It is thought that the categorization presented could be of general applicability in fungi as well as in higher plants to specify enzyme-wall associations in a straightforward, comparable manner, thus avoiding some of the ambiguous terms prevailing in the literature, such as "weakly", "strongly" or "tightly" wall bound. The results are discussed in more detail for several of the more economically important enzymes studied.
...
PMID:A system of categorizing enzyme-cell wall associations in Agaricus bisporus, using operational criteria. 1160 7

Of the growing list of promising genes for plant improvement, some of the most versatile appear to be those involved in sugar alcohol metabolism. Mannitol, one of the best characterized sugar alcohols, is a significant photosynthetic product in many higher plants. The roles of mannitol as both a metabolite and an osmoprotectant in celery (Apium graveolens) are well documented. However, there is growing evidence that 'metabolites' can also have key roles in other environmental and developmental responses in plants. For instance, in addition to its other properties, mannitol is an antioxidant and may have significant roles in plant-pathogen interactions. The mannitol catabolic enzyme mannitol dehydrogenase (MTD) is a prime modulator of mannitol accumulation in plants. Because the complex regulation of MTD is central to the balanced integration of mannitol metabolism in celery, its study is crucial in clarifying the physiological role(s) of mannitol metabolism in environmental and metabolic responses. In this study we used transformed Arabidopsis to analyze the multiple environmental and metabolic responses of the Mtd promoter. Our data show that all previously described changes in Mtd RNA accumulation in celery cells mirrored changes in Mtd transcription in Arabidopsis. These include up-regulation by salicylic acid, hexokinase-mediated sugar down-regulation, and down-regulation by salt, osmotic stress and ABA. In contrast, the massive up-regulation of Mtd expression in the vascular tissues of salt-stressed Arabidopsis roots suggests a possible role for MTD in mannitol translocation and unloading and its interrelation with sugar metabolism.
...
PMID:Analysis of celery (Apium graveolens) mannitol dehydrogenase (Mtd) promoter regulation in Arabidopsis suggests roles for MTD in key environmental and metabolic responses. 1172 47

Mannitol metabolism was evaluated in fruiting bodies of Lentinus edodes. Cell extracts were prepared from fruiting bodies, and key enzymes involved in mannitol metabolism were assayed, including hexokinase, mannitol dehydrogenase, mannitol-1-phosphate dehydrogenase, mannitol-1-phosphatase, and fructose-6-phosphatase. Mannitol dehydrogenase, fructose-6-phosphatase, mannitol-1-phosphatase, and hexokinase activities were found in extracts of fruiting bodies. However, mannitol-1-phosphate dehydrogenase activity was not detected. Mycelial cultures were grown in an enriched liquid medium, and enzymes of the mannitol cycle were assayed in cell extracts of rapidly growing cells. Mannitol-1-phosphate dehydrogenase activity was also not found in mycelial extracts. Hence, evidence for a complete mannitol cycle both in vegetative mycelia and during mushroom development was lacking. The pathway of mannitol synthesis in L. edodes appears to utilize fructose as an intermediate.
...
PMID:Mannitol Metabolism in Lentinus edodes, the Shiitake Mushroom. 1634 99

The sugar alcohol mannitol is an important carbohydrate with well-documented roles in both metabolism and osmoprotection in many plants and fungi. In addition to these traditionally recognized roles, mannitol is reported to be an antioxidant and as such may play a role in host-pathogen interactions. Current research suggests that pathogenic fungi can secrete mannitol into the apoplast to suppress reactive oxygen-mediated host defenses. Immunoelectron microscopy, immunoblot, and biochemical data reported here show that the normally symplastic plant enzyme, mannitol dehydrogenase (MTD), is secreted into the apoplast after treatment with the endogenous inducer of plant defense responses salicylic acid (SA). In contrast, a cytoplasmic marker protein, hexokinase, remained cytoplasmic after SA-treatment. Secreted MTD retained activity after export to the apoplast. Given that MTD converts mannitol to the sugar mannose, MTD secretion may be an important component of plant defense against mannitol-secreting fungal pathogens such as Alternaria. After SA treatment, MTD was not detected in the Golgi apparatus, and its SA-induced secretion was resistant to brefeldin A, an inhibitor of Golgi-mediated protein transport. Together with the absence of a known extracellular targeting sequence on the MTD protein, these data suggest that a plant's response to pathogen challenge may include secretion of selected defensive proteins by as yet uncharacterized, non-Golgi mechanisms.
...
PMID:Salicylic acid stimulates secretion of the normally symplastic enzyme mannitol dehydrogenase: a possible defense against mannitol-secreting fungal pathogens. 1992 7


1

---