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PubMedDate not supplied

The control of trehalose biosynthesis in Saccharomyces cerevisiae: evidence for a catabolite inactivation and repression of trehalose-6-phosphate synthase and trehalose-6-phosphate phosphatase.

During diauxic growth of yeast in glucose-rich medium, the accumulation of trehalose started well after complete exhaustion of glucose from the medium. The accumulation of the disaccharide was concomitant with a resumption of cell growth on the ethanol accumulated in the medium, but not with a degradation of glycogen which occurred as soon as glucose had been consumed. In contrast, in a mutant deficient in phosphoenolpyruvate carboxykinase, the synthesis of trehalose coincided exactly with the degradation of glycogen. Upon inoculation of stationary phase wild-type cells into a glucose medium, the activities of trehalose-6-phosphate (Tre6P) synthase and Tre6P phosphatase dropped in parallel to reach only 15% of their initial values after 3 h, and only recovered their original values as cells re-entered stationary phase. In the presence of cycloheximide, the decrease in Tre6P synthase and Tre6P phosphatase activities was restricted to 50-60%, the remaining decrease being inhibited by the drug. Furthermore, the reappearance of the enzyme activities following transfer of cells to an acetate medium was blocked by cycloheximide. It was also shown that loss of activity of these two enzymes required a combination of metabolizable sugars together with a nitrogen source. Low activities of Tre6P synthase and Tre6P phosphatase were measured in mutants with increased adenylate cyclase activity (RAS2ala18val19 mutants). Moreover, derepression of these enzymes at the approach of stationary phase was prevented in a pde2 mutant when it was cultivated in the presence of exogenous cyclic nucleotide. The mechanism of this effect is not clear, but may involve a transcriptional regulation by cAMP of the genes encoding these proteins.

Culture Media↗
PubMed1992

Mutations in phosphofructokinases alter the control characteristics of glycolysis in vivo in Saccharomyces cerevisiae.

Ethanol and CO2 production from glucose by non-proliferating suspensions of aerobically-grown, glucose-derepressed wild-type Saccharomyces cerevisiae is inhibited by O2; monitoring by mass spectrometry provides a direct method for measurement of the Pasteur effect. Under aerobic conditions, that part of the CO2 evolved equivalent to the O2 consumed, is produced by respiration: subtraction of this respiratory CO2 from the total gives CO2 produced by aerobic glycolysis. Pasteur quotients (anaerobic CO2/aerobic glycolytic CO2) were within the range 1.2 to 3.0. The Pasteur effect was not observed in the presence of carbonyl cyanide m-chlorophenylhydrazone, an uncoupler of mitochondrial energy metabolism, or in a rho degree cytoplasmic petite mutant. A 'non-allosteric' mutant with an altered regulatory subunit of phosphofructokinase showed no Pasteur effect. Strains bearing a nonsense mutation pfk1 in the catalytic subunit of soluble phosphofructokinase (PFKI) also showed no Pasteur effect; the residual fermentative activity of this strain was dependent on PFKII, the particulate phosphofructokinase. A double mutant lacking both PFKI and glucose-6-phosphate dehydrogenase showed similar characteristics to those of the single pfk1 mutant; this indicates that the hexose monophosphate shunt is not acting to bypass the phosphofructokinase block. A 'hyper-allosteric' mutant altered in the regulatory subunit encoded by the gene PFK2 showed characteristics of glucose fermentation and ethanol oxidation very similar to those of wild-type organisms. These results indicate that either of the two phosphofructokinases can carry out glycolysis.

Aerobiosis↗
PubMed1995

Functional organization of mammalian hexokinases: characterization of chimeric hexokinases constructed from the N- and C-terminal domains of the rat type I and type II isozymes.

Chimeric hexokinases consisting of either the N-terminal half of Type I hexokinase fused with the C-terminal half of the Type II isozyme (NICII) or the inverse pair (NIICI), along with the parental isozymes, were expressed in COS-1 cells. The thermal stability of the chimeras was intermediate between that of the highly labile Type II isozyme and the relatively stable Type I hexokinase. In their Kms for substrates, Glc and ATP, the chimeric enzymes were similar to the parental isozyme from which the C-terminal half was derived. Although the Type I and Type II isozymes were similar in their sensitivity to inhibition (competitive vs ATP) by the Glc-6-P analogs, 1,5-anhydroglucitol 6-phosphate (AnGlc-6-P), and Glc-1,6-bisphosphate, the chimeric enzymes differed markedly, with the NIICI chimera being much more sensitive and the NICII chimera much less sensitive than either parental form to these inhibitors. In contrast, the response of the chimeras to Pi, either as an antagonist of inhibition by AnGlc-6-P or, at higher concentrations, as an inhibitor, was correlated with the origin of the N-terminal domain. The results are consistent with the view that catalytic function is associated with the C-terminal domain of the Type I isozyme, with regulatory function--inhibition by Glc-6-P and its analogs and antagonism of this inhibition by Pi--being mediated by the N-terminal domain.

Adenosine Triphosphate↗
PubMed1995

Metabolism of fructose-3-phosphate in the diabetic rat lens.

Fructose-3-phosphate and sorbitol-3-phosphate are produced in diabetic rat lenses by a 3-phosphokinase. While sorbitol-3-phosphate appears to be an inert polyol phosphate, fructose-3-phosphate is a potent cross-linking agent and a potential in vivo source of 3-deoxyglucosone. The objective of this study was to investigate the production and decomposition of fructose-3-phosphate in the diabetic rat lens. The results indicate that this metabolite achieves a steady-state concentration of almost 1 mumol/g wet weight within 2 weeks after the onset of diabetes. These steady-state levels appear to be a consequence of a balance between its production from fructose and its further decomposition to 3-deoxyglucosone. This conclusion is supported by results from disappearance of fructose-3-phosphate in insulin-treated diabetic rats and in vitro incubations of fructose-3-phosphate with amines where production of 3-deoxyglucosone was detected using a number of different methods including mass spectrometry. In agreement with these results, elevated concentrations of 3-deoxyglucosone along with its detoxification product, 3-deoxyfructose, were detected in the diabetic rat lenses. Other sugars and sugar phosphates which were detectable in the diabetic rat lenses were glucose, fructose, glucose-6-phosphate, fructose-6-phosphate, and sedoheptulose-7-phosphate. In conclusion, results from this study suggest that fructose-3-phosphate and 3-deoxyglucosone are likely to be important contributors to the process of nonenzymatic glycation in diabetic rat lenses.

Animals↗
PubMed1996

A comparison of the renal and hepatic microsomal glucose-6-phosphatase enzymes.

The liver glucose-6-phosphatase enzyme has been extensively characterized and relatively little is known about the renal microsomal glucose-6-phosphatase enzyme. The reason for lack of study of the renal glucose-6-phosphatase enzyme is that it has been assumed to be the same as the liver enzyme. Immunoblotting with antibodies raised against the liver enzyme revealed differences in apparent molecular weight and antigenicity between the liver and kidney glucose-6-phosphatase enzyme proteins. Characterization of the activity of the renal glucose-6-phosphatase enzyme also showed that it is regulated differently to the liver enzyme in some metabolic states. This implies that the renal and liver glucose-6-phosphatase enzymes may have different roles.

Animals↗
PubMed2000

Membrane potential-dependent conformational changes in mitochondrially bound hexokinase of brain.

Previously characterized monoclonal antibodies (Mabs) were used in a study of Type I hexokinase from rat brain. Based on the relative reactivity of these Mabs with soluble and mitochondrially bound forms, binding to mitochondria was shown to affect specific epitopic regions in both N- and C-terminal halves of the enzyme and to modulate conformational changes induced by binding of the ligands, Glc or ATP. Reactivities with Mabs recognizing epitopes in two defined regions of the N-terminal half and one defined region of the C-terminal half of the mitochondrially bound enzyme were selectively affected by mitochondrial membrane potential, or by addition of oligomycin, carboxyatractyloside, or bongkrekic acid. The Glc-6-P analog, 1 ,5-anhydroglucitol-6-P, was much more effective as a competitive inhibitor against extramitochondrial ATP than against intramitochondrial ATP generated by oxidative phosphorylation. These results provide further insight into the role of hexokinase-mitochondrial interactions in regulation of cerebral glucose metabolism.

Adenosine Triphosphate↗
PubMed2002

Kinetic and regulatory properties of HK I(+), a modified form of the type I isozyme of mammalian hexokinase in which interactions between the N- and C-terminal halves have been disrupted.

A modified form (HK I(+)) of rat Type I hexokinase (HK I) has been expressed. HK I(+) contains a centrally located polyalanine insert which, along with the known helical propensity of adjacent sequence, was expected to lead to alpha-helix formation, with resulting distension of the molecule and disruption of interactions between the N- and C-terminal halves. The properties of HK I(+) are consistent with this expectation and with previous proposals that (1) inhibition of HK I by Glc-6-P or its analogs and antagonism of this inhibition by P(i) result from competition of these ligands for a binding site in the N-terminal half of HK I, with resulting conformational changes propagated through interactions with the catalytic C-terminal half, and (2) binding of Glc-6-P to a site in the C-terminal half of HK I is obstructed by interactions between the halves, present in HK I but not HK I(+).

Amino Acid Sequence↗
PubMed1994

Use of capillary affinity electrophoresis for the determination of lectin-sugar interactions.

Capillary affinity electrophoresis was used to study the interactions of lectins from Tetragonolobus purpuras with L-(-)-fucose 1-phosphate. The electrophoretic mobilities of three lectin peaks were influenced by the complexation with the negatively charged fucose derivative. A model that allows the calculation of the complex formation constant from the change in mobility at different concentrations of fucose 1-phosphate has been derived. Calcium ions added to the buffer solution promoted the complex formation of the three lectins. This technique required only minute amounts of the lectins and enabled the simultaneous study of the complex formation of several proteins.

Calcium↗
PubMed1998

Cleanup and analysis of sugar phosphates in biological extracts by using solid-phase extraction and anion-exchange chromatography with pulsed amperometric detection.

A cleanup method based on anion-exchange solid-phase extraction (SPE) was developed to render biological extracts suitable for the analysis of hexose phosphates with a modified anion-exchange chromatography method and pulsed amperometric detection. The method was applied to cell extracts of Saccharomyces cerevisiae obtained by using cold methanol as quenching agent and chloroform as extraction solvent. It was shown that pretreatment of the cell extract with SPE markedly improved the quality of the liquid chromatography analysis with recoveries of the sugar phosphates close to 100%. Furthermore, the method allowed for sample enrichment and the original extraction procedure could be simplified by implementing SPE early in the extraction protocol.

Cell Fractionation↗
PubMed2000

Structures of l-fuculose-1-phosphate aldolase mutants outlining motions during catalysis.

The crystal structures of l-fuculose-1-phosphate aldolase (FucA) with and without a ligated analogue of dihydroxyacetone phosphate (DHAP) and of a number of active center mutants have resulted in a model of the catalytic mechanism. This model has now been confirmed by structural analyses of further mutations at the zinc coordination sphere and at the phosphate site. In addition, these mutants have revealed new aspects of the catalysis: the hydroxyl group of Tyr113' (from a neighboring subunit), which sits just outside the zinc coordination sphere, steers DHAP towards a productive binding mode at the zinc ion; Glu73 contacts zinc in between the two ligand positions intended for the DHAP oxygen atoms and thus avoids blocking of these positions by a tetrahedrally coordinated hydroxy ion; the FucA polypeptide does not assume its minimum energy state but oscillates between two states of elevated energy as demonstrated by a mutant in a minimum energy state. The back and forth motion involves a mobile loop connecting the phosphate site with intersubunit motions and thus with the Brownian motion of the solvent. The phosphate group is bound strongly at a given distance to the zinc ion, which prevents the formation of too tight a DHAP:zinc complex. This observation explains our failure to find mutants that accept phosphate-free substitutes for DHAP. The FucA zinc coordination sphere is compared with that of carbonic anhydrase.

Aldehyde-Lyases↗
PubMed1986

The effect of short chain fatty acid administration on hepatic glucose, phosphate, magnesium and calcium metabolism.

Intra peritoneal administration of the short chain fatty acids, acetate, propionate and butyrate, in amounts calculated to reach 20 mM in total body water were given to fed and 48 hour starved male Wistar rats. One half hour after administration, the livers were freeze-clamped and the hepatic contents of various intermediary metabolites were measured. The liver content of total glycolytic intermediates was elevated by short chain fatty acids. In fed animals, the portion of glycolysis from fructose 1,6-bisphosphate (FBP) to PEP was elevated 2 to 4 fold. In 48 hour starved animals, where gluconeogenesis is active, the portion of the gluconeogenetic pathway from FBP to glucose was elevated 1.5 to 3.5 fold with the exception of the butyrate treated animals where blood glucose was not elevated. The metabolites of the hexose-monophosphate pathway that were measured, namely 6-phosphogluconate, ribulose 5-phosphate and xylose 5-phosphate were increased in both fed and starved animals. The free cytoplasmic [NAD+]/[NADH], [NADP+]/[NADPH], and [epsilon ATP]/[epsilon ADP] X [epsilon Pi] ratios were all decreased in both fed and starved animals after short chain fatty acid administration. The liver content of calcium increased 1.2 to 2 fold in fed animals and 2 to 3 fold in starved animals while total liver magnesium was either unchanged or increased only 1.2 times. The liver pyrophosphate (PPi) content increased a minimum of 10 fold in fed animals and over 100 fold in starved animals. In all cases no PPi could be detected in vivo by 31P NMR even though in the starved rats the PPi levels approached those of ATP. The liver content of inorganic Pi increased 1.3 to 1.5 fold in fed animals and 1.5 to 2 fold in starved animals. The total "rapidly metabolizing" Pi pool, that includes adenine and guanine nucleotides, glycolytic and shunt intermediates, Pi and PPi increased 1.3 times in fed animals (from 13.8 mumole/g fresh weight) and 1.5 to 1.7 fold in starved animals (from 15.7 mumol/g fresh weight). The total phosphate taken up from blood and entering the rapidly turning over pool of liver phosphate ranged between 4 and 12 mumols/g of liver.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenine Nucleotides↗
PubMed1982

Stimulation of the hexose monophosphate shunt activity in human polymorphonuclear leukocytes.

The glucose metabolism in human polymorphonuclear (PMN) leukocytes was stimulated by latex particles, zymosan particles, gamma-G globulin and formylmet-leu-phe (FMLP) peptide. Maximum stimulation occurred when zymosan particles in amounts above 0.25 mg/ml per 4 X 10(6) leukocytes were used. Latex particles, gamma-G globulin and FMLP stimulated the glucose oxydation less than zymosan particles. The glucose oxydation increase in proportion to the amount of latex particles and gamma-G globulin in the measured range, while the dose response curve using FMLP shows maximum activity at a consentration of the peptide of 5 X 10(-5)M per 4 X 10(6) leukocytes. It is likely that FMLP and gamma-G globulin act on the glucose metabolism via cell surface receptors. The synthetic polystyrene particles (latex) do not occupy these receptors, but stimulate the hexose monophosphate (HMP) shunt activity of the PMN via intracellular mechanisms. Opsonized zymosan particles seem to act on the leukocyte glucose metabolism via cell surface receptors as well as via intracellular mechanisms.

Glucose↗