Subject(s)
Oxygen , Peroxides , Superoxides , Anions , Chemical Phenomena , Chemistry , Kinetics , Structure-Activity RelationshipABSTRACT
Pulse radiolysis has been used to investigate the rates and transient spectra for the reactions of free radicals with beef heart lactate dehydrogenase at pH 7. Analysis of the results leads to second-order rate-constants for eaq-, .OH, .I, .Br2-, .I2- and .(CNS)2- which are, respectively, 24, 21, 10, 0.55, 0.43 and 0.15 in units of 10(10) M-1 s-1 with uncertainties of +/- 20 per cent. Those for .I and .I2- are similar to the corresponding rate-constants for the related enzyme alcohol dehydrogenase. The spectra of the transient species produced by .OH, .Br2- and .(CNS)2- all showed evidence for reactions with tyrosine and tryptophan residues, and in general terms the magnitudes of the rate-constants appeared to increase with the oxidizing abilities of the radicals. The implication of the results for understanding the mechanism of deactivation by free radicals is discussed.
Subject(s)
L-Lactate Dehydrogenase/analysis , Pulse Radiolysis/methods , Spectrum Analysis/methods , Animals , Cattle , Enzyme Inhibitors/pharmacology , Free Radicals , L-Lactate Dehydrogenase/antagonists & inhibitors , Myocardium/enzymology , Tryptophan/pharmacology , Tyrosine/pharmacologyABSTRACT
The half-wave reduction potentials of a range of nitroheterocyclic compounds were measured polarographically and compared with their radiosensitizing abilities in a simple radiation biochemical assay for damage to 5'-GMP. The chemical enhancement ratio for sensitization of inorganic phosphate release from irradiated 5'-GMP, increased with sensitizer electron affinity, but in a non-linear manner. An onset of sensitization was observed for nitroheterocyclics with half-wave potentials less negative then -0.05V vs. standard calomel electrode and maximum sensitization, approaching the oxygen effect, was obtained at a sensitizer half-wave potential of -0.25 V vs. standard calomel electrode. Nitroheterocyclic sensitizers with half-wave potentials in this range may be potential clinical radiotherapeutic agents.
Subject(s)
Guanine Nucleotides/radiation effects , Polarography/methods , Radiation-Sensitizing Agents , DNA/radiation effects , Electrochemistry , Heterocyclic Compounds , Radiochemistry , Structure-Activity RelationshipABSTRACT
The interaction of ethidium bromide (EB) with DNA has been investigated using the pulse radiolysis technique. In particular, the absolute rate constant for the reaction of hydrated electrons, generated by single pulses of high-energy electrons, with EB is shown to drop dramatically in the presence of DNA. This drop in diffusion-limited reactivity results from the interaction of EB with DNA, effectively immobilising it, thus lowering the reaction cross-section or probability. Analysis of the resulting kinetic spectrophotometric data shows that they are consistent with a reversible interaction of EB with DNA as described by the law of mass action. The Scatchard-type plots obtained are linear, and give quantitative information on the extent and degree of association, comparable with that obtained by more conventional methods. The potential of the pulse radiolysis technique for studying different types of interactions between small molecules and various biopolymers has been demonstrated.
Subject(s)
DNA , Ethidium , Animals , Binding Sites , Cattle , Kinetics , Mathematics , Spectrophotometry/methods , Thymus GlandABSTRACT
Pulse radiolysis has been used to study the interactions of a variety of small molecules with DNA. The diffusion-controlled rate constants for the reactions of e(aq) with dyes, cations and other small molecules including radioprotectors and radiosensitizers, were found to decrease remarkably upon association with DNA. These kinetic data can be used to quantitate the degree and extent of such interactions. This technique may have wide practical application for the in situ study of many small molecule-macromolecule associations, under physiological conditions.
