Oxidative stress as a cause for ageing

Angelo Schouten d_quale at dds.nl
Tue Sep 26 13:04:24 EST 1995


In article <Pine.SCO.3.91.950921134107.29268A-100000-100000-100000-100000 at skull.cc.fc.ul.pt>,
   Jorge Braz <qjpcbraz at cc.fc.ul.pt> wrote:
>	I am looking for any information about the reactions of oxygen 
>radicals (o2.-, HO., O1, H2O2) with the DNA bases especially the rate 
>constants and the products percentages of this reactions.
>			 Jorge Braz

This is a job for a physical chemist, Jorge. Perhaps theoretical calulations 
have been done. It is of no use to look for rate constant(s) of hydroxyl radicals
with DNA bases in certain media. (.OH) is so extremely reactive and anti-specific/selective 
that it virtually does not excist. It even reacts with inert gases like Xenon.
Therefor the toxicity of H2O2 in Fenton RedOx coupled reactions is related to 
the ease at which .OH (or superoxide, depending on the reaction conditions)
is "released". That is the rate determining step. 
H2O2 should have little genotoxicity "an sich" -as a pure substance.

You could consider to do time resolved pulsed EPR (Spin ECHO experiments).  
All of the intermediates .OH and (O2)- and singlet/triplet O
have unpaired electron spins. Inducing the radical species (photolytic: UV) and watch the 
EPR signals become silent/silenced. Calibrate with a known spin marker like DPPH or TEMPO(L).
Continuous Wave EPR is probably to slow to detect/determine .OH species.
The solvent is important as well. Excited dioxygen species like singlet oxygen live longer in 
apolar and aprotic media than i.g. in water. You only need 10E-12 spins to get an EPR signal.

Best regards,

Angelo Schouten




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