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Biomedical subjects

G Czapski

Publications and source records attributed to G Czapski.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1988

A critical reevaluation of some assay methods for superoxide dismutase activity.

We have compared the direct method of pulse radiolysis to the indirect methods of cytochrome c and nitroblue tetrazolium for assaying the superoxide dismutase activity of a compound. We have shown that with pulse radiolysis, where high concentrations of O2- are generated, the "turnover" rate constant, kcat, can be determined directly, while with the indirect methods, where relatively low steady state concentrations of O2- are formed, the value of kcat determined by these methods, can be orders of magnitude lower than that determined directly. The main reason for the lower values obtained with the indirect methods is due to the fast reoxidation of the reduced compound by molecular oxygen. Additional problems which arise with the use of indirect methods for determining superoxide dismutase catalytic activity are discussed.

Copper↗
PubMed1988

What is unique about superoxide toxicity as compared to other biological reductants? A hypothesis.

Usually the toxicity of superoxide is attributed to its ability to reduce metal ions and subsequently reoxidation of the metal by hydrogen peroxide yields deleterious oxidizing species. As many other nontoxic biological reductants reduce metal compounds, we suggest that part of the mechanism of superoxide toxicity results from its ability to oxidize metal ions bound to biological targets, which subsequently degrade the target via an intramolecular electron transfer reaction.

Cations↗
PubMed1987

Mechanism of reduction of bleomycin-Cu(II) by CO2- and oxidation of bleomycin-Cu(I) by H2O2 in the absence and presence of DNA.

The reduction reaction of bleomycin-Cu(II) by CO2- has been studied by gamma and pulse radiolysis at pH7. The CO2- radical reduces bleomycin-Cu(II) at a rate of (6.7 +/- 0.7) X 10(8) dm3 mol-1 s-1. In the presence of calf thymus DNA the rate of the reduction decreased as the concentration of DNA increased, indicating that the reduction reaction proceeds through free bleomycin-Cu(II). The stoichiometry and the kinetics of the oxidation of bleomycin-Cu(I) by H2O2 in the presence and absence of DNA have been studied. Our observations suggest that the OH. radical is not produced during this reaction and the degradation of the drug occurs in the absence and presence of DNA. We assume that bleomycin-Cu(II) in the presence of a reducing agent and molecular oxygen or H2O2 does not cleave DNA since the oxidizing species, which are formed during the oxidation reaction by H2O2, attack the drug even in the presence of DNA.

Bleomycin↗
PubMed1987

Ascorbic acid oxidation and DNA scission catalyzed by iron and copper chelates.

The asorbic acid (AH-) auto-oxidation rates catalyzed by copper chelates of 1,10-phenanthroline (OP) or by iron chelates of bleomycin (BLM) are only slightly higher than the oxidation rates catalyzed by the metal ions. AH- oxidation in the presence of DNA is accompanied by degradation of the DNA. The rates of DNA scission by the metal chelates are markedly higher than the rates induced by the free metal ions. AH- oxidation is slowed down in the presence of DNA which forms ternary complexes with the chelates. The ternary complexes react slowly with AH- but induce DNA double strand breaks more efficiently than the free metal chelates. With OP, DNA is degraded by the reaction of the ternary complex, DNA-(OP)2Cu(I), with H2O2. AH- oxidation in the presence of DNA was biphasic, showing a marked rate increase after DNA was cleaved. We suggest that this sigmoidal pattern of the oxidation curves reflects the low initial oxidative activity of the ternary complexes, accelerating as DNA is degraded. Using O2- produced by pulse radiolysis as a reductant, we found that AH- oxidation with (OP)2Cu(II) induced more DNA double strand breaks per single strand break than bipyridine-copper. The site specific DNA damaging reactions indicated by these results are relevant to the mechanism of cytotoxic activities of bleomycin and similar antibiotics or cytotoxic agents.

Ascorbic Acid↗