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S Ghisla

Publications and source records attributed to S Ghisla.

At least 73 records · Page 4Linked to original sources
PubMed1992

Prostaglandin 9-ketoreductase from pig and human kidney: purification, properties and identity with human carbonyl reductase.

Prostaglandin 9-ketoreductase has been purified to apparent homogeneity from pig and human kidney with an overall yield of 6%. The enzyme has a molecular mass of 34 kDa, it is present as an active monomer in diluted solution and contains approx. 2 equivalents Zn++/mole enzyme. It is stereoselective for the pro(S) hydrogen of NADPH and reduces the prostaglandin 9-keto group to yield 90% prostaglandin F2 alpha and 8% of the beta-form. An extensive study of the catalytic properties was carried out, which leads to the conclusion that the enzyme function in vivo is unlikely a catalysis of oxidation/reduction at the prostaglandin 9-position. Five peptides from the pig kidney enzyme were sequenced and compared with the sequence of carbonyl reductase from human placenta. The identity is > 90% and this, together with the immunological cross-reactivity with human brain carbonyl reductase, most strongly suggests that prostaglandin 9-ketoreductase and carbonyl reductase are the same enzyme.

Alcohol Oxidoreductases↗
PubMed1991

Structural, spectroscopic and catalytic activity studies on glutathione reductase reconstituted with FAD analogues.

FAD-modified human glutathione reductases were reconstituted from apoenzyme using the FAD analogues 6-SH-FAD, 6-SCN-FAD, 6-OH-FAD, 6-NH2-FAD and 8-OH-FAD. The catalytic activities of the modified enzymes were substantially lower than for the native enzyme. All five species could be crystallized, but only those containing 6-SH-FAD, 6-OH-FAD and 6-NH2-FAD yielded crystals that could be analyzed. X-ray analyses and structural refinements were performed at 0.27 nm and 0.30 nm resolution resulting in R factors around 13.5%. The crystal structures showed the additional non-hydrogen atoms and small conformational changes of the polypeptide that were obviously induced by the substituents of the FAD analogues. The observed changes together with spectroscopic and activity data permit some conclusions about the chemical nature of the substituents.

Catalysis↗
PubMed1991

Structurally different rat liver medium-chain acyl CoA dehydrogenases directed by complementary DNAs differing in their 5'-region.

Different forms of rat liver medium-chain acyl CoA dehydrogenase (MCAD) (EC 1.3.99.3) were produced in Escherichia coli carrying expression plasmids (pRMCADm-1 approximately 9) differing at the 5'-region of the cDNA. The proteins expressed could be readily extracted from the cells. The protein (approximately 44 kDa) directed by pRMCADm-3 showed the highest activity and was readily purified to homogeneity. The purified enzyme contained non-covalently bound FAD and was similar to rat liver mitochondrial enzyme in all respects examined. The purified protein (approximately 45 kDa) directed by pRMCADm-1 did not contain FAD and showed no enzymatic activity. Therefore, the leader peptide disturbs the binding of FAD to the apoprotein. The purified protein (approximately 40 kDa) directed by pRMCADm-6 did not contain FAD. Thus, the deletion of the NH2-terminal portion of the apoprotein to some extent results in its inability to combine with FAD.

Acyl-CoA Dehydrogenase↗
PubMed1991

Metabolic consequences of methylenecyclopropylglycine poisoning in rats.

We describe the effects of methylenecyclopropylglycine in fasted rats. A 75% decrease in the blood glucose concentration and an increase of lactate and pyruvate were observed 6 h after administration of 100 mg of this amino acid/kg. By contrast with the effects reported for hypoglycin [Williamson & Wilson (1965) Biochem. J. 94, 19c-21c], the plasma concentrations of ketone bodies decreased after administration of methylenecyclopropylglycine and the concentrations of branched-chain amino acids in the plasma were increased 6-fold. The oxidation of decanoylcarnitine or of palmitate was nearly completely inhibited in rat liver mitochondria from methylenecyclopropylglycine-poisoned rats. The activities of acetoacetyl-CoA and of 3-oxoacyl-CoA thiolase were decreased to 25% and less than 10% of the controls. There was a pronounced aciduria, due to the excretion of dicarboxylic acids and of oxidation products of branched-chain amino acids. The accumulation of the toxic metabolite methylenecyclopropylformyl-CoA in the mitochondrial matrix was detected after administration of methylenecyclopropylglycine. Similarly we confirmed experimentally that methylenecyclopropylacetyl-CoA accumulates in mitochondria incubated with methylenecyclopropylpyruvate.

Acyl Coenzyme A↗
PubMed1990

7-Substituted pterins: formation during phenylalanine hydroxylation in the absence of dehydratase.

Previously we described a new form of human hyperphenylalaninemia characterized by the formation of 7-substituted pterins. We present evidence strongly suggesting that the 7-substituted pterins are formed by rearrangement of 6-substituted pterins. This rearrangement occurs during the phenylalanine hydroxylase reaction cycle which normally involves the enzymes phenylalanine hydroxylase, pterin-4a-OH-dehydratase, and q-dihydropterin reductase, specifically in the absence of dehydratase activity. We conclude that formation of 7-substituted pterins in humans is a consequence of an absence of dehydratase activity, which might result from a genetic defect. A chemical mechanism for this rearrangement is presented. Our results also suggest that tetrahydroneopterin can be a cofactor for the phenylalanine hydroxylase system in vivo.

Animals↗
PubMed1990

2-Aminobenzoyl-CoA monooxygenase/reductase, a novel type of flavoenzyme. Identification of the reaction products.

In a previous report we have described some properties of a novel flavoenzyme from a denitrifying Pseudomonas species which catalyzes the oxygen- and NAD(P)H-dependent conversion of 2-aminobenzoyl-CoA [Buder, R., Ziegler, K., Fuchs, G., Langkau, B. & Ghisla, S. (1989) Eur. J. Biochem. 185, 637-634]. In this paper, we report on the identification of the three products formed from 2-aminobenzoyl-CoA in this reaction. The spectroscopic data and the chemical properties of these compounds and those of their degradation products are compatible with the structures of 2-amino-5-hydroxybenzoyl-CoA, 2-amino-5-hydroxycyclohex-1-enecarboxyl-CoA and of 2-amino-5-oxocyclohex-1-enecarboxyl-CoA. The latter is the main product and was found to be rather unstable since it hydrolyzes and decarboxylates readily at pH less than 5. Ammonia is released from the decarboxylation product in the neutral pH range to yield 1,4-cyclohexanedione. Conditions were optimized such that the CoA thioester of 2-amino-5-hydroxybenzoate is the product obtained at greater than 98% yield. 2-amino-5-hydroxycyclohex-1-enecarboxyl-CoA is the product which is formed when the mixture of the reaction products is treated with sodium borohydride before separation.

Chemical Phenomena↗
PubMed1990

Characterization of wild-type and an active site mutant of human medium chain acyl-CoA dehydrogenase after expression in Escherichia coli.

The cDNA of human medium chain acyl-CoA dehydrogenase (MCADH) was modified by in vitro mutagenesis, and the sequence encoding the mature form of MCADH was introduced into an inducible expression plasmid. We observed synthesis of the protein in Escherichia coli cells transformed with this plasmid with measurable MCADH enzyme activity in cell extracts. Glutamic acid 376, which has been proposed by Powell and Thorpe (Powell, P. J., and Thorpe, J. (1988) Biochemistry 27, 8022-8028) as an essential residue and the proton-abstracting base at the active site of the enzyme, was mutated to glutamine. After expression in bacteria of this plasmid, the corresponding extracts show no detectable MCADH activity, although mutant MCADH-protein production was detected by protein immunoblots. The mature enzyme and the Gln376 mutant were purified to apparent homogeneity. The wild-type enzyme is a yellow protein due to the content of stoichiometric FAD and had a specific activity which is 50% of MCADH purified from pig kidney. The Gln376 mutant is devoid of activity (less than 0.02% that of wild type, expressed enzyme) and is green because of bound CoA persulfide. Properties of the mutant enzyme suggest that the Glu376----Gln change specifically affects substrate binding. These results prove that Glu376 plays an important role in the initial step of dehydrogenation catalysis.

Acyl-CoA Dehydrogenase↗
PubMed1990

1H-NMR and mass spectrometric studies of tetrahydropterins. Evidence for the structure of 6-pyruvoyl tetrahydropterin, an intermediate in the biosynthesis of tetrahydrobiopterin.

The conversion of dihydroneopterin triphosphate in the presence of 6-pyruvoyl tetrahydropterin synthase was followed by 1H-NMR spectroscopy. The interpretation of the spectra of the product is unequivocal: they show formation of a tetrahydropterin system carrying a stereospecifically oriented substituent at the asymmetric C(6) atom. The spectra are compatible with formation of a (3')-CH3 function, and with complete removal of the 1' and 2' hydrogens of dihydroneopterin triphosphate. The fast-atom-bombardment/mass spectrometry study of the same product yields a [M + H]+ ion at m/z 238 compatible with the structure of 6-pyruvoyl tetrahydropterin. The data support the proposed structure of 6-pyruvoyl tetrahydropterin as a key intermediate in the biosynthesis of tetrahydrobiopterin.

Alcohol Oxidoreductases↗
PubMed1990

A time-dependent bacterial bioluminescence emission spectrum in an in vitro single turnover system: energy transfer alone cannot account for the yellow emission of Vibrio fischeri Y-1.

Yellow fluorescent protein (YFP), which has a bound FMN, was isolated from the marine bacterium Vibrio fischeri strain Y-1b. Its presence in a luciferase [alkanal monooxygenase (FMN-linked); alkanal, reduced-FMN:oxygen oxidoreductase (1-hydroxylating, luminescing), EC 1.14.14.3] reaction mixture causes a striking color change, and an increase in bioluminescence intensity, as well as a faster rate of intensity decay, so that the quantum yield is not changed. The emission spectrum shows two distinct color bands, one at 490 nm attributed to the unaltered emission of the luciferase system, the other peaking in the yellow around 540 nm due to YFP emission. The kinetics of the two color bands differ, so the spectrum changes with time. The yellow emission reaches its initial maximum intensity later than the blue, and then both blue and yellow emissions decay exponentially with nearly the same pseudo-first-order rate constants, linearly dependent on [YFP] (from 0.01 sec-1 with no YFP to a maximum of approximately 0.1 sec-1 at 4 degrees C) but exhibiting a saturation behavior. The data can be interpreted by assuming the interaction of YFP with the peroxyhemiacetal intermediate in the luciferase reaction to form an unstable new complex whose breakdown gives the yellow emitter in its excited state. This simple model fits well the data at [YFP] less than 15 microM. The results indicate that a single primary excited state cannot be responsible for the blue and the yellow emissions.

Bacterial Proteins↗
PubMed1989

2-Aminobenzoyl-CoA monooxygenase/reductase, a novel type of flavoenzyme. Studies on the stoichiometry and the course of the reaction.

The reaction catalyzed by 2-aminobenzoyl-coenzyme-A monooxygenase/reductase from a denitrifying Pseudomonas sp. has been investigated. 2-Aminobenzoyl-CoA and 2-amino[carboxy-14C]benzoyl-CoA were synthesized enzymatically using 2-aminobenzoyl-CoA synthetase from the same organism. The product was purified by chromatography and characterized by ultraviolet/visible and 1H-NMR spectroscopy. The conversion of 2-aminobenzoyl-CoA catalyzed by the monooxygenase/reductase requires NADH and oxygen, and yields at least two different products depending on the relative concentration of NADH. At [NADH] less than Km (40 microM), i.e. [NADH]/[2-aminobenzoyl-CoA] approximately 0.02-0.05, the main product is probably a hydroxylated derivative of 2-aminobenzoyl-CoA, which is characterized by an absorbance maximum around 375 nm. When [NADH]/[2-aminobenzoyl-CoA] approximately 2-5, the predominant product is a non-aromatic coenzyme A thioester (lambda max approximately 320 nm). The stoichiometry in this case is 2.1-2.4 mol NADH oxidized (mol oxygen consumed)-1 (mol 2-aminobenzoyl-CoA metabolized)-1. The product is extremely unstable in the acidic pH range and undergoes decarboxylation in a few minutes at pH less than 5. Some degree of stabilisation is obtained upon reduction with sodium borohydride, probably resulting in a further reduced non-aromatic coenzyme-A thioester.

Catalysis↗
PubMed1989

Mechanism of hypoglycaemic action of methylenecyclopropylglycine.

The effects of methylenecyclopropylglycine (MCPG), the lower homologue of hypoglycin A, on starved rats are described. Upon oral ingestion of MCPG (43 mg/kg), a 50% decrease in blood glucose compared with controls was observed after 4 h. The plasma concentrations of lactate and non-esterified fatty acids were substantially increased during this period. The activity of general acyl-CoA dehydrogenase from isolated rat liver mitochondria was not significantly changed. By contrast, the activity of 2-methyl-(branched-chain)-acyl-CoA dehydrogenase decreased by over 80%. The enzyme activity of enoyl-CoA hydratase (crotonase) from pig kidneys decreased by 80% on incubation with the hypothetically toxic metabolite of MCPG, methylenecyclopropylformyl-CoA. These results suggest that the inhibition spectrum of MCPG is quite different from that of hypoglycin A and that similar physiological effects might result from inhibition of different enzymes of beta-oxidation, e.g. hypoglycaemia and lacticacidemia. Accumulation of medium-chain acyl-CoA thioesters is probably at the origin of disturbances in pyruvate metabolism.

Acyl-CoA Dehydrogenases↗
PubMed1989

Bioluminescence emission of bacterial luciferase with 1-deaza-FMN. Evidence for the noninvolvement of N(1)-protonated flavin species as emitters.

The reaction of reduced 1-d-FMN with oxygen and decanal results in bioluminescence with kinetic and spectral properties similar to those of the reaction with FMNH2, even though the spectral (absorbance, fluorescence) and chemical properties of the oxidized forms differ greatly. This emission, which is about 10-15% as efficient as with FMNH2, is postulated to involve the intermediacy of the corresponding 4a-hydroperoxide, the fluorescence of which occurred transiently. The N(1) protonated species had been proposed as the emitter in the reaction with FMNH2, but the 1-deaza analog cannot be protonated at the corresponding position, thus excluding this possibility.

Flavin Mononucleotide↗
PubMed1989

Mechanisms of flavoprotein-catalyzed reactions.

Flavoproteins are a class of enzymes catalyzing a very broad spectrum of redox processes by different chemical mechanisms. This review describes the best studied of these mechanisms and discusses factors possibly governing reactivity and specificity.

Flavins↗
PubMed1988

Oxidation-reduction of general acyl-CoA dehydrogenase by the butyryl-CoA/crotonyl-CoA couple. A new investigation of the rapid reaction kinetics.

Pig kidney general acyl-CoA dehydrogenase (GAD) can be reduced by butyryl-CoA to form reduced enzyme and crotonyl-CoA. This reaction is reversible. Stopped-flow, kinetic investigations on GAD have been made, using the following reaction pairs: oxidized GAD/butyryl-CoA, oxidized GAD/crotonyl-CoA, oxidized GAD/alpha,beta-dideuteriobutyryl-CoA, reduced GAD/butyryl-CoA, and reduced GAD/crotonyl-CoA (in 50 mM potassium phosphate buffer, pH 7.6 at 4 degrees C). Reduction of GAD by butyryl-CoA is triphasic. The slowest phase is 100-fold slower than the preceding phase and appears to represent a secondary process not directly related to the primary reduction events. The first two fast phases are responsible for reduction of GAD. Reduction proceeds via a reduced enzyme/crotonyl-CoA charge-transfer complex. alpha, beta-Dideuteriobutyryl-CoA elicits a major deuterium isotope effect (15-fold) on the reduction reaction. Oxidation of GAD by crotonyl-CoA is biphasic. Oxidation proceeds via the same reduced enzyme/crotonyl-CoA charge-transfer complex seen during reduction. The oxidation reaction ends in a mixture composed largely of oxidized GAD species. From the data, we constructed a mechanism for the reduction/oxidation of GAD by butyryl-CoA/crotonyl-CoA. This mechanism was then used to simulate all of the observed kinetic time course data, using a single set of kinetic parameters. A close correspondence between the observed and simulated data was obtained.

Acyl Coenzyme A↗