K. V. Shevchenko

New aspects of biosynthesis and metabolism of N-acyldopamines in rat tissues

Possible biosynthetic pathways of N-acyldopamines in rat tissues were compared. It was shown that an insignificant amount of the conjugation products was formed during the incubation of arachidonic acid and dopamine, whereas the substitution of tyrosine for dopamine resulted in the productive biosynthesis of N-arachidonoyldopamine. The biosynthesis presumably involves several closely conjugated enzymatic stages, and free fatty acids rather than their CoA esters served as the starting substrates. The decarboxylation stage probably precedes the stage of catechol system formation, because N-acetyltyramine (a probable intermediate) was easily oxidized by monophenol monooxygenase to N-acyldopamine, whereas N-acyltyrosine is hydrolyzed under these conditions. Biosynthesis of N-acyldopamines in a cell-free medium was accompanied by their methylation. The possibility of oxidative metabolism of N-acyldopamines, which could serve as co-substrates or inhibitors of different oxidoreductases, was shown for the first time.

Efficiency of isotope exchange between sodium 4-phenylbenzoate and activated tritium

The efficiency of the protium–tritium isotope exchange in the sodium 4-phenylbenzoate (PBNa) molecule on activating the reaction on a tungsten filament at 1940 K (target temperature 77 and 295 K) and on heating the substrate supported on 5% Pd/C in the presence of gaseous tritium is compared. It is shown that the reaction mechanism is laregly determined by the properties of the material on which this reaction occurs and not only by the method of generation of activated tritium species. In the reaction of tritium atom with PBNa deposited on glass walls of the reaction vessel, the isotope substitution of tritium for protium occurred by the radical mechanism, leading to the formation of [3H]PBNa and hydrogenation products. It is assumed that the spillover of tritium atom over the support (carbon) surface is accompanied by polarization of the electronic shell and formation of the cluster (3+)(

Specific Features of Deuterium and Tritium Labeling of Pro-Gly-Pro-Leu and of Physiologically Active Amino Acids

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Specific features of deuterium and tritium labeling of SB258585

), which leads to changes in the composition of the reaction products. The combined treatment of PBNa on 5% Pd/C allows estimation of the concentration of clusters on the carbon surface, which reaches 10.9 particles per 100 nm2 (9.2 nm2 per cluster).

Peptide regulation of specific ligand-receptor interactions of GABA with the plasma membranes of nerve cells

The radioactive petide analogue Semax corresponding to the ACTH(4–10) sequence (Met-Glu-His-Phe-Pro-Gly-Pro) with a specific radioactivity of 56 Ci/mmol labeled with tritium at the C-terminal Pro was prepared. The labeled peptide was used for studying the kinetics of Semax penetration into rat brain and blood after its intranasal administration (50 μg/kg, 20 μl of solution) to nonbred white rats of body mass 200–250 g. It was demonstrated that 0.093% of the total introduced radioactivity per gram can be found in the rat brain 2 min after the administration, 80% of this radioactivity belonged to Semax, and the rest, to its metabolites. The peptide undergoes rapid enzymatic degradation, with the tripeptide Pro-Gly-Pro prevailing in biological samples relative to the total content of Semax and its metabolites.

Comparison of pharmacokinetics and metabolism of Pro-Gly-Pro-Leu administered intranasally and intravenously in the blood and brain of rats

Abstractγ-Aminobutyric acid (GABA), 3-hydroxy-L-tyrosine (D0PA), and Pro-Gly-Pro-Leu were labeled with hydrogen isotopes. The mean deuterium content per molecule was 7.5 atoms in Pro-Gly-Pro-Leu and up to 4 atoms in GABA and DOPA. The incorporation of isotopes depending on the reaction conditions was monitored by mass spectrometry. The isotope exchange efficiency was found to strongly depend not only on the reaction temperature and catalyst: substrate ratio, but also on processes occurring on the support surface.

Characteristic features of specific binding of pentapeptide HFPGP labeled at the C-terminal proline residue to rat forebrain plasma membranes.

It has been shown that when a mixture of sodium 4-phenylbenzoate and 5% Pd/C preliminarily exposed to a molecular tritium atmosphere at 333 K for 25 min is treated with atomic protium, tritium is incorporated into sodium 4-phenylbenzoate molecules. The resulting molar radioactivity of this compound is as high as 0.8 ± 0.2 Ci/mmol, and the molar radioactivity of 4-cyclohexylbenzoic acid turns out to be fourto-five times higher than that of labeled sodium 4-phenylbenzoate. It has been suggested that the interaction of protium atoms with (3H+)(ē) clusters formed on the support surface upon tritium spillover can initiate isotope exchange and hydrogenation reactions.

Studies of peculiarities of binding of the Semax neuropeptide, with a labeled terminal proline residue to plasma membranes of rat brain

Samples of SB258 585 labeled with hydrogen isotopes were synthesized. [2H]SB258 585 containing one 2H atom per molecule and [3H]SB258585 with the molar radioactivity of 15 Ci mmol−1 were obtained in preparative amounts. From 0.18 to 1.5 2H atoms were incorporated, on the average, into an SB 258 585 molecule depending on the reaction conditions. The isotope exchange efficiency strongly depends not only on the catalyst-substrate ratio and on the reaction temperature, but also on processes occurring on the support surface. The isotope effects strongly influence the degree of deuterium or tritium incorporation into the samples in cases when the organic compound largely decomposes in the course of the reaction.