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PubMed1997

Phenotypic analysis of ovarian carcinoma: polypeptide expression in benign, borderline and malignant tumors.

Studies of multiple markers in tumors are required for adequate biological characterization. We have characterized the expression of multiple proteins in human ovarian tumors using the technique of 2-dimensional gel electrophoresis (2-DE/PDQUEST). Tumor cells were prepared from the tissue of 22 ovarian tumors. Large variations were observed between tumors in the expression of various polypeptides, indicating heterogeneity in gene expression. An increase in the spot density of 2 cell-cycle-related proteins, PCNA and OP18/stathmin, was observed in carcinomas. Borderline tumors expressed low levels of these proteins. Significant increases in the levels of nm23, GST-pi, elongation factor 2 and triose phosphate isomerase were recorded in ovarian carcinomas. Furthermore, decreases in the levels of tropomyosin-2 and lamin C were observed in malignant as compared with benign tumors. The pattern of expression of 9 protein markers was examined in individual tumors. All malignant tumors showed simultaneous alterations in the expression of 5 or more of these proteins, whereas no benign tumor showed alterations in the expression of more than 3 polypeptides. Borderline tumors showed alterations in 0 to 6 markers. We conclude that the simultaneous analysis of multiple polypeptides, which can be achieved by 2-DE, is useful for characterization of gene expression and diagnostic studies in ovarian tumors.

Adult↗
PubMed1998

Occurrence of the Crabtree effect in HeLa cells.

The occurrence of a Crabtree effect in HeLa cells was detected. Some properties of pyruvate kinase (PK) were also evaluated. Hexose phosphate, triose-phosphate and phosphoenolpyruvate (PEP) significantly decreased the oxygen consumption of digitonin-permeabilized HeLa cells, which were oxidizing succinate. The Crabtree effect promoted by PEP was concentration-dependent and was lowered by an increase of ADP concentration, suggesting a participation of PK. The dependence of fructose-1,6-bisphosphate (FDP) by HeLa cell PK was observed. The PK of HeLa cells was inhibited by L-alanine only in the absence of FDP, while in the presence of the metabolite, an increase in the activity was observed. PK was also inhibited in the presence of L-histidine and L-leucine, while L-serine promoted activation. L-Cysteine and L-phenylalanine also inhibited the PK of HeLa cells. This, together with the sigmoidal character in relation to substrate concentration, suggests the presence of the K-type of PK in HeLa cells.

Cell Division↗
PubMed2000

Release characteristics of a short-chain fatty acid, n-butyric acid, from its beta-cyclodextrin ester conjugate in rat biological media.

6(A)-O-(n-Butanoyl)-beta-cyclodextrin was prepared and its hydrolysis behavior in aqueous solutions and in rat intestinal fluids was investigated. Furthermore, the enzymatic hydrolyses of the n-butyric acid-beta-cyclodextrin conjugate using alpha-amylase and esterase were studied to gain insight into the release behavior of n-butyric acid from the conjugate. The hydrolysis of the conjugate proceeded according to a first-order kinetics in aqueous solution, and gave a V-shaped pH profile, indicating a specific acid-base-catalyzed hydrolysis at acidic and neutral-alkaline regions, respectively. The half-lives (t(1/2)) of the conjugate at pH 4.4, 6.8, and 7.4 at 37 degrees C were approximately 580, 43, and 6 days, respectively, indicating that the conjugate is stable in aqueous solution. No appreciable release of n-butyric acid from the conjugate was observed in the stomach and small intestinal contents of rats, or in the small and large intestinal homogenates of rats. On the other hand, a fast disappearance of the conjugate and an appearance of n-butyric acid were observed in the cecal and colonic contents of rats. The t(1/2) values of the disappearance were approximately 4, 1, and 6 h in 10 and 15% cecal contents and 10% colonic contents, respectively, and the appearance of n-butyric acid after 6 h was approximately 10% in the 15% cecal contents. Aspergillus oryzae alpha-amylase hydrolyzed the conjugate to small saccharide conjugates, such as the triose and maltose conjugates, but there was no appreciable release of n-butyric acid. The conjugate was less susceptible to carboxylic esterase (from porcine live), thus releasing no appreciable amounts of n-butyric acid. On the other hand, a fast release of n-butyric acid was observed when the esterase was employed after amylase hydrolysis, suggesting that two types of enzymes, sugar-degrading and ester-hydrolyzing enzymes, are necessary for the release of n-butyric acid from the conjugate in large intestinal contents.

Animals↗
PubMed2001

Analysis of the serologic response to systemic Candida albicans infection in a murine model.

Two different strains of mice with different susceptibilities to systemic candidiasis (BALB/c and CBA/H) were infected with Candida albicans SC5314. Immune sera were obtained on different days post-infection and assayed against two-dimensional polyacrylamide gel electrophoresis separation of cytoplasmic extracts obtained from protoplasts. More than 31 immunoreactive proteins were detected. Some of them were identified and found to correspond to (i) glycolytic enzymes, such as fructose biphosphate aldolase, triose phosphate isomerase (TPIS), glyceraldehyde-3-phosphate dehydrogenase, 3-phosphoglycerate kinase (PGK), enolase (ENO1) and pyruvate kinase, (ii) other metabolic enzymes, such as methionine synthase (METE), inosine-5'-monophosphate dehydrogenase (IMH3), alcohol dehydrogenase and aconitate hydratase and (iii) heat shock proteins: HS71 (or Ssa1p) and HS75 (or Ssb1p), both from the HSP70 family. This work reports for the first time antigenic properties for IMH3 and TPIS. Different profiles of antibody expression, depending on the mouse strain and the course of infection, were observed. ENO1 was the most immunogenic protein in infected BALB/c mice (the most resistant strain). On the other hand, sera from CBA/H mice (a more susceptible strain) showed a strong increase in reactivity along the infection against METE, HS75 and PGK. Many of these immunoreactive proteins have also been detected using sera from human patients with systemic candidiasis, thus indicating the usefulness of the murine model for studying the antibody response in systemic candidiasis. In this work we demonstrate that the combination of two-dimensional electrophoresis with immunoblotting using murine immune sera can be an important tool for the identification of C. albicans antigens and for monitoring the evolution of the disease.

Amino Acid Sequence↗
PubMed1978

The living state and cancer.

The surrounding world can be divided into two parts: alive and inanimate. What makes the difference is the subtle reactivity of living systems. The difference is so great that it is reasonable to suppose that what underlies life is a specific physical state, 'the living state'. Living systems are built mainly of nucleic acids and proteins. The former are the guardians of the basic blueprint while the business of life is carried on by proteins. Proteins thus have to share the subtle reactivity of living systems. A closed-shell protein molecule, however, has no electronic mobility, and has but a low chemical reactivity. Its orbitals are occupied by electron pairs which are held firmly. The situation can be changed by taking single electrons out of the system. This unpairs electrons, leaves half-occupied orbitals with positive electron holes, making the molecules into highly reactive paramagnetic free radicals. The reactivity of the system depends on the degree of its electronic desaturation. Electrons can be taken out of protein molecules by 'electron aceptors' in 'cahrge transfer'. When life began, our globe was covered by dense water vapour. There was no light and no free oxygen. Electron acceptors could be made out of trioses by concentrating their carbon atoms as carbonyls at one end of the molecule. The resulting methylglyoxal is a weak acceptor which made a low level of development possible. When light appeared, free oxygen was generated by the energy of photons. Oxygen is a strong electron acceptor. Its appearance opened the way to the present level of development. The transfer of electrons from protein to oxygen is effected by a complex chemical mechanism which involves ascorbic acid.

Animals↗
PubMed1983

The role of mobility in the substrate binding and catalytic machinery of enzymes.

Recent theoretical and experimental studies have demonstrated that proteins are fluctuating systems capable of large, seemingly random, excursions from the equilibrium conformation. Attention is now focusing on the functional consequences of these motions. X-ray diffraction is a powerful tool for mapping the spatial distribution of protein dynamics; studies on the temperature dependence of the apparent Debye-Waller factors of crystalline myoglobin demonstrate that proteins are flexible in the solid state. Crystallographic studies of a Michaelis complex of ribonuclease A show that a mobile lysine adapts its conformation to the changes in stereochemistry and charge distribution in the substrate during catalysis. The structure of the triose phosphate isomerase-substrate complex shows that a mobile region of 10 amino acids becomes ordered when ligand binds. These studies suggest several roles for protein mobility in enzymic catalysis: providing access to internal sites, allowing changes in substrate structure during the reaction, and reducing the observed binding constant of substrate and product to the enzyme by decreasing entropy. A flexible enzyme also does not need a communication system to signal binding or transformation, since a pre-existing equilibrium can be used. More speculative ideas, such as the guiding of thermal vibrations along the reaction coordinate, can only be tested when more detailed data are available.

Binding Sites↗
PubMed1985

Enzyme activities of cultured erythroblasts.

The enzyme activities of cultured early erythroid progenitor cells (burst-forming unit erythroid, BFU-E) were measured and were compared with the activities of mature erythrocytes. The enzyme activity of acetylcholinesterase was not detectable in the erythroblasts. The ratios of phosphofructokinase and glutathione peroxidase were low due to low enzyme activities in both the erythroblasts and erythrocytes. The ratios of triose phosphate isomerase, phosphoglycerate kinase, and adenylate kinase were low due to high enzyme activities in both the erythroblasts and erythrocytes. The ratios of hexokinase, glucose phosphate isomerase, monophosphoglyceromutase, pyruvate kinase, and adenosine deaminase were high due to high enzyme activities in the erythroblasts. The isozyme of erythroblast hexokinase was of the prototype isozyme I, while pyruvate kinase was predominantly of the prototype M2, with two hybrid isozymes to the anodal side by electrophoresis. These facts suggest that there is a greatly different metabolic pattern during the maturation of the erythroid cells.

Cells, Cultured↗
PubMed2002

Seasonal changes in glycerol content and enzyme activities in overwintering larvae of the Shonai ecotype of the rice stem borer, Chilo suppressalis Walker.

Enzymes associated with glycogen metabolism and glycerol synthesis in larvae of the Shonai ecotype of the rice stem borer, Chilo suppressalis, were investigated over the winter in 2000-2001. Glycerol content was scarcely detected in September and October, rapidly increased in November and December, peaked in January, and then decreased. Glycogen was converted to glycerol over the winter until February, and glycerol was reconverted to glycogen in March. The trehalose content remained constant over the winter. The activities of enzymes associated with glycerol synthesis changed with the season. Glycerol accumulation was accomplished by activation of glycogen phosphorylase, inhibition of fructose-1,6-bisphosphatase and pyruvate kinase, and activation of enzymes associated with glycerol synthesis, mainly glyceraldehyde-3-phosphatase and polyol dehydrogenase with glyceraldehyde activity. These changes led to a diversion of triose phosphates into the pathway of glycerol synthesis. However, activities of the two initial enzymes of the hexose monophosphate shunt were not activated and remained relatively constant, but high during the period of active glycerol synthesis. Both decreasing temperature in the field and the transition from the diapause to the post-diapause state may be responsible for the changes in activities of enzymes associated with glycerol synthesis.

Animals↗
PubMed2007

Fluorogenic substrates for lipases, esterases, and acylases using a TIM-mechanism for signal release.

3-Acyloxyl-2-oxopropyl ethers of umbelliferone were investigated as new fluorogenic substrates for lipases and esterases. The aliphatic primary alcohol-leaving group released the fluorescent product umbelliferone by an enolization/beta-elimination reaction similar to the triose phosphate isomerase (TIM) reaction. A similarly designed phenylacetamide provided a fluorescent probe for penicillin G acylase, whereby the enolization/beta-elimination sequence from the intermediate aminoketone was very fast and spontaneous even under acidic conditions. The corresponding epoxyketone was not fluorogenic with epoxide hydrolases (EH). These substrates represent periodate-free Clips-otrade mark substrates.

Acetamides↗
PubMed2002

The association between a negatively charged ligand and the electronegative binding pocket of its receptor.

Many examples exist of charged amino acids that play a role in attracting or holding a charged ligand toward or inside an oppositely charged binding pocket of the protein. For example, the enzymes superoxide dismutase, triose-phosphate isomerase, and acetylcholinesterase can steer ligands toward their oppositely charged binding pockets or gorges. Interestingly, in our Brownian dynamics simulations of a phosphate-binding protein, we discovered that negatively charged phosphate (HPO(2-)(4)) could make its way into the negatively charged binding pocket. In fact, the phosphate-binding protein exhibits counterintuitive kinetics of association. That is, one would expect that the rate of association would increase on increases to the ionic strength since the interaction between the ligand, with a charge of -2, and the electronegative binding pocket would be repulsive and greater screening should reduce this repulsion and increase the rate of association. However, the opposite is seen-i.e., the rate of association decreases on increases in the ionic strength. We used Brownian dynamics techniques to compute the diffusion limited association rate constants between the negatively charged phosphate ligand and several open forms of PBP (wild-type and several mutants based on an x-ray structure of open-form PBP, mutant T141D). With the appropriate choices of reaction criteria and molecular parameters, the ligand was able to diffuse into the binding pocket. A number of residues influence binding of the ligand within the pocket via hydrogen bonds or salt bridges. Arg135 partially neutralizes the charges on the HPO(2-)(4) ligand in the binding pocket, allowing it to enter. It is also found that the positive electrostatic patches above and below the binding entrance of PBP contribute the major attractive forces that direct the ligand toward the surface of the protein near the binding site.

Bacterial Proteins↗
PubMed1985

The interaction between gluconeogenic metabolism and accumulation of phosphate by chick kidney tubule cells.

Pyruvate promotes both phosphate uptake and glucose synthesis by isolated chick kidney proximal tubule cells. 3-Mercaptopicolinate inhibits both glucose synthesis and the promoted phosphate accumulation to the same extent. Glycerol also stimulates glucose synthesis, but does not affect phosphate accumulation. Oxygen utilization by the tissue is slightly stimulated by glycerol and pyruvate, but the enhancement of uptake by pyruvate is unlikely to result from raised cellular oxidative phosphorylation. The action of pyruvate is not a direct effect on the phosphate transporter, or on the transport of phosphate across the basolateral membrane, but entails an obligatory flux to triose phosphate.

Animals↗
PubMed1989

Inhibition of the glycolytic pathway by methylglyoxal in human platelets.

The incubation of human platelets with methylglyoxal and glucose produces a rapid transformation of the ketoaldehyde to D-lactate by the glyoxalase system and a partial reduction in GSH. Glucose utilization is affected at the level of the glycolytic pathway. No effect of the ketoaldehyde on glycogenolysis and glucose oxidation through the hexose monophosphate shunt was demonstrated. Phosphofructokinase, fructose 1,6 diphosphate (F1, 6DP) aldolase, glyceraldehyde 3-phosphate dehydrogenase and 3-phosphoglycerate mutase were mostly inhibited by methylglyoxal. A decrease in lactate and pyruvate formation and an accumulation of some glycolytic intermediates (fructose 1,6 diphosphate, dihydroxyacetone phosphate, 3-phosphoglycerate) was observed. Moreover methylglyoxal induced a fall in the metabolic ATP concentration. Since methylglyoxal is an intermediate of the glycolytic bypass system from dihydroxyacetone phosphate to D-lactate, it may be assumed that ketoaldehyde exerts a regulating effect on triose metabolism.

Adenine Nucleotides↗
PubMed2005

Mechanism and substrate specificity of tRNA-guanine transglycosylases (TGTs): tRNA-modifying enzymes from the three different kingdoms of life share a common catalytic mechanism.

Transfer RNA-guanine transglycosylases (TGTs) are evolutionarily ancient enzymes, present in all kingdoms of life, catalyzing guanine exchange within their cognate tRNAs by modified 7-deazaguanine bases. Although distinct bases are incorporated into tRNA at different positions in a kingdom-specific manner, the catalytic subunits of TGTs are structurally well conserved. This review provides insight into the sequential steps along the reaction pathway, substrate specificity, and conformational adaptions of the binding pockets by comparison of TGT crystal structures in complex with RNA substrates of a eubacterial and an archaebacterial species. Substrate-binding modes indicate an evolutionarily conserved base-exchange mechanism with a conserved aspartate serving as a nucleophile through covalent binding to C1' of the guanosine ribose moiety in an intermediate state. A second conserved aspartate seems to control the spatial rearrangement of the ribose ring along the reaction pathway and supposedly operates as a general acid/base. Water molecules inside the binding pocket accommodating interaction sites subsequently occupied by polar atoms of substrates help to elucidate substrate-recognition and substrate-specificity features. This emphasizes the role of water molecules as general probes to map binding-site properties for structure-based drug design. Additionally, substrate-bound crystal structures allow the extraction of valuable information about the classification of the TGT superfamily into a subdivision of presumably homologous superfamilies adopting the triose-phosphate isomerase type barrel fold with a standard phosphate-binding motif.

Archaea↗
PubMed1991

Pentosidine: a molecular marker for the cumulative damage to proteins in diabetes, aging, and uremia.

Collagen undergoes progressive browning with age and diabetes characterized by yellowing, fluorescence, and cross-linking. The present research was undertaken in order to investigate the nature of the collagen-linked fluorescence. Human collagen was exhaustively cleaved into peptides by enzymatic digestion. Upon purification, a highly fluorescent chromophore was identified and purified from old human collagen. Structure elucidation revealed the presence of an imidazo [4,5-b] pyridinium-type structure acting as a cross-link between arginine, lysine, and a pentose. This advanced glycosylation end-product and protein cross-link results from the reaction of pentoses with proteins and was named pentosidine. Further work indicated that long-term glycosylation of proteins with hexoses also leads to pentosidine formation through sugar fragmentation. The proposed mechanism of pentosidine formation involves the dehydration of the pentose-derived Amadori compound to form an intermediate which is attacked under base catalysis by the guanido group of arginine. The strict requirement for the Amadori rearrangement is uncertain. However, oxidation is definitely involved since pentosidine is not formed in the absence of oxygen. Five-carbon sugars contributing to pentosidine formation could be formed from larger sugars by oxidative fragmentation or from trioses, tetroses, and ketoses by condensation and/or reverse aldol reactions. Pentosidine increases exponentially in human skin at autopsy. Mean age-adjusted skin levels were significantly increased in subjects with uremia and especially in type 1 diabetics with uremia vs. controls. In skin biopsy, levels were significantly elevated in all diabetic (type 1) vs. control subjects. The highest degree of association was with the cumulative grade of diabetic complication (retinopathy, nephropathy, arterial stiffness, and joint stiffness). Pentosidine also forms in various proteins other than collagen, although to a much lesser extent. In blood, pentosidine is mainly associated with plasma proteins and is highly elevated during uremia. In the lens, it is associated with both water-soluble and -insoluble protein fractions and is especially elevated during brunescent cataract formation. The origin of pentosidine in vivo is uncertain. Evidence suggests that the pentoses are the most reactive sugars in pentosidine formation in vitro; however, the origin and importance of free pentoses in vivo, especially during the diabetic state, are not certain. Possible origins include hemolysis and/or a defect in the primary pentose metabolism.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMedDate not supplied

Fructose-mediated non-enzymatic glycation: sweet coupling or bad modification.

The Maillard reaction is a process in which reducing sugars react spontaneously with amino groups in proteins to advanced glycation end products (AGEs). Although an elevated level of glucose had been thought to play a primary role in the Maillard reaction, on a molecular basis, glucose is among the least reactive sugars within biological systems. The formation of AGEs is now also known to result from the action of various metabolites other than glucose, which are primarily located intracellularly and participate in the non-enzymatic glycation reaction at a much faster rate, such as fructose, trioses and dicarbonyl compounds. In this review, we considered the glycation reaction with particular attention to the potential role of fructose and fructose metabolites. The two sources for fructose are an exogenous supply from the diet and the endogenous formation from glucose through the aldose reductase pathway. Despite its approximately eightfold higher reactivity, the contribution of extracellular glycation by fructose is considerably less than that by glucose, because of the low plasma concentration of fructose (5 mmol/L glucose vs 35 micro mol/L fructose). Intracellularly, fructose is elevated in a number of tissues of diabetic patients in which the polyol pathway is active. In the cells of these tissues, the concentrations of fructose and glucose are of the same magnitude. Although direct evidence is not yet available, it is likely that the high reactivity of fructose and its metabolites may substantially contribute to the formation of intracellular AGEs and may contribute to alterations of cellular proteins, dysfunction of cells and, subsequently, to vascular complications.

Animals↗
PubMed1988

Activators of protein kinase C depolarize insulin-secreting cells by closing K+ channels.

Carbohydrate stimuli of insulin secretion depolarize the pancreatic B cell and the B-cell line RINm5F by inhibiting ATP-sensitive K+ channels. We examined the possibility that this effect is mediated by activation of protein kinase C. In RINm5F cells, the triose D-glyceraldehyde evoked a rapid increase of the mass of 1,2-diacylglycerol, the endogenous activator of protein kinase C. This effect is mainly due to de novo synthesis of the lipid from glycolytic intermediates, as glyceraldehyde carbon was incorporated into 1,2-diacylglycerol within 1 min of exposure to 14C-labelled glyceraldehyde. The effects of two exogenous activators of kinase C, 4-beta-12-phorbol-myristate 13-acetate (PMA) and 1,2-didecanoylglycerol (DC10) on single K+ channel currents were examined in RINm5F cell-attached membrane patches. Both PMA and DC10 depolarized the cells and decreased the open-state probability of the ATP-sensitive K+ channels. These actions were not due to changes in cellular ATP content, since PMA, like glyceraldehyde, failed to alter cellular ATP. As is the case for glyceraldehyde, PMA and DC10 raised cytosolic free Ca2+ [( Ca2+]i) and stimulated insulin secretion. Both of these effects are inhibited in the absence of external Ca2+. This, and the attenuation of the [Ca2+]i rise by verapamil, suggest that all three stimuli raise [Ca2+]i by promoting Ca2+ influx through voltage-gated channels in turn leading to insulin secretion. As the exogenous activators of protein kinase C mimic the effects of glyceraldehyde, it is proposed that the carbohydrate-mediated production of 1,2-diacylglycerol constitutes the link between metabolism and membrane depolarization.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1995

Crystal structure of the phosphatidylinositol-specific phospholipase C from Bacillus cereus in complex with myo-inositol.

Phosphatidylinositol (PI), once regarded as an obscure component of membranes, is now recognized as an important reservoir of second messenger precursors and as an anchor for membrane enzymes. PI-specific phospholipase C (PI-PLC) is the enzyme that cleaves PI, invoking numerous cellular responses. The crystal structure of PI-PLC from Bacillus cereus (EC 3.1.4.10) has been solved at 2.6 A resolution and refined to a crystallographic R factor of 18.7%. The structure consists of an imperfect (beta alpha)8-barrel similar to that first observed for triose phosphate isomerase and does not resemble any other known phospholipase structure. The active site of the enzyme has been identified by determining the structure of PI-PLC in complex with its inhibitor, myo-inositol, at 2.6 A resolution (R factor = 19.5%). This substrate-like inhibitor interacts with a number of residues highly conserved among prokaryotic PI-PLCs. Residues His32 and His82, which are also conserved between prokaryotic and eukaryotic PI-PLCs, most likely act as general base and acid respectively in a catalytic mechanism analogous to that observed for ribonucleases.

Bacillus cereus↗
PubMed1981

Coordinate regulation of gluconeogenesis by the glucocorticoids and glucagon: evidence for acute and chronic regulation by glucagon.

The coordinate regulation of gluconeogenesis by the glucocorticoids and glucagon in primary cultures of adult rat liver parenchymal cells has been studied. The results suggest that glucagon stimulation of glucose production from 3-carbon precursors is composed of at least two components which the glucocorticoids differentially affect. Glucagon treatment of hepatocytes results in an immediate increase in glucose production which is not blocked by cycloheximide and occurs in the absence of any detectable increase of phosphoenolpyruvate carboxykinase activity. This component appears to be regulated by a post-translational mechanism and involves redirection of carbon flow from glycolysis to gluconeogenesis. The second component is characterized by the need for long-term glucagon treatment. This increase in glucose production can be blocked by cycloheximide and is correlated with an increase in phosphoenolpyruvate carboxykinase activity. The reaction that is accelerated by long-term glucagon incubation is located prior to the triose-phosphate level since long-term incubation with glucagon fails to increase glucose production from dihydroxyacetone any more than does short-term incubation. It is suggested that phosphoenolpyruvate carboxykinase rather than amino acid transport is the key pacemaker reaction in the long-term incubation since the direction and magnitude of the response for glucocorticoid and glucagon stimulation of glucose production is the same whether alanine or lactate is used as the 3-carbon precursor. The glucocorticoids exhibit an additive effect on glucagon-stimulated glucose production for the first component whereas they amplify the second component.

Alanine↗