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Biomedical subjects

G Czapski

Publications and source records attributed to G Czapski.

At least 19 recordsLinked to original sources
PubMed1995

The reaction of NO. with O2.- and HO2.: a pulse radiolysis study.

The reactions of NO. with O2.- and with HO2. were studied using the pulse radiolysis technique under pseudo first order conditions where ([O2.-]o + [HO2.]o) > [NO.]o at pH 3.3-10.0. The rate constant of the reaction of NO. with O2.- was determined both by monitoring the decay of O2.- at 250 nm and the formation of ONOO- at 302 nm to be (4.3 +/- 0.5) x 10(9) M-1s-1, independent of ionic strength and pH in the range of 6.1-10.0. The rate constant of the reaction of NO. with HO2.- was determined by following the decay of HO2. at 250 nm to be (3.2 +/- 0.3) x 10(9) M-1s-1 at pH 3.3.

Free Radicals↗
PubMed1995

The role of the reactions of .NO with superoxide and oxygen in biological systems: a kinetic approach.

In this study we calculate the half-life of .NO in its reactions with superoxide and with oxygen under various conditions using the known rate constants for these reactions. The measured half-life of .NO in biological systems is 3-5 s, which agrees well with the calculated value for intracellular .NO, but not for extracellular .NO under normal physiological conditions. The autoxidation of .NO to yield NO2- as a final product cannot be responsible for such a short measured half-life under normal as well as pathologic conditions. Therefore, if there is direct evidence for the occurrence of the reaction of .NO with O2.- in the medium, one has to assume that the steady state concentrations of free .NO are much lower than those measured. The very low concentrations of free .NO in biological systems may result from its reversible strong binding to biological molecules. Simulation of the mechanism of the autoxidation of .NO indicates that the binding constants of .NO to O2 or to another .NO are too small to account for the very low concentration of free .NO in biological systems. Nevertheless, the reaction of .NO with oxygen cannot be neglected in biological systems if the intermediate ONOO. reacts rapidly with a biological target. The biological damage caused by ONOO. is expected to be due to the radical itself and to peroxynitrite, which is most probably formed via the reaction of ONOO. with the biological molecule.

Free Radicals↗
PubMed1994

Free radicals induced peptide damage in the presence of transition metal ions: a plausible pathway for biological deleterious processes.

When aqueous N2O-saturated solutions containing glycine-N-tert-butylamide (L) and Cr2+ (aq) or Cu+ (aq) are irradiated, transients with metal-carbon sigma-bonds are formed with rate constants of (4.4 +/- 0.5) x 10(7) and (5.2 +/- 0.3) x 10(9) M-1 s-1, respectively. In the chromium(II) system, after a fast process (k = 43 +/- 4 s-1), possibly chelation, the transient decomposes very slowly (k = 0.003 +/- 0.001 h-1) via a beta-elimination process to yield 2-methylpropene and glycinamide, i.e., a cleavage of the peptide bond takes place. However, in the copper(I) system the heterolytic cleavage of the sigma-bond and the reaction of the transient complex with L-Cu2+ compete efficiently with the beta-elimination process. The latter reaction leads to some modification of the amide. We suggest that the formation and decomposition of transients with metal-carbon sigma-bonds may describe an additional pathway for peptide damage induced by aliphatic free radical precursors (e.g., OH., H2O2) in the presence of transition metal ions.

Chromium↗
PubMed1993

The Fenton reagents.

Numerous transition metal ions and their complexes in their lower oxidation states (LmMn+) were found to have the oxidative features of the Fenton reagent, and, therefore, the mixtures of these metal compounds with H2O2 were named "Fenton-like" reagents. Using the Marcus theory and the experimental data in the literature, it is shown that in most cases the reaction of these metal complexes with H2O2 is unlikely to occur via an outer-sphere electron-transfer mechanism. It is suggested that the first step in this process is the formation of a transient complex LmM-H2O2n+, which may decompose to an .OH radical or a higher oxidation state of the metal, LmM(n + 2)+, or it may yield an organic free radical in the presence of organic substrates. Thus, the question whether free .OH radicals are being formed or not via the Fenton reaction depends on the relative rates of the decomposition reactions of the metal-peroxide complex and that of its reaction with organic substrates. Contradictory conclusions described from the study of different systems might only indicate that these relative rates are different in these systems.

Hydrogen Peroxide↗
PubMed1993

On the cytotoxicity of irradiated media. To what extent are stable products of radial chain reactions in physiological saline responsible for cell death?

In a previous publication (Czapski et al. 1992) we reported that HOCl accounts for the toxicity of irradiated phosphate-buffered saline towards Escherichia coli bacterial cells. We have now investigated the respective toxicities towards lambda phage and mammalian cells. For phage, as with bacteria, cytotoxicity of the irradiated media seems to derive from HOCl without detectable contribution of H2O2. Mammalian cells (V79 CHO), in contrast, are more sensitive to H2O2 than to HOCl. Both agents, however, are not able to account quantitatively for the toxicity of irradiated solutions towards V79 cells; a hitherto unidentified chlorine/oxygen derivative--being formed in the sub-micromolar concentration range--is suggested to be responsible for toxicity in the case of eukaryotes.

Animals↗
PubMed1992

Radiation-induced generation of chlorine derivatives in N2O-saturated phosphate buffered saline: toxic effects on Escherichia coli cells.

The radiolysis of aqueous chloride solutions has been investigated using pulse and steady-state methods. We have found a correlation between the yields of Cl2- and HOCl formed in pulse-irradiated N2O-saturated solutions. The yields increased with the increasing concentrations of Cl- and phosphate. Phosphate enhanced the yield of Cl2- in neutral solutions because of a proton transfer from H2PO4- to HOCl- with a rate constant of (2.6 +/- 0.5) x 10(8) M-1s-1. HOCl could not be detected in pulse-irradiated He or air-saturated, phosphate-buffered saline (PBS) solutions or in gamma-irradiated N2O, He, or air-saturated PBS solutions. The results are discussed in light of previously suggested mechanisms for the formation and decay of Cl2-. Pulse-irradiated N2O-saturated PBS solutions have a lethal effect on Escherichia coli cells, which is proportional to the amount of HOCl in the solutions. Gamma-irradiation of cells in N2O-saturated PBS solution also raises the radiosensitivity of the cells, although HOCl does not accumulate in this system. The effects of the radiation-induced toxic products on E. coli cells are similar to the effects of NaOCl. The cell membrane is probably the site of physiological injury induced by the radiation products.

Adenosine Triphosphate↗
PubMed1991

Comparison between different assays for superoxide dismutase-like activity.

The direct and indirect methods for assaying the superoxide dismutase activity of a compound are compared. With the use of a direct method, the mechanism of the catalysis of O2- dismutation by the tested compound can be determined, while with the indirect method it cannot, and this may lead to misinterpretation of the results. Assuming that the catalysis occurs via the 'ping-pong' mechanism, both the direct and indirect methods are limited to the determination of values of kcat greater than 10(5) M-1 s-1 and kcat greater than 3 x 10(6) M-1 s-1, respectively. Moreover, many side reactions may occur with the indirect method which may interfere with the measurements. Nevertheless, the indirect method approximates better the in vivo conditions than the direct method, and a tested compound that has high SOD activity using a direct method and low SOD activity using an indirect method, will most probably be a poor SOD mimic in vivo.

Catalysis↗
PubMed1991

The relative efficiency of radicals in radiation damage to deoxyribose.

The radiation damage to Deoxyribose was studied with a view to identify the damaging species. Our results indicate that H, eaq-, CO2- do not cause any appreciable damage in the absence of metal compounds and .OH is the sole damaging entity. Iron compounds sensitize very little O2- damage and CO2- damage could not be sensitized. In N2-saturated solutions metal compounds increase the damage by converting eaq- into deleterious .OH.

Copper↗
PubMed1991

Requirements for SOD mimics operating in vitro to work also in vivo.

When an efficient SOD mimic operating in vitro is introduced into cells, the following requirements are needed in order that this compound will catalyze O2- dismutation efficiently: it should be non toxic, stable, has a long metabolic half life, does not form ternary complexes with the cell components, its reduced form reacts slowly with molecular oxygen, should be able to cross cell membranes and also to reach lipophilic or hydrophobic regions. Thus, it seems that finding an efficient compound that has high SOD-like activity in vivo will not be easily achieved.

Catalysis↗
PubMed1991

SOD-like activity studies of cytokinin-copper(II) complexes.

Using the pulse radiolysis technique it was shown that copper(II) complexes of kinetin and 6-benzylaminopurine (6-BAP) catalyze O2- dismutation very efficiently at physiological pH. The 'turnover' rate constants at pH 7 were determined to be (1.5 +/- 0.3) x 10(9) and (2.2 +/- 0.4) x 10(9) M-1s-1 for 6-BAP and kinetin, respectively. The system was studied at pH 3-10 in the case of 6-BAP, and the results show that this complex catalyzes also HO2 dismutation efficiently.

Adenine↗
PubMed1991

Determination of the superoxide dismutase-like activity of cimetidine-Cu(II) complexes.

Using the direct method of pulse radiolysis to determine the superoxide dismutase like activity of copper(II) cimetidine complexes, it was found that the reaction rate constant with O2-, kcat, was (8.5 +/- 0.5) x 10(8) M-1s-1 independent of the cimetidine concentrations present in excess of 50-200 microM over the metal. The results suggest that either the 1:1 ligand to metal complex does not catalyze O2- dismutation at a comparable rate to that of the 2:1 complex, or that the stability constant of the last species is much higher than that determined earlier by Kimura et al., and only the 2:1 species is present in the solutions. With the indirect methods of cytochrome c and NBT for determining the ability of these complexes to catalyze O2 dismutation, these compounds exhibited a much lower SOD activity, and kcat was determined to be (5.0 +/- 0.3) x 10(6) and (7.6 +/- 0.4) x 10(7) M-1s-1, respectively using the two assays.

Cimetidine↗
PubMed1991

An expanded function for superoxide dismutase.

alpha-Hydroxyalkylperoxyl radicals were generated from the primary and secondary alcohols methanol, ethanol and 2-propanol in N2O/O2-saturated aqueous solutions by pulse radiolysis. These radicals reduced a ferric iron porphyrin complex, tetrakis-(4-N-methylpyridyl)porphine, with diffusion-controlled rate constants. The extreme sensitivity of the shift of the Soret absorption band in this reaction was used to determine, by competition kinetics, the reactivity of the peroxyl radicals with different proteins. Only native Cu,Zn-superoxide dismutase and metallothionein showed competitive behavior, with SOD exhibiting rate constants close to the dismutation rate for O2-. Metallothionein was slower by a factor of 30 with hydroxymethylperoxyl radicals. We propose, that SOD has unique properties of the protein surface in addition to the prosthetic copper site, having possibly evolved as a 'general-purpose radical-scavenging protein'.

Alcohols↗
PubMed1991

Bactericidal activity of catecholamine copper complexes.

Washed or growing E. coli cells are killed by epinephrine, norepinephrine or dopamine in the presence of non lethal concentrations of Cu(II). Killing is enhanced by anoxia and by sublethal concentrations of H2O2. The rate of killing is proportional to the rate of catecholamine oxidation. The copper epinephrine complex binds to E. coli cells, induces membrane damage and depletion of the cellular ATP pool. The cells may be partially protected by SOD or catalase but not by OH radical scavengers. Addition of H2O2 to cells which were sensitized by preincubation with the epinephrine-copper complex, causes rapid killing and DNA degradation. Sensitized cells are not protected by BSA.

Adenosine Triphosphate↗
PubMed1991

Hydrogen peroxide dependent oxidative degradation of DNA by copper epinephrine.

The hydrogen peroxide dependent oxidation of the epinephrine-copper complex to adrenochrome is mediated by free copper ions. The oxidation is enhanced by chloride ions and by the presence of serum albumin. The reaction is not inhibited by SOD or by hydroxyl radical scavengers. The 2:1 epinephrine or dopamine:Cu(II) complexes are able to bind to DNA and to catalyze its oxidative destruction in the presence of hydrogen peroxide. The DNA-epinephrine-Cu(II) terenary complex has characteristic spectral properties. It has the capacity to catalyze the reduction of oxygen or H2O2 and it preserves the capacity over a wide range of complex:DNA ratios. The rate of DNA clevage is proportional to the rate of epinephrine oxidation and the rate determining step of the reaction seems to be the reduction of free Cu(II) ions. The ability to form redox active stable DNA ternary complexes, suggests that under specific physiological conditions, when "free" copper ions are available, catecholamines may induce oxidative degradation of DNA and other biological macromolecules.

Copper↗
PubMed1990

Enhancement of the rate of the beta-elimination of phosphate from radicals derived from glycerol-2-phosphate by Cu(I)-phenanthroline. A pulse radiolysis study.

Hydroxyl radicals abstract hydrogen atoms from glycerol-2-phosphate with a specific rate constant of (7.0 +/- 1.5) x 10(8) M-1s-1 forming the beta-phospho radical as the major product. At physiological pH this radical undergoes a beta-phosphate elimination with a rate constant less than or equal to 1 x 10(3) s-1. The beta-phospho radical reacts with Cu(I)-phenanthroline to produce an unstable transient with a metal-carbon sigma-bond which has an absorbance similar to that of the cuprous phenanthroline complex in the visible region. This intermediate decomposes via a beta-elimination of phosphate with a rate constant of (1.0 +/- 1.5) x 10(4) s-1, which was independent of the acidity in the pH range 4-9.

DNA Damage↗
PubMed1990

A reinvestigation of the reaction of desferrioxamine with superoxide radicals. A pulse radiolysis study.

The reaction of desferrioxamine with superoxide has been studied using the pulse radiolysis technique. The decay of O2- was not accelerated in the presence of up to 4 x 10(-4) M desferrioxamine at physiological pH. The rate constant was found to be lower than 2 x 10(4) M-1s-1. In acid solutions the rate constant of the reaction between desferrioxamine and HO'2 was found to be lower than 10(5) M-1s-1. The reaction was not studied in alkaline solutions due to the high absorbance of desferrioxamine in the U.V. region. The pK of desferrioxamine was determined to be 9.2 +/- 0.05.

Deferoxamine↗