Biomedical subjects

F Thomé

Publications and source records attributed to F Thomé.

6 recordsLinked to original sources

PubMed1992

[Deglutition syncope].

In cases with a history of swallow syncope, an ECG should immediately be taken during ingestion of solid or liquid food in order to determine the rhythm disturbances responsible for the syncopes. Both esophageal passage and cardiac diagnosis are indicated, since, as shown in the literature, pathologic findings are not uncommon. The triad syncope, bradyarrhythmia while swallowing is considered to be an indication for definitive electrostimulation (pacemaker implantation) unless, exceptionally, halting digitalis medication puts an end to the syncopes.

Aged↗

PubMed1989

A new type of chemically modified tRNA as a tool for the study of tRNA-aminoacyl-tRNA synthetase interaction.

tRNA(Phe) in which the adenine and cytosine rings in the aminoacyl arm and in the anticodon loop were converted to alkylating derivatives by mild treatment with methyl chlorotetrolate was used to study the tRNA(Phe)-yeast phenylalanyl-tRNA(Phe) synthetase interaction. At neutral pH, modified tRNA inhibited the enzyme competitively. At pH 9 this binding is accompanied by irreversible inactivation of the enzyme due to alkylation of the alpha subunit of the synthetase. Such a derivatization of tRNA could probably be used to investigate the interaction of other tRNAs with their cognate synthetases.

Alkylation↗

PubMed1988

Reaction of nucleic acid bases with alpha-acetylenic esters. Part IV. Preparation of an alkylating derivative of tRNA(Phe) by conformation-specific chemical modification.

The reaction of yeast tRNA(Phe) with methyl chlorotetrolate, ClCH2-C identical to C-COOCH3, was studied. This reagent converts adenine and cytosine rings into derivatives in which an additional heterocycle bearing the alkylating chloromethyl group is fused to the original base; these derivatives can exist in two isomeric forms. Modified nucleosides of this type can be easily identified by reverse-phase HPLC. It was found that under native conditions, the modification of tRNA involves the anticodon loop and the 3'-end. The isomers of adenine derivatives formed in the anticodon loop were different from those formed in the 3'-end. It is suggested that the isomeric structure of the derivatives is related to the fine conformational differences between these two regions of tRNA(Phe). Methyl chlorotetrolate could thus be used as a conformational probe of single-stranded nucleic acids. Preliminary assays showed that modified tRNA(Phe) binds irreversibly to yeast phenylalanyl-tRNA synthetase.

Alkylation↗

PubMed1987

Reactions of nucleic acid bases with alpha-acetylenic esters. Synthesis and enzymatic evaluation of chemically modified nucleotides.

Analogues of adenine nucleotides, containing an additional chloromethyl-pyrimidone ring fused to the purine base, were obtained by treatment of AMP, ADP and ATP with an alpha-acetylenic ester, methyl 4-chlorobut-2-ynoate. These compounds were tested for their ability to substitute for the natural substrates or cofactors of several enzymes. With the ADP analogue, pyruvate kinase showed a significant increase of the Km value and a moderate decrease of V, while the reverse was observed when hexokinase was tested with modified ATP. Adenylate kinase was active with the ATP analogue but not with the AMP derivative. Myosin accepted the ATP analogue as a substrate, but was irreversibly modified. Among the dehydrogenases tested, only glucose-6-phosphate dehydrogenase was inhibited by the nucleotide analogue. The structure--activity relationship of these nucleotide derivatives, which represent the largest dimensional deviation known from natural nucleotides, is discussed in comparison with some earlier described dimensional probes of enzyme-nucleotide binding sites.

Adenine Nucleotides↗

PubMed1985

Bromopyruvate, a potential affinity label for octopine dehydrogenase.

Bromopyruvate, an analogue of pyruvate, one of the substrates of octopine dehydrogenase, was tested as an inhibitor of the enzyme. Provided both the coenzyme and the second substrate, arginine, were present, bromopyruvate rapidly inactivated the enzyme. This inactivation was irreversible, obeyed pseudo-first order kinetics and exhibited a rate saturation effect. Pyruvate protected the enzyme against inactivation by bromopyruvate and these compounds competed for the same site. Bromopyruvate also behaved as a true substrate for the enzyme. This reagent thus exhibits the kinetic characteristics of a good affinity label for octopine dehydrogenase.

Affinity Labels↗

PubMed1977

Human platelet actin. Evidence of beta and gamma forms and similarity of properties with sarcomeric actin.

Human blood platelet actin was purified using 30% sucrose to extract actomyosin and potassium iodide to dissociate actomyosin and to depolymerize actin. Pure actin thus obtained resembles skeletic muscle actin in its polymerization properties, CD spectra and ability to activate myosin myosin Mg2+-ATPase. Isoelectric focusing gel analysis shows that human blood platelet actin exists in beta and gamma forms. The ratio of beta to gamma forms is of 5 in purified actin, in whole cell extract and in all the fractions studied.

Actins↗