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Biomedical subjects

B Pensa

Publications and source records attributed to B Pensa.

At least 19 recordsLinked to original sources
PubMed1994

Selenomethionine as substrate for glutamine transaminase.

Selenomethionine is as a good substrate as methionine for bovine liver glutamine transaminase (E.C. 2.6.1.15). Almost identical Km values for methionine, selenomethionine, 4-methylthio-2-oxobutanoic acid and 4-methylseleno-2-oxobutanoic acid have been obtained. Like for other enzymes, also for glutamine transaminase the substitution of the sulfur atom in a substrate molecule by a selenium one does not appreciably affect the enzyme affinity. Glutamine transaminase may thus be involved in selenomethionine catabolism.

Animals↗
PubMed1993

The inhibition of bovine serum amine oxidase by cysteamine.

Bovine serum amine oxidase (BSAO) is inhibited by cysteamine, while cystamine is a good substrate. The activity of BSAO is not restored following removal of excess cysteamine by N-ethylmaleimide, by iodoacetate or by filtration through a G-25 Sephadex column.

Animals↗
PubMed1992

Transamination of some sulphur- or selenium-containing amino acids by bovine liver glutamine transaminase.

S-(3-aminopropyl)cysteine and Se-(3-aminopropyl)selenocysteine are deaminated by bovine liver glutamine transaminase. The corresponding alpha-keto acids, S-(3-aminopropyl)-thiopyruvic acid and Se-(3-aminopropyl)selenopyruvic acid, are produced which spontaneously cyclize to ketimine derivatives. They have been identified by comparing their UV absorption spectra and some chemical or chromatographic properties with chemically synthesized authentic samples. Also S-(2-aminoethyl)homocysteine is the substrate for the enzyme. Kinetic parameters determined in comparison to thialysine and selenalysine show that neither the presence of a sulphur or a selenium atom nor the relative position of the atom in the carbon chain appreciably affects the substrate specificity of the enzyme. However, the length of the carbon chain has some influence on it.

Amino Acids↗
PubMed1991

Sulfur-containing cyclic ketimines and imino acids. A novel family of endogenous products in the search for a role.

Aminoethylcysteine, lanthionine, cystathionine and cystine are mono-deaminated either by L-amino-acid oxidase or by a transaminase exhibiting the properties described for glutamine transaminase. The deaminated products cyclize producing the respective ketimines. Authentic samples of each ketimine were prepared by reacting the appropriate aminothiol compound with bromopyruvate, except cystine ketimine which required the interaction of thiopyruvate with cystine sulfoxide. Reduction of the first three mentioned ketimines with NaBH4 yields the respective derivatives with the saturated rings of thiomorpholine and hexahydrothiazepine. The same reduction is carried out enzymically by a reductase extracted from mammalian tissues. Properties of the members of this family of compounds are described. Gas chromatography followed by mass spectrometry permits the identification of most of these products. HPLC is very useful for the determination of the ketimines by taking advantage of specific absorbance at 380 nm obtained by prior derivatization with phenylisothiocyanate. Adaptation of these and other analytical procedures to biological samples disclosed the presence of most of these compounds in bovine brain and in human urine. By using [35S]lanthionine ketimine as a representative member of the ketimine group, the specific, high-affinity, saturable and reversible binding to bovine brain membranes has been demonstrated. The binding is removed by aminoethylcysteine ketimine and by cystathionine ketimine indicating the occurrence in bovine brain of a common binding site for ketimines. The reduced ketimines are totally ineffective in competing with [35S]lanthionine ketimine. Alltogether these findings are highly indicative for the existence in mammals of a novel class of endogenous sulfur-containing cyclic products provided with a possible neurochemical function to be investigated further.

Amino Acids, Sulfur↗
PubMed1989

Selenalysine transamination by a bovine brain enzyme.

Selenalysine is deaminated by glutamine transaminase from bovine brain, leading to the production of the corresponding alpha-ketoacid, which spontaneously cyclizes to a ketimine form. Selenalysine shows a good affinity for the enzyme.

Animals↗
PubMed1986

Transamination of L-cystathionine and related compounds by a bovine liver enzyme. Possible identification with glutamine transaminase.

A transaminase which catalyses the monodeamination of L-cystathionine was purified 1100-fold with a yield of 15% from bovine liver. The monoketoderivative of cystathionine spontaneously produces the cyclic ketimine. Other sulfur-containing amino acids related to cystathionine such as cystine, lanthionine and aminoethylcysteine were also substrates for the enzyme. The relative molecular mass of the enzyme was determined to be 94 000 with a probable dimeric structure formed of identical subunits. The isoelectric point of the enzyme was at pH 5.0 and the maximal enzymatic activity was found at pH 9.0--9.2. Kinetic parameters for cystathionine and for the other sulfur amino acids as well as for some alpha-keto acids were also determined. Among the natural amino acids tested, glutamine, methionine and histidine were the best amino donors. The enzyme exhibited maximal activity toward phenylpyruvate and alpha-keto-gamma-methiolbutyrate as amino acceptors. The broad specificity of the enzyme leads us to infer that the cystathionine transaminase is very similar or identical to glutamine transaminase.

Amino Acids↗
PubMed1985

Determination of 3-mercaptolactic acid by amino acid analyzer after aminoethylation.

A quantitative determination of 3-mercaptolactic acid was performed after its conversion into S-aminoethylmercaptolactic acid by reacting with excess of 2-bromoethylamine. S-aminoethylmercaptolactic acid was quantitated by an amino acid analyzer. Other thiols were shown not to interfere with the determination of 3-mercaptolactic acid. The sensitivity of the method was at the nanomoles level. The application of the method to the determination of 3-mercaptolactic acid in human urine is also reported.

Amino Acids, Sulfur↗
PubMed1985

The conversion of L-cystathionine into the cyclic ketimine form by heated rat liver extracts containing cystathionase and transaminase activities.

Rat liver homogenates heated for 10 min at 60 degrees C incubated with L-cystathionine yield cystathionine ketimine which was identified by its typical UV spectrum and by cochromatography with authentic samples on the amino acid analyzer. Alanine and alpha-amino butyric acid have been also detected among the final products. The reaction is due to heat stable gamma-cystathionase and transaminases present in the extracts. Cystathionase produces alpha-keto butyric acid and pyruvic acid which are then used for the transamination of the remaining cystathionine to yield the ketimine. This is the first report indicating the occurrence in a mammalian tissue of an enzymatic system using cystathionine for reactions differing from the traditional transulfuration to cysteine.

Animals↗
PubMed1985

New enzymatic changes of L-cystathionine catalyzed by bovine tissue extracts.

L-Cystathionine was used as substrate for enzyme systems prepared by heating bovine tissue extracts in the presence of pyruvate at 60 degrees C for 10 min. Analysis of the products indicated that the systems converted L-cystathionine into the cyclic ketimine form which was detected by its spectral properties and by chromatography on the amino acid analyzer. Alanine, alpha-aminobutyrate and cystine were also produced. Pyruvate and alpha-ketobutyrate enhance the production of the ketimine by liver, kidney and heart extracts, and are necessary for the brain extracts: alpha-Ketoglutarate is much less effective and its presence favors the production of homocystine by all the extracts. Homocystine was found in the brain incubates when any of the ketoacids assayed were added. The overall reaction is explained by the action of heat stable cystathionine gamma-lyase and beta-synthase which produce alpha-ketobutyrate and pyruvate used for the transamination of the remaining cystathionine to the monoketoacid. This last compound cyclizes spontaneously into the ketimine form thus avoiding the removal of the second amino group. This represents a new nontransulfurative path leading to the production of a seven membered etherocyclic product whose biochemical implications are yet unexplored.

Amino Acids↗
PubMed1982

Reduction of beta-thiopyruvic acid by lactate dehydrogenase: a kinetic study.

In this paper a steady-state kinetic study on the system lactate dehydrogenase-beta-thiopyruvate-beta-thiolactate is presented and the possible mechanistic and physiological implications are discussed. At pH 7.4 the equilibrium between beta-thiopyruvate and beta-thiolactate, in the presence of NADH and lactate dehydrogenase is largely shifted towards the formation of beta-thiolactate as in the case of pyruvate and lactate. This can can be relevant in connection with the mixed disulfide between cysteine and beta-thiolactate that is observed to be present in the mammalian body fluids. The catalytic mechanism is of the bi-bi compulsory type, and rapid equilibrium conditions for the binding of the first substrate (NADH) are shown to apply. A complex inhibition pattern of inhibitions by both substrates, however, prevents simple suggestions about the nature of the dead-end species involved.

Binding, Competitive↗
PubMed1982

Preparation of 3-mercaptolactic acid and S-aminoethylmercaptolactic acid.

A simple and accurate method is described for synthesis of 3-mercaptolactic acid and its derivative, S-aminoethylmercaptolactic acid. Some spectrometric data of compounds are reported as well as their melting points, some colorimetric reactions and thin layer chromatographic behaviour. S-Aminoethylmercaptolactic acid is also determined by amino acid analyzer.

Amino Acids, Sulfur↗
PubMed1981

Multiple forms of bovine liver rhodanese.

The heterogeneity of crystalline rhodanese from bovine liver has been studied. The enzyme was separated by preparative disc electrophoresis into four stable forms designated I(3.5%), II(17.0%), III(62.0%) and IV(17.5%). All these components have the same molecular weight of about 35,000 both in native and denaturing conditions. No differences in the primary structure have been detected in amino acid composition and by peptide mapping. Although the isolated forms show similar values of specific activity, except form I, their content of transferable sulfur is different. The enzyme-sulfur complexes of the four components have slightly different circular dichroism spectra in the near ultraviolet, though their spectra in the sulfur-free state are identical. We conclude that these forms are conformational isomers originated from form IV which is predominant in the mitochondrial extract of liver cells.

Animals↗
PubMed1980

Cyanylation of rhodanese by 2-nitro-5-thiocyanobenzoic acid.

Cyanylation of rhodanese (thiosulfate:cyanide sulfurtransferase, EC 2.8.1.1) with a nearly stoichiometric amount of 2-nitro-5-thiocyanobenzoic acid produces a modification of the essential sulfhydryl group. Different S-cyano derivatives are obtained with the enzyme intermediate bearing transferable sulfur bound as a persulfide group (sulfur-rhodanese: E-S-SH) and with the sulfur-free rhodanese (E-SH). The interaction of a neighboring sulfhydryl group splits thiocyanate from the sulfur-rhodanese derivative and cyanide from the sulfur-free rhodanese derivative. In both cases an intramolecular disulfide bond is formed. Iodoacetate is effective on the modified enzyme only after cyanide addition which splits the disulfide so that the essential sulfhydryl group can be alkylated.

Animals↗
PubMed1977

Selective reactivity of rhodanese sulfhydryl groups with 5,5'-dithio-bis(2-nitrobenzoic acid).

The reactivity of the sulfhydryl groups of sulfur-containing and sulfur-free rhodanese (thiosulfate : cyanide sulfurtransferase, EC 2.8.1.1) with 5,5'-dithio-bis(2-nitrobenzoic acid) (DTNB) has been investigated. Only 0.6 sulfhydryl group of the sulfur-containing enzyme reacts with DTNB. After removal of sulfur from persulfide groups a further 0.6 sulfhydryl group (i.e. a total of 1.2) becomes accessible to the reagent. The resulting enzyme-thionitrobenzoate complex shows an absorption spectrum with a shoulder at 325 nm due to bound thionitrobenzoate. Both thiosulfate and cyanide remove thionitrobenzoate from the enzyme restoring its catalytic properties. The modified enzyme is protected from alkylation by iodoacetate until thionitrobenzoate is removed. The existence of a further sulfhydryl group close to the catalytic one is suggested.

Animals↗
PubMed1976

Reaction of rhodanese with dithiothreitol.

The reaction between bovine rhodanese (thiosulfate:cyanide sulfurtransferase, EC 2.8.1.1) and reduced dithiothreitol has been studied. This reagent, in the absence of thiosulfate, reduces the amount of sulfur carried by rhodanese with formation of sulfide and oxidized dithiothreitol: E-S-SH + reduced dithiothreitol replaced by E-SH + HS- + oxidized dithiothreitol, (E = enzyme). An inactivation was observed at high dithiothreitol/enzyme ratios or at very low enzyme concentrations. The inactivation was not observed in the presence of thiosulfate and can be reversed by cyanide or thiosulfate. A thiosulfate reduction activity of rhodanese was also found using dithiothreitol as reductant.

Animals↗