Energy Deposition Events Produced by Fission Neutrons in Aqueous Solutions of Plasmid DNA

By the method of gel electrophoresis, radiation-induced DNA single- and double-strand breaks (SSB, DSB) were studied with a model system of pBR322 solution in vitro in the presence of 'OH radical scavengers, mannitol and TE (10(-2) mol dm(-3) Tris and 10(-3) mol dm(-3) ethylene diamine tetra-acetic acid). Experiments showed that SSB resulted from one-hit events of radiation energy deposition and DSB resulted from both one-hit and two-hit energy deposition events and so were distinguished into two classes of alphaDSB and betaDSB. Moreover, alpha/beta, where alpha is the number of DSB per unit dose induced in one irradiation event and beta the number of DSB per unit squared dose induced by the combination of two independent SSB, was related to the scavenging capacity, sigma, and for sigma > 10(8) s(-1), alphaDSB predominate over DSB. On the other hand, if sigma<2x10(8)s(-1), the measured G(alphaDSB) decreased in parallel with G(SSB), i.e., G(alphaDSB)/G(SSB) was a constant. When sigma>2x10(8) s(-1). G(alphaDSB) decreased slightly so that the ratio of alphaDSB to SSB evidently increased. Therefore, alphaDSB could be induced by the radical transfer mechanism for sigma<2x10(8) s(-1) and contrarily produced by the local multiply damaged sites (LMDS) mechanism for sigma larger than this value. In addition, the distance for two independent complementary SSB forming a DSB was deduced, but no apparent variation of it was found in the wide sigma range from approximately 10(5) to approximately 10(9) s(-)1, which shows that the DNA steric structure was not influenced by mannitol.

Section: Electrophoresismentioning

confidence: 97%

Formation of single- and double-strand breaks of pBR322 plasmid irradiated in the presence of scavengers

Shao¹,

Saito

Zhang³

1999

“…In the experiment conducted under aerobic conditions, the SSB yields caused by γ -rays are predominantly due to OH radicals for scavenging capacities that are cell-like or less than cell-like [38]. The calculated ratio of the OH reaction, 90%, can be explained in terms of the high activity of OH and the oxygen-scavenging effect of H and eaq (Eqs.…”

Section: Comparison With Experimentsmentioning

confidence: 99%

Monte Carlo simulation of DNA strand-break induction in supercoiled plasmid pBR322 DNA from indirect effects

Tomita

Kai

Kusama

et al. 1998

We present a new Monte Carlo simulation code system (DBREAK) of the detailed events that occur when ionizing radiation interacts with water and DNA molecules. The model treats the initial energy deposition by radiation, the formation of chemically active species, subsequent diffusion-controlled chemical reactions, and induction of DNA strand breaks. DBREAK assumes one-hit single-strand break (SSB) and two-hit double-strand break (DSB) mechanisms. A high-resolution model of plasmid DNA structure has been introduced. The calculated results are compared with the results of previously performed experiments of the same type. Under aerobic conditions, 89.4% of the DNA damage was attributed to OH-radical and 10.5% and 0.1% to eaq- and H, respectively. We also compared the differences between liquid-water track structure and gas-phase-water track structure. The calculated yield of SSBs by liquid-water track structure exceeded that of gas-phase-water track structure by a factor of 1.2.

“…The supercoiled form has less ethidium bromide binding ability than the open circular and linear conformations. Therefore, a correction factor of 1.7 for supercoiled pBR322 has been reported to approximate this difference among the three plasmid conformations [15]. The numbers of SSBs and DSBs were calculated by the following equations [16]:…”

Section: Measurements Of Ssb and αDsbmentioning

confidence: 99%

Reaction rate coefficients of hydroxyl radical-induced DNA single- and α-type double-strand breaks

Shao¹,

Zhang²,

Saito

2000

With a model system of pBR322 plasmid DNA solution in vitro, the dose effects of radiation-induced single- and double-strand breaks (SSB and DSB) were measured and DSB was distinguished into alpha- and beta-types. Under the condition of low scavenging capacity existing in the irradiated DNA solution, SSB and alpha DSB were mainly induced by hydroxyl radicals (.OH). Moreover, a certain relationship was obtained between the SSB and alpha DSB yields and the DNA concentration. It was found that when the DNA solution was irradiated in the presence of 2.5 mmol dm-3 mannitol, the reciprocals of G(SSB) and G(alpha DSB), respectively, were linearly related to the reciprocal of the DNA concentration, i.e. the competition reactions of DNA and mannitol for .OH radicals can be described by second-order kinetics. The rate coefficients and the efficiencies of the .OH radical inducing SSB were deduced. Also, the reaction rate coefficients and the efficiencies for the induction of alpha DSB from SSB by the .OH radical transfer mechanism, were first derived from the competition kinetics.