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B Sümegi

Publications and source records attributed to B Sümegi.

18 recordsLinked to original sources
PubMed2003

BGP-15, a hydroximic acid derivative, protects against cisplatin- or taxol-induced peripheral neuropathy in rats.

The neuroprotective effect of BGP-15 against peripheral sensory neuropathy was studied in rats that were exposed to short-term cisplatin or taxol administration. The changes of nerve conduction velocity were determined in situ after treating the Wistar rats with BGP-15 (50, 100, and 200 mg/kg po daily doses throughout the experiment), cisplatin (1.5 mg/kg ip daily dose for 5 days), or taxol (5.0 mg/kg ip daily dose every other day in a 10-day interval) alone or giving the test compound in combination with cisplatin or taxol. Electrophysiological recordings were carried out in vivo by stimulating the sciatic nerve at both sciatic notch and ankle site. Neither motor nor sensory nerve conduction velocity was altered by any dose level of BGP-15 tested. Both anticancer drugs decreased the sensory nerve conduction velocity (SNCV). BGP-15 treatment prevented the impairment of SNCV either in part or totally in the cisplatin- or taxol-treated groups. This neuroprotective potential of BGP-15 could be well correlated with its recently described poly(ADP-ribose) polymerase- inhibitory effect and its ability to protect against the damages induced by the increased level of reactive oxygen species in response to anticancer treatment.

Animals↗
PubMed2001

Homology modelling and molecular dynamics studies of human placental tissue protein 13 (galectin-13).

The primary structure of the newly sequence analysed placental tissue protein 13 (PP13) was highly homologous to several members of the beta-galactoside-binding S-type lectin (galectin) family. By homology modelling, the three-dimensional structure of PP13 was built based on high-resolution crystal structures of homologues and also their characteristic 'jellyroll' fold was found in the case of PP13. Our model has been deposited in the Brookhaven Protein Data Bank. By multiple sequence alignment and structure-based secondary structure prediction, we underlined the structural similarity of PP13 with its homologues. The secondary structure of PP13 was identical with 'proto-type' galectins consisting of a five- and a six-stranded beta-sheet, joined by two alpha-helices, and galectins' highly conserved carbohydrate-recognition domain (CRD) was also present in PP13. Of the eight consensus residues in the CRD, four identical and three conservatively substituted were shared by PP13. By docking simulations PP13 possessed sugar-binding activity with highest affinity to N-acetyllactosamine and lactose typical of most galectins. All ligands were docked into the putative CRD of PP13. Based on several lines of evidence discussed in this paper demonstrating that PP13 is a novel galectin, PP13 was also designated galectin-13. These computational results provide some new insights into the possible role and importance of PP13 in various processes of the human body and can be of help in the initial steps of further functional research.

Amino Acid Sequence↗
PubMed1999

Muscle carnitine acetyltransferase and carnitine deficiency in a case of mitochondrial encephalomyopathy.

Profound decrease of the carnitine acetyltransferase activity (0.08 U/g wet weight; 1.67% of control) and carnitine deficiency (total carnitine was 230 nmol/g wet weight in the patient vs 2730 in the controls) was detected in the skeletal muscle of a female paediatric patient. She died of her illness, which included cerebellar symptoms and slight muscle spasticity affecting mainly the lower extremities, at 1 year of age. Histological examination of the autopsy specimens revealed a selective Purkinje cell degeneration in the cerebellum: the cells had abnormal position, were shrunken and decreased in number, and displayed abnormal dendritic trees and fragmented, disorganized axons. Electron microscopy revealed mitochondrial abnormalities in skeletal and cardiac muscle and also in the Purkinje cells. Deletions of the mitochondrial DNA were detected in the muscle in heteroplasmic form (up to 7%). Mainly the ND4-ND4L region was affected, as evidenced by the PCR; however, other regions of the mitochondrial genome also showed deletions of varying size and extent, suggesting multiple deletions of the mitochondrial DNA.

Brain↗
PubMed1995

[Mitochondrial DNA deletion in hereditary cardio-encephalo-myopathy].

The case of a female patient with cardio-encephalo-myopathy who died of her illness at one year of age, similarly to her three sisters, is reported. In autopsy samples, like muscle, heart, liver and cerebellum activities of several mitochondrial enzymes were determined. In the skeletal muscle serious decrease of carnitine acetyltransferase was observed (from the normal 4.8 U/g to 0.08 U/g wet weight), while in other tissues this activity was normal. In the muscle activities of several other mitochondrial enzymes were also decreased (cytochrome oxidase, NADH cytochrome C oxidoreductase, citrate synthase), while in other tissues there were no similar changes. Serious distortion was observed in the structure of the majority of mitochondria of muscle and heart by electronmicroscopy. The number of the Purkinje-cells in the cerebellum decreased, and the cells were shrunken, their axons were fragmented and disoriented. Also the structure of the mitochondria was abnormal in the Purkinje-cells, while it was normal in other areas of the cerebrum. In te tissues of the patient normal and deleted mitochondrial DNA coexisted as which could explain the genetic background of this disease at molecular level.

Autopsy↗
PubMed1994

[Specific enzyme diagnosis in mitochondrial myopathies and encephalomyopathies].

Mitochondrial enzyme activities (cytochrome c-oxidase = COX, carnitine acyl-transferase = CAT, citrate synthase = CS, lipoamide dehydrogenase = lipDH from the pyruvate-dehydrogenase complex, lactate dehydrogenase = LDH, and malate-dehydrogenase = MDH) were measured from progressive myopathy/encephalomyopathy. Cytochrome oxidase (COX) deficiency was detected from muscle or liver tissues, adult type of COX defectus had been diagnosed in 1 case and infantile type in further 6 cases. The 3 familial atactic children showed decreased activity of carnitine acetyl-transferase, too.

Adolescent↗
PubMed1990

[Cytochrome C oxidase deficiency].

Cytochrome c oxydase deficiency, i.e. a mitochondrial myopathy was diagnosed in a patient suffering from generalized muscle hypotonia. The fatal case presented underlines the importance that within the clinical pattern of myopathies the distinct entities should be differentiated.

Adult↗
PubMed1985

Substrate-induced structural changes of the pyruvate dehydrogenase multienzyme complex.

The time course of the overall reaction catalyzed by the pyruvate dehydrogenase multienzyme complex produces an unexpectedly high lag (tau = 8 S) even in the presence of saturating concentrations of its substrates. The preincubation of the pyruvate dehydrogenase complex with one of the substrates alone decreases the duration of this lag, and all the substrates of the pyruvate dehydrogenase component (E1) and dihydrolipoyl transacetylase component (E2) together (pyruvate, thiamine pyrophosphate, and CoA) result in the complete disappearance of the lag. The reduction of the dihydrolipoyl dehydrogenase component (E3) of the pyruvate dehydrogenase complex with the substrates of the complex in the absence of NAD+ produces significantly different quenching in the FAD fluorescence, and then the reduction with the substrates of E3 as dihydrolipoic acid and dithioerythritol. (The formation of FADH2 was not observed in the system.) The higher fluorescence quenching in the presence of substrates of pyruvate dehydrogenase complex compared to the effect caused by the substrates of the E3 component (dihydrolipoic acid and DTE) indicates conformational changes additionally manifested in the fluorescence properties of the enzyme complex. The substrate-induced quenching of the enzyme-bound FAD fluorescence shows biphasic kinetics. The rate constant of the slow phase is comparable with the rate constant calculated from the time duration of the lag phase observed in the overall reaction. The kinetic analysis of both intensity and anisotropy decrease of the FAD fluorescence suggests a consecutive transmittance of an all substrate-coordinated, induced conformational changes directed from the pyruvate dehydrogenase-via the lipoyl transacetylase--to the lipoyl dehydrogenase. Two simultaneous conformational effects caused by binding of the substrates can be distinguished; one of them results the fluorescence of the bound FAD to be more quenched, while the other makes the FAD more mobile. The first-order rate constants of both these conformational changes were determined. The present observations suggest that the pyruvate dehydrogenase complex exists in a partially inactive state in the absence of its substrates, and it becomes active due to conformational changes caused by the binding of its substrates.

Animals↗
PubMed1983

A study on the physical interaction between the pyruvate dehydrogenase complex and citrate synthase.

In this paper, physicochemical evidence is given for the association between the pyruvate dehydrogenase complex (EC 1.2.4.1) and citrate synthase (EC 4.1.3.7) with two gel chromatographic techniques with poly(ethylene glycol) co-precipitation and with ultracentrifugation. Experiments with active enzyme gel chromatography indicate that citrate synthase also associates with pyruvate dehydrogenase complex in its functioning state. Citrate synthase binds to the isolated transacetylase core of pyruvate dehydrogenase complex, but in the binding to the whole pyruvate dehydrogenase complex the two other components of the complex are also involved. One pyruvate dehydrogenase complex can bind 10-11 citrate synthase dimers, and the dissociation constant is about 5.7-6.0 microM as determined by two independent methods. The association between the pyruvate dehydrogenase complex and citrate synthase raises the possibility of the dynamic compartmentation of acetyl-CoA in the mitochondria which results in the direction of acetyl-CoA from pyruvate towards citrate.

Animals↗
PubMed1983

Association between the alpha-ketoglutarate dehydrogenase complex and succinate thiokinase.

The kinetic parameters of the individual reaction of pig heart alpha-ketoglutarate dehydrogenase complex, succinate thiokinase and the alpha-ketoglutarate dehydrogenase complex-succinate thiokinase coupled system were studied. The KCoAm of alpha-ketoglutarate dehydrogenase complex and the K-succinyl CoAm of succinate thiokinase decreased in the coupled system when compared to those of the individual enzyme reactions. This phenomenon can be explained by the interaction between the alpha-ketoglutarate dehydrogenase complex and succinate thiokinase. By means of poly(ethylene glycol) precipitation, ultracentrifugation and gel chromatography we were able to detect a physical interaction between the alpha-ketoglutarate dehydrogenase complex and succinate thiokinase. Of the seven investigated proteins only succinate thiokinase showed association with alpha-ketoglutarate dehydrogenase complex. On the other hand, succinate thiokinase did not associate with other high molecular weight mitochondrial enzymes such as pyruvate dehydrogenase complex and glutamate dehydrogenase. On this basis, the interaction between succinate thiokinase and alpha-ketoglutarate dehydrogenase complex was assumed to be specific. These in vitro data raise the possibility that a portion of the citric acid cycle enzymes exists as a large multienzyme complex in the mitochondrial matrix.

Animals↗
PubMed1983

Elementary steps in the reaction of the pyruvate dehydrogenase complex from pig heart. Kinetics of thiamine diphosphate binding to the complex.

In the progress curve of the reaction of the pyruvate dehydrogenase complex, a lag phase was observed when the concentration of thiamin diphosphate was lower than usual (about 0.2-1 mM) in the enzyme assay. The length of the lag phase was dependent on thiamin diphosphate concentration, ranging from 0.2 min to 2 min as the thiamin diphosphate concentration varied from 800 nM to 22 nM. The lag phase was also observed in the elementary steps catalyzed by the pyruvate dehydrogenase component. A Km value of 107 nM was found for thiamin diphosphate with respect to the steady-state reaction rate following the lag phase. The pre-steady-state kinetic data indicate that the resulting lag phase was the consequence of a slow holoenzyme formation from apoenzyme and thiamin diphosphate. The thiamin diphosphate can bind to the pyruvate dehydrogenase complex in the absence of pyruvate, but the presence of 2 mM pyruvate increases the rate constant of binding from 1.4 X 10(4) M-1 S-1 to 1.3 X 10(5) M-1 S-1 and decreases the rate constant of dissociation from 2.3 X 10(-2) S-1 to 4.1 X 10(-3) S-1. On the other hand, the effect of pyruvate on the thiamin diphosphate binding revealed the existence of a thiamin-diphosphate-independent pyruvate-binding site in the pyruvate dehydrogenase complex. Direct evidence was also obtained with fluorescence techniques for the existence of this binding site and the dissociation constant of pyruvate was found to be 0.38 mM. On the basis of these data we have proposed a random mechanism for the binding of pyruvate and thiamin diphosphate to the complex. Binding of substrates to the enzyme complex caused an increase in the fluorescence of the dansylaziridine-labelled pyruvate dehydrogenase complex, showing that binding of substrates to the complex is accompanied by structural changes.

Animals↗
PubMed1983

Paracatalytic inactivation of pig heart pyruvate dehydrogenase complex.

The phenomenon of paracatalytic inactivation has been demonstrated and characterized with the pig heart pyruvate dehydrogenase complex. The enzyme became progressively inactive when it was preincubated in the presence of pyruvate, thiamine pyrophosphate, and extrinsic oxidative agent, 2,6-dichloroindophenol. Not only the overall reaction of enzyme complex but the individual reactions catalyzed by enzyme components, pyruvate dehydrogenase, and dihydrolipoamide acetyltrasferase, were reduced after preincubation. The observed inactivation is due to two factors: (i) covalent incorporation of the pyruvate atoms, and (ii) formation of a thiamine pyrophosphate analog. (i) A covalent incorporation of radioactivity from [2-14C]pyruvate into the enzyme complex, which was proportional to the inhibition of overall reaction was observed. Seventy-eight percent of the radioactivity incorporated into the dihydrolipoamide transacetylase but not into the lipoic acid. Thus, modification of the dihydrolipoamide acetyltransferase component can be attributed to the covalent incorporation of pyruvate atoms. (ii) During inactivation, the enzyme-bound thiamine pyrophosphate underwent a modification resulting in the formation of a thiamine pyrophosphate analog, presumably thiamine thiazolone pyrophosphate, which inhibited exclusively the pyruvate dehydrogenase component.

2,6-Dichloroindophenol↗
PubMed1982

Diacetyl: a new substrate in the overall reaction of the pyruvate dehydrogenase complex.

Pig heart pyruvate dehydrogenase complex (pyruvate: lipoamide oxidoreductase (decarboxylating and acceptor-acetylating), EC 1.2.4.1) catalyzes the decomposition of diacetyl to acetate, acetyl-CoA and produces reduced NAD+ with 1:1:1 stoichiometry. The reaction rate with diacetyl is approximately 7.1% of that with pyruvate. The Km value for diacetyl was found to be 0.46 mM. Acetoin and acetaldehyde inhibit the pyruvate dehydrogenase-catalyzed reaction of diacetyl with Ki values of 0.91 mM and 0.48 mM, respectively. Inhibition patterns show that they are competitive inhibitors versus diacetyl. Acetate, as product, does not inhibit the enzymatic decomposition of diacetyl. Diacetyl is not only an alternative substrate in the pyruvate dehydrogenase reaction, but a competitive inhibitor versus pyruvate with a Ki value of 0.43 mM.

Acetaldehyde↗
PubMed1980

Interaction between the pyruvate dehydrogenase complex and citrate synthase.

Kinetic studies of the individual reaction of pig heart pyruvate dehydrogenase complex (pyruvate dehydrogenase (pyruvate:lipoamide oxidoreductase (decarboxylating and acceptor-acetylating), EC 1.2.4.1); dihydrolipoamide reductase(NAD+) (NADH:lipoamide oxidoreductase, EC 1.6.4.3); dihydrolipoamide acetyltransferase (acetyl-CoA:dihydrolipoamide S-acetyltransferase, EC 2.3.1.12)), citrate synthase (citrate oxaloacetate-lyase (pro-3S-CH2COO- leads to acetyl-CoA), EC 4.1.3.7) and the pyruvate dehydrogenase complex-citrate synthase coupled system show that the KmCoA value of pyruvate dehydrogenase complex and KmCoASAc value of citrate synthase decrease in the coupled system when compared to those in the individual enzyme reactions. The explanation for this interaction may be an association between the two enzymes. When it was centrifuged with 150 000 x g for 140 min, 30% of the citrate synthase sedimented in the presence of the pyruvate dehydrogenase complex, while no sedimentation was observed in the absence of the pyruvate dehydrogenase complex. Sedimentation of cytoplasmic malate dehydrogenase, phosphotransacetylase, hemoglobin and Blue albumin were negligible under the same condition. In gel chromatography experiments a significant peak of citrate synthase activity co-migrated with the pyruvate dehydrogenase complex peak. This observation also suggests the possible association of two enzymes.

Animals↗
PubMed1978

Demonstration of a lag period in the time-course of the reaction catalyzed by pyruvate dehydrogenase complex.

At low thiamine pyrophosphate concentrations the time-course of the reaction catalyzed by mammalian pyruvate dehydrogenase complex shows a lag period of some minutes when the reaction is started by either enzyme, pyruvate or thiamine pyrophosphate. However, started by CoASH or NAD+, the lag period disappears. An increase in enzyme concentration to 25 mU/ml causes a concomitant shortening of the duration of the lag period (tau), while above this value tau is independent of the enzyme concentration. An increase in thiamine pyrophosphate concentration decreases the value of tau and the lag period vanishes at infinite thiamine pyrophosphate concentration. It is suggested that both isomerization and aggregation-dissociation reactions may play an improtant role in the development of the lag period of pyruvate dehydrogenase complex.

Animals↗
PubMedDate not supplied

Molecular cloning and characterization of placental tissue protein 18 (PP18a)/human mitochondrial branched-chain aminotransferase (BCATm) and its novel alternatively spliced PP18b variant.

Five different insert-length cDNAs encoding for soluble placental tissue protein 18 (PP18) variants were isolated by screening a human placental cDNA library using monospecific anti-PP18 serum. Sequence analysis of the longest clone showed that the insert contains an open reading frame encoding for a 392 residue-long protein with a 27 amino acid mitochondrial targeting sequence. The mature protein-designated PP18a-is 41.264 kDa consisting of 365 residues and is identical to the previously isolated and characterized PP18 antigen described in 1985. We also found a new, alternatively spliced cDNA encoding for a 300 residue-long, 33.776 kDa protein, which was designated PP18b. Alignment search of the protein databank showed that PP18a is almost entirely identical to the human mitochondrial branched-chain aminotransferase, while PP18b is its newly discovered splicing variant. We detected the two PP18 variants in normal adult and fetal human tissues besides the mitochondrial (only PP18a) and cytosolic (only PP18b) fractions of term placenta with chemiluminescence Western blot analysis. The 41 kDa PP18a variant was expressed ubiquitously, while the 33 kDa PP18b variant was found in smaller amounts in nearly all tissues. Trace amounts of the variants were present in the sera of non-pregnant healthy controls, as well as in pregnant women, but there was no real change in serum levels during pregnancy. In conclusion, PP18 variants are not specific for the placenta. Aminotransferase activity of placental origin PP18 antigens was verified by structural analysis and by a coupled branched-chain aminotransferase/glutamate dehydrogenase assay.

Alternative Splicing↗
PubMedDate not supplied

Overexpression of placental tissue protein 17b/TIP47 in cervical dysplasias and cervical carcinoma.

In our previous Western- and Northern-blot investigations, high over-expression of placental protein 17b/TIP47 was detected in extracts of human cervical carcinoma tissues compared to normal conditions of the cervical tissue. PP17b serum levels were also elevated in untreated cervical carcinoma patients compared to healthy controls. In the present study, the expression pattern of PP17 proteins was investigated in various cervical dysplasias and in cervical carcinoma tissue specimens by the streptavidin-biotin immunoperoxidase technique using PP17-specific antiserum. In normal third-trimester human placentas, which served as positive controls, mainly cytoplasmic PP17 immunostaining of syncytiotrophoblasts and chorionic trophoblasts was observed. Normal human uterine cervical squamous and glandular epithelia were negative or weakly positive, while in low grade dysplasias (CIN I-II) only the cytoplasms of dysplastic cells were weakly positive or positive; in high grade dysplasias (CIN III/ISC) cytoplasms of the dysplastic cells were strongly positive. Normal and superficial cells in the differentiated zones were negative in all tissue specimens. In cases of invasive epithelial cervical carcinomas, small basal-type tumour cells were mostly negative whilst cells with squamous differentiation were strongly positive for PP17. Our hypotheses for this newly detected phenomenon are briefly discussed.

Adult↗