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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Cell-fractionation and digitonin titration of procyclic trypomastigotes of Trypanosoma brucei, revealed that almost half of the total NADP+ -dependent glucose-6-phosphate dehydrogenase (G6PDH) activity, the first enzyme of the pentose phosphate pathway (PPP), is associated with glycosomes. The specific activity of G6PDH in the purified organelles was increased 4-fold relative to a total cell extract and showed latency. Moreover, in the absence of detergents this activity was totally resistant to the action of trypsin. The cytosolic counterpart was neither latent, nor was it resistant to trypsin. Both cytosolic and glycosomal G6PDH activities behaved identically on phenyl-, CM-, heparin-, and Affigel-blue-Sepharose columns. Both isoenzymes had a subunit Mr of 62 000 and an isoelectric point of 6.85, while kinetic studies carried out on the partially purified G6PDH from both cell compartments did not reveal any differences. The purified enzyme had an apparent Km of 138 and 5.3 microM for glucose 6-phosphate (G6P), and for NADP+, respectively, and had a specific activity of 14 micromol. (min mg of protein)(-1). We conclude that while in procyclic stages of T. brucei G6PDH activity is present in two different cell compartments, i.e. the cytosol and the glycosomes, these two activities most likely represent one and the same isoenzyme.
Mol Biochem Parasitol 1999 Mar 15
PMID:Purification, localisation and characterisation of glucose-6-phosphate dehydrogenase of Trypanosoma brucei. 1021 21

Chlamydia trachomatis is an obligate intracellular eubacteria that is dependent on a eukaryotic host cell for a variety of metabolites. For years, it has been speculated that chlamydiae are energy parasites, totally dependent on their host cell for ATP and other high-energy intermediates. To determine whether C. trachomatis contains functional enzymes that produce energy or reducing power, four enzymes involved in glycolysis or the pentose phosphate pathway, specifically pyruvate kinase, phosphoglycerate kinase, glyceraldehyde-3-phosphate dehydrogenase and glucose-6-phosphate dehydrogenase, were cloned, sequenced and expressed as recombinant proteins in Escherichia coli. The deduced amino acid sequences obtained show high homology to other pyruvate kinase, phosphoglycerate kinase, glyceraldehyde-3-phosphate dehydrogenase and glucose-6-phosphate dehydrogenase enzymes. In contrast to numerous other bacterial species, chlamydial glycolytic genes are not arranged in an operon, but are dispersed throughout the genome. Results from reverse transcriptase-polymerase chain reaction (RT-PCR) analysis indicate that all four genes are maximally expressed in the middle of the chlamydial developmental cycle. The chlamydial genes are capable of complementing mutant E. coli strains lacking the respective enzyme activities. In vitro enzyme analysis indicates that recombinant chlamydial enzymes expressed in E. coli are active and, interestingly, recombinant chlamydial pyruvate kinase is not regulated allosterically by fructose 1,6 bisphosphate or AMP, as found with other bacterial pyruvate kinases. In summary, identification and characterization of these glucose-catabolizing enzymes indicate that chlamydia contains the functional capacity to produce its own ATP and reducing power.
Mol Microbiol 1999 Jul
PMID:Glucose metabolism in Chlamydia trachomatis: the 'energy parasite' hypothesis revisited. 1041 34

In the light of recent findings on the effect of D-glucose upon D-fructose phosphorylation by human B-cell glucokinase, the influence of the aldohexose upon the metabolism of the ketohexose was investigated in rat pancreatic islets. D-glucose, although slightly decreasing D-[5-(3)H]fructose utilization, augmented the oxidation of the ketohexose, indicating that the aldohexose stimulates preferentially the oxidative, as distinct from anaerobic, modality of glycolysis. Such was not the case in parotid cells, taken as representative of functionally nonglucose-responsive cells. In the islets exposed to D-fructose, D-glucose also decreased the fractional contribution of the pentose shunt to the generation of CO2 and D-glyceraldehyde 3-phosphate from the ketohexose, and increased the inflow into the Krebs cycle of dicarboxylic metabolites relative to that of fructose-derived acetyl-CoA. This glucose-induced remodeling of D-fructose metabolism may optimize the insulin secretory response of islet cells to these hexoses, e.g. after food intake.
Mol Cell Biochem 1999 Jul
PMID:Hexose metabolism in pancreatic islets: effect of D-glucose upon D-fructose metabolism. 1048 41

To analyse genetic factors that potentially affect sugar quality and yield in Beta vulgaris, we designed primers based on 18 homologous ESTs and conserved regions of 32 heterologous ESTs encoding gene products that act in the Calvin cycle, the oxidative pentose phosphate cycle, photorespiration, synthesis, transport and degradation of sucrose, glycolysis, the citric acid cycle, nitrogen metabolism and osmoprotection. Data on the amplification of 54 gene homologues from B. vulgaris are presented. Among these are 35 homologues for which DNA sequence information from B. vulgaris is now available for the first time. For genetic mapping a PCR-based strategy using CAPS (cleaved amplified polymorphic sequence), DFLP (DNA fragment length polymorphism), SSCP (single-strand conformation polymorphism) and HD (heteroduplex) analysis was adopted. RFLP analysis was also used in some cases. The different techniques used for the detection of polymorphisms are evaluated with respect to their sensitivity and versatility. In all, 42 functional genes have been assigned to the nine linkage groups of sugar beet.
Mol Gen Genet 1999 Oct
PMID:PCR-based cloning and segregation analysis of functional gene homologues in Beta vulgaris. 1058 40

Activity of the pentose-phosphate pathway in several rat tissues was investigated, developing a new method that gives the activity of each phase (oxidative and non-oxidative) as well as the whole pathway separately. Our results demonstrate that this method is easy to carry out and that it has not the problems of indirect determinations of the previous ones. The activities of the oxidative and non-oxidative phases assayed separately gives us new information on the design of the pathway in the different tissues, from which several conclusions about the physiological role of this pathway can be derived. In all cases the activity of the oxidative phase was much higher than the non-oxidative one, and the global activity of the whole pathway was the same as the activity of the non-oxidative phase. The highest activity was found in lactating mammary gland and adipose tissue. Lung and liver showed to have a moderately high activity. Brain, kidney, skeletal muscle, and intestinal mucosa showed to have also a significant activity although less than other tissues. The switch in the mammary gland from the non-lactating state to the lactating one causes a very high increase of activity of 22 times, remaining the same ratio between the activity of the two phases.
Mol Cell Biochem 1999 Nov
PMID:Activity and metabolic roles of the pentose phosphate cycle in several rat tissues. 1063 Jun 23

Phosphoribulokinase (PRK), an enzyme unique to the reductive pentose phosphate pathway of CO2 assimilation, exhibits distinctive contrasting properties when the proteins from eukaryotic and prokaryotic sources are compared. The eukaryotic PRKs are typically dimers of -39 kDa subunits while the prokaryotic PRKs are octamers of -32 kDa subunits. The enzymes from these two classes are regulated by different mechanisms. Thioredoxin of mediated thiol-disulfide exchange interconverts eukaryotic PRKs between reduced (active) and oxidized (inactive) forms. Allosteric effectors, including activator NADH and inhibitors AMP and phosphoenolpyruvate, regulate activity of prokaryotic PRK. The effector binding site has been identified in the high resolution structure recently elucidated for prokaryotic PRK and the7 apparatus for transmission of the allosteric stimulus has been identified. Additional contrasts between PRKs include marked differences in primary structure between eukaryotic and prokaryotic PRKs. Alignment of all available deduced PRK sequences indicates that less than 10% of the amino acid residues are invariant. In contrast to these differences, the mechanism for ribulose 1,5-biphosphate synthesis from ATP and ribulose 5-phosphate (Ru5P) appears to be the same for all PRKs. Consensus sequences associated with M++-ATP binding, identified in all PRK proteins, are closely juxtaposed to the residue proposed to function as general base catalyst. Sequence homology and mutagenesis approaches have suggested several residues that may potentially function in Ru5P binding. Not all of these proposed Ru5P binding residues are closely juxtaposed in the structure of unliganded PRK. Mechanistic approaches have been employed to investigate the amino acids which influence K(m Ru5P) and identify those amino acids most directly involved in Ru5P binding. PRK is one member of a family of phospho or sulfo transferase proteins which exhibit a nucleotide monophosphate kinase fold. Structure/function correlations elucidated for PRK suggest analogous assignments for other members of this family of proteins.
Adv Enzymol Relat Areas Mol Biol 2000
PMID:Phosphoribulokinase: current perspectives on the structure/function basis for regulation and catalysis. 1080 May 94

We have examined adenosine (Ado) suppression of FSH-induced germinal vesicle breakdown (GVB) and its relationship to purine de novo synthesis. Oocyte-cumulus cell complexes (OCC) from PMSG-primed, immature mice were cultured 17-18 hr in medium containing 4 mM hypoxanthine (HX) or 300 microM dibutyryl cAMP (dbcAMP) to maintain meiotic arrest, and FSH was added to stimulate meiotic maturation. In the absence of FSH, Ado (1-250 microM) had no effect in dbcAMP-arrested oocytes but dose-dependently suppressed maturation in HX-treated oocytes. FSH-induced maturation was prevented by Ado, though more effectively in dbcAMP-supplemented cultures. Ado affected the magnitude, but not the kinetics pattern, of the response to FSH. Inosine also blocked meiotic induction, but only in dbcAMP-arrested oocytes. Purine de novo synthesis was nearly doubled in OCC by FSH treatment, and this response was completely prevented by Ado. FSH had no effect on HX salvage, although Ado reduced this activity by 98%. Inosine effects on metabolism were intermediate between the control and Ado groups. Experiments with radiolabeled energy substrates showed that Ado suppressed FSH activation of the pentose phosphate pathway but did not prevent significant activation of glycolysis or oxidation of pyruvate. Finally, in cultured follicles from primed mice, hCG-induced maturation was blocked by Ado as effectively as by the purine de novo synthesis inhibitor, azaserine. It is concluded that Ado has an inhibitory action on hormone-induced maturation that is due, at least in part, to suppression of glucose metabolism, leading to compromised purine de novo synthesis.
Mol Reprod Dev 2000 Jun
PMID:Adenosine blocks hormone-induced meiotic maturation by suppressing purine de novo synthesis. 1081 49

In response to overfeeding, the Landes goose develops a fatty liver that is twice as large as that of the Poland goose, despite similar food intake. The role of hepatic lipogenesis in the genetic susceptibility to fatty liver was assessed in male overfed geese of the two breeds. For a similar hepatic protein content, total activities of malic enzyme, glucose-6-phosphate dehydrogenase, acetyl-Coa-carboxylase and fatty acid synthase, and specific activity and mRNA level of malic enzyme were about two-fold higher in the Landes goose. In the Poland goose, the weight of the fatty liver was correlated positively with the specific activity of ME and the VLDL concentration, which was not the case in the Landes breed. These results show that: (1) hepatic lipogenesis remains very active until the end of the overfeeding period; (2) the pentose-phosphate pathway may function in birds, contrary to what is assumed usually; (3) the level of hepatic lipogenesis is a major factor in the susceptibility to hepatic steatosis in different breeds of geese; and (4) ME activity may be a limiting factor of lipid synthesis in the less susceptible Poland breed.
Comp Biochem Physiol B Biochem Mol Biol 2000 May
PMID:Role of hepatic lipogenesis in the susceptibility to fatty liver in the goose (Anser anser). 1082 67

The cbb(I) and cbb(II) operons encode structural genes which are important for carbon dioxide fixation via the Calvin-Benson-Bassham reductive pentose phosphate pathway in Rhodobacter capsulatus. Each operon is regulated by cognate LysR-type transcriptional activators, CbbR(I) and CbbR(II), with the product of the cbbR(I) gene, CbbR(I), able to control its own transcription under some growth conditions. Furthermore, CbbR(I) may at least partially regulate the cbb(II) operon, with significant, yet regulated transcription of the cbb(II) operon occurring in the absence of any CbbR. These results suggested the importance of additional regulators. Thus, in addition to the rather specific control exerted by CbbR, a more globally significant regulatory system, the RegA-RegB (PrrA-PrrB) two-component system, was found to contribute to transcriptional regulation of each cbb operon. The regA and regB mutant strains were found to contain constitutive levels of form I and form II RubisCO, the major proteins encoded by the cbb(I) and cbb(II) operons, respectively. In addition, DNaseI footprint analyses indicated that RegA*, a constitutively active mutant form of RegA, binds specifically to cbb(I) and cbb(II) promoter-operator regions. CbbR(I), CbbR(II), and RegA binding loci were localized relative to transcription start sites, leading to a coherent picture of how each of these regulators interacts with specific promoter-operator sequences of the cbb operons.
J Mol Biol 2000 Jul 28
PMID:Multiple regulators and their interactions in vivo and in vitro with the cbb regulons of Rhodobacter capsulatus. 1090 56

Unlike its predecessors B. subtilis rosR and 41, riboflavin producing B. subtilis 24 strain does not utilize pentose and gluconate and poorly assimilates glucose. Simultaneous addition of glutamic and shikimic acid restored its capacity to grow and produce riboflavin in medium with pentose and gluconate. This strain lacks the activity of transketolase, the key enzyme of the pentose phosphate cycle, and possesses normal ribulose-5-phosphate-epimerase and glucose phosphate isomerase activities. Like enterobacteria, B. subtilis has two different transport systems for glucose and mannose. The data are discussed from the viewpoint of increasing riboflavin production by transketolase mutants. Probable consequences of cell wall and cytoplasmatic membrane damage in B. subtilis with this mutation are discussed.
Mol Gen Mikrobiol Virusol 2000
PMID:[Transketolase mutation in riboflavin-synthesizing strains of Bacillus subtilis]. 1097 72


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