[The mechanism of in vivo arylamine acetyltransferase activation]. / Mekhanizm aktivatsii in vivo arilamin-atsetiltransferazy.

A kinetic analysis of arylamine acetyltransferase activation by prodigiozane, a stimulator of organism unspecific resistance, has been carried out. The change of enzyme activity is associated not with a change of its tissue content, but is due to the appearance of a new isoenzyme with altered rate of product dissociation from the catalytic site under condition when k-1 much greater than kKaT. The effect observed is suggested to be defined by a genetically determined adaptative mobility of organism rather than by genetically determined enzyme synthesis. A search strategy for arylamine acetyltransferase activity regulators is proposed.

[Interaction of ubisemiquinone with succinate dehydrogenase and the cytochrome chain of mitochondria]. / Vzaimodeistvie ubisemikhinona s suktsinatdegidrogenazoi i tsitokhromnoi tsep'iu mitokhondrii.

The free radical EPR signals of ubisemiquinone in mitochondria and submitochondrial particles (SMP) were investigated. One of the signals observed under the conditions of the respiratory chain highly oxidized and characterized by an unusually short time of the spin-lattice relaxation has previously been termed as SQ-2. The intensity of SQ-2 in SMP strongly depends on pH, the maximal concentration of QH. is reached at about 8.5. The signal is absent in the succinate dehydrogenase-depleted SMP and is highly sensitive to specific inhibitors of succinate: CoQ-oxidoreductase, such as alpha-thenoyltrifluoroacetone and carboxin. In SMP SQ-2 disappears in the presence of low concentrations of ferricyanide, while in mitochondria this non-penetrating oxidant provokes the appearance of SQ-2. The data obtained suggest that SQ-2 belongs to a stable ubisemiquinone which forms a complex with a FeS center of succinate dehydrogenase, is localized at the M-side of the membrane, and is kinetically isolated from the cytochrome chain. Oxidation of the terminal segment of the respiratory chain of mitochondria and SMP reduced by succinate in the presence of antimycin, is in some cases accompanied by an appearance of a strong free radical EPR signal which is stable at 77K but disappears rapidly in the frozen samples at -30- -40 degrees C. It is suggested that the signal is generated by an antimycin-insensitive oxidation of QH2 to QH. via the branch of the respiratory chain comprised of the Rieske FeS-protein and cytochrome c1. The mechanisms of how the two-electron oxidation-reduction of CoQ is coupled with the one-electron transfer through the cytochromes and FeS centers in the respiratory chain are discussed.

[Inhibition of H2O2 and O2-. generation in the respiratory chain, treated with 2,3-dimercaptopropanol]. / Podavlenie generatsii H2O2 i O2- . v dykhatel) noi tsepi, obrabotannoi 2,3-dimerkaptopropanolom.

Inhibition of electron transport in bovine heart submitochondrial particles resulting from treatment with British antilewisite is accompanied by suppression of superoxide radical and H2O2 generation at the b-c1 site of the respiratory chain. In conjunction with the previously obtained data, the results suggest that the effect of British antilewisite is directed towards the step of ubihydroqinone oxidation to ubisemiquinone by the Rieske FeS-protein.

[Tiron as a spin-trap for superoxide radicals produced by the respiratory chain of submitochondrial particles]. / Tairon kak spinovaia lovushka dlia superoksidnykh radikalov, obrazuemykh dykhatel'noi tsep'iu sybmitokhondrial'nykh chastits.

Tiron can be used as a spin-trap for O2 radicals generated by the respiratory chain of submitochondrial particles (SMP). Using this sensitive method, it was shown that the O2 (radical) production by the succinate-oxidizing SMP can be reduced by antimycin or 4-nonyl-2-hydroxyquinoline-N-oxide, the effects of both antibiotics being abolished and prevented by cyanide. It is suggested tht the O2 radicals are produced due to autooxidation of ubisemiquinone which is formed as an intermediate upon one-electron oxidation of CoQH2 by cytochrome c1. The effects of antimycin, 2-nonyl-4-hydroxyquinoline-N-oxide and cyanide on the O2 (radical) generation correlate with the effects of these inhibitors on a steady-state concentration of ubisemiquinone predicted by the Mitchell's Q-cycle hypothesis.

[Interaction of ubisemiquinone with the high-potential iron-sulfur center of submitochondrial particle succinate dehydrogenase. EPR study at 240 and 12 degrees K]. / Vzaimodeistvie ubisemikhinoma s vysokopotentsial'nym zhelezo-sernym tsentrom suktsinatdegidrogenazy submitokhondrial'nykh chastits. EPR-issledovanie pri 240 i 12 gradusa K.

The ESR spectra of beef heart submitochondrial particles were measured in the same samples at 240 degrees and 12 degrees K. There is close similarity between the inhibitory action of alpha-thenoyltrifluoroacetone, ethanol and ferricyanide on the non-saturating free radical signal SQ-2 observed at 240 degree K and peak at g=1.99 (and 2.04) which is visible only at very low temperatures. This result strongly supports our previous proposal that both ESR signals are manifestations of the ubisemiquinone complex with the High-Potential Iron-Sulfur protein of succinate dehydrogenase.