[Effect of inorganic salts on free radicals production by near UV irradiation of frozen aqueous solutions of adenine and its derivatives].

The addition of Na and Ca chlorides to adenine (A), adenosine (Ado) and adenosine diphosphate solutions at pH 5.3 has been shown to result in intensification of EPR signals in samples irradiated by near UV at 77 K and appearance of signals of Cl2-* and peroxyl radicals. The peroxyl radicals contribution can exceed 30% of total amount of paramagnetic products. The addition of inorganic phosphate reduces the contribution of peroxyl radicals. Possible mechanisms of the processes involved are discussed.

[Influence of inorganic phosphate on the production of free radicals in UV-irradiated frozen tyrosine solutions].

The role of inorganic phosphate as a catalyzer of the production of tyrosyl radical in frozen tyrosine solutions irradiated with near UV light at 77K has been demonstrated by the EPR method. It was shown that the increase in the yield of tyrosyl radicals at pH < 7 correlates with the production of H* atoms and can be explained by the fact that phosphate acts as an acceptor of photoejected electrons. At pH > 7, the increase in the yield of tyrosyl radicals is accompanied by the production of phosphate radicals and OH* and is caused, presumably, by the catalysis of the formation of triplet states of tyrosine molecules by the HPO4(2-) form of phosphate, the fact shown by a number of authors. A quantitative estimation of relative concentrations of photosensitized paramagnetic products was carried out on the basis of computer analysis of resultant EPR signals.

[EPR study of the influence of hypoxia on nitric oxide formation in the blood of Krushinskii-Molodkina rats].

The influence of hypoxia on nitric oxide formation in the blood of Krushinskii-Molodkina rats has been studied by electron paramagnetic resonance. It was found that nitric oxide synthesis in Krushinskii-Molodkina rats is increased compared with that in Wistar rats. A significant enhancement of the EPR signal of Hb-NO complexes in the animal blood was observed after hypoxia simulating the altitude of 5000 m above the sea level, in particular in the presence of sodium nitrite and the NO-synthase inhibitor L-nitroarginine. It was assumed that NO synthesis and nitro-/nitrite- reductase systems are activated under hypoxic conditions.

[Effect of irradiation intensity on the production of free radicals by near-UV photosensitization of frozen adenine solutions with an inorganic phosphate].

The effect of light intensity on the production of free radicals by near-UV photosensitization at 77 K of frozen aqueous solutions of adenine in the presence of inorganic phosphate has been studied. A quantitative estimation of relative concentrations of the products: hydrogen atoms (H*), adenine, phosphate and OH* radicals was carried out using the computer analysis of EPR spectra of irradiated samples. It was found that the formation of phosphate and OH* radicals in a photosystem results predominantly from the absorption of two photons in the band of illumination. The production of H* occurs in two ways, which involve the absorption of one photon or two photons.

[Analysis of free-radical products of near-UV irradiation at 77 K of frozen adenine and adenosine diphosphate solutions containing inorganic phosphate].

Irradiation by near-UV light at 77 K of aqueous solutions of inorganic phosphate in weakly acidic conditions in the presence of the photosensitizers adenine and adenosine diphosphate results in the formation of free radicals of these compounds, photosensitized free radicals of phosphate itself, and H* and OH* radicals. The relative concentrations of free radical products were estimated by the analysis of total ESR signals registered in the region of g = 2.00 in the photosystems Ade + Pi and Adphi + Pi using the original computer program of ESR spectra simulation.

[Free radicals photosensitized by near-UV radiation in aqueous adenine solutions in the presence of inorganic phosphate at 77 K].

It was shown that irradiation of aqueous adenine solutions in the presence of inorganic phosphate by near UV at 77 K results in the production of OH* free radicals catalyzed by phosphate and photosensitized formation of phosphate radicals and atoms H*.

[On the nature of free radicals of adenosine diphosphate in redox system NADH-riboflavin-adenosine diphosphate]. / O prirode svobodnykh radikalov adenozindifosfata, obnaruzhivaemykh v redoks-sisteme NADH-riboflavin-adenozindifosfat.

Free radicals formed in redox-system NADH + riboflavin (Rf) containing adenosine diphosphate (ADP) in aqueous solutions at room temperature were investigated by ESR-method. Besides formation during the reaction of semireduced form of ADP heterocycle which is identified by singlet ESR signal arising with halfwidth of about 20 Gs the correlations were shown to appear between intensities of weak low-field and high-field lines, symmetrical relatively field values corresponding to g-factor near 2.00. This was interpreted as the evidence of free radicals formation: PO(3)2-. and free radicals of ADP phosphate fragment.

[Synthesis of ATP and free radicals in an aqueous solution, containing NADH, riboflavin, ADP and inorganic phosphate]. / Sintez ATF i svobodnye radikaly v vodnom rastvore, soderzhashchem NAD.N, riboflavin, ADF i neorganicheskii fosfat.

pH-dependence of initial (admixture) adenosine triphosphate (ATP) changes (ATP synthesis and hydrolysis) was studied for aerated and deaerated aqueous solutions during the incubation of adenosine diphosphate (ADP) and inorganic phosphate (Pi) in the presence of reduced nicotinamide adenine dinucleotide (NADH) and riboflavin (Rf). The preferential pH regions were indicated both for ATP synthesis and ATP hydrolysis (pH less than pH 5.4, 5.9 divided by pH 6.5 and pH greater than 6.6, pH 5.5 divided by pH 5.8 respectively). 'Free radical content measurements were paralleled by ESR technique. On the basis of the obtained results it was assumed that a part of ESP signal attributed to ADP radicals was increased during ATP synthesis.

[Interaction of riboflavin and adenosine diphosphate in an aqueous solution irradiated with visible light]. / Vzaimodeistvie riboflavina i adenozindifosfata v vodnom rastvore pri osveshchenii vidimym svetom.

Interaction of riboflavin (RF) and adenosinediphosphate (ADP) was investigated under conditions of RF photoexcitation. It was shown that in the presence of ADP effective RF triplets quenching and RFH semiquinones formation took place. Subsequent interaction between these RFH and nucleotide resulted in the generation of a semireduced form of ADP.

[Energizing of F1-ATPase after irradiation with visible light]. / Energizatsiia F1-ATFazy pri obluchenii vidimym svetom.

It was shown that ATP synthesis by F1-ATPase sensitized by visible light was combined with oxidation of SH groups and decrease of initial flavin fluorescence in the F1-ATPase preparation. It was suggested that it was an endogenous flavin group that regulated redox transitions between SH-S-S groups which was essential for the catalysis in vivo.

[Electron paramagnetic resonance of the F1-H+-ATPase complex and adenosine triphosphate synthesis after its irradiation with visible light]. / Elektronnyi paramagnitnyi rezonans kompleksa F1-H+-ATPazy i sintez adenozintrifosfata pri ego osveshchenii vidimym svetom.

Under F1-ATPase irradiation by visible light two characteristic features of flavin main activities were detected: I/ESR signal g = 2.00 appearance which was in favor of flavin photochemical electron reduction and 2/photostimulated O2 consumption by F1-ATPase. The dependence of ESR signal g = 2.00 intensity on visible light wavelength completely coincided with the same dependence obtained for proteinless model riboflavin + ADP. Flavin localization in proximity of ADP bound in the enzyme active site was suggested. Under F1-ATPase irradiation by light lambda greater than 350 nm ATP synthesis was obtained similar to the proteinless model riboflavin + ADP + Pinorg. In this model endogenous flavin was suggested to serve as a photosensitizer, its photoexcitement being a model of dark energization of F1-ATPase in oxidative phosphorylation.

[Effect of visible light on the ATP synthetase function of mitochondria]. / Vliianie vidimogo sveta na ATF-sintetaznuiu funktsiiu mitokhondrii.

Dependence of oxidative phosphorylation in rat liver mitochondria on redox state of endogenous flavoenzymes was studied. Regulation of the redox state of endogenous flavins in mitochondria was performed by visible light illumination of lambda = 380 nm in oxygen free as well as in oxygenated media. A decrease of oxidative phosphorylation was obtained at full reduction of flavins (respiratory control and ATP synthesis were measured); this effect was partially recovered when flavin was reoxidized by oxygen. Results of ESR measurements of the signal gl = 2.00 associated with semireduced flavins were in accordance with the appearance of diamagnetically completely reduced form of flavin. These facts may be considered as evidence of the regulative role of flavins in oxidative phosphorylation.

[Adenosine triphosphate synthesis induced by ultraviolet irradiation]. / Sintez adenozintrifosfata, stimulirovannyi ul'trafioletovym oblucheniem.

Effect of UV-irradiation on non-aqueous solutions of adenine nucleotide mixture of the presence of inorganic phosphate was studied. Solutions of ADP sodium salts containing AMP and ATP admixtures and of inorganic phosphate in DMSO and DMPA and ethylene glycol were illuminated with the lamp dPIII-500. It has been shown that along with nucleotide disintegration and complex formation ATP synthesis takes place, which is evidenced by an increase of relative ATP content in experimental specimens.