The reverse of the 'repair' reaction of thiols: H-abstraction at carbon by thiyl radicals.

Thiyl radicals (RS) formed by the reaction of radiolytically generated OH radicals with thiols, e.g. 1,4-dithiothreitol (DTT), react with cis- and trans-2,5-dimethyltetrahydrofuran by abstracting an H atom in the alpha-position to the ether function (k approximately equal to 5 X 10(3) dm3 mol-1 s-1). The so-formed planar ether radical is 'repaired' by the thiol (k = 6 X 10(8) dm3 mol-1 s-1) thereby regenerating a cis- or trans-2,5-dimethyltetrahydrofuran molecule. In this reaction a thiyl radical is reproduced. Thus trans-2,5-Me2THF from cis-2,5-Me2THF and vice versa are formed in a chain reaction: at a dose rate of 2.8 X 10(-3) Gys-1 and a trans-2,5-Me2THF concentration of 1 X 10(-2) mol dm-3 using DTT as the thiol, G(cis-2,5-Me2THF) = 160 has been found. The chain reaction is very sensitive to impurities and also to disulphides such as those radiolytically formed. 2,5-Me2THF can be regarded as a model for the sugar moiety of DNA where the C(4')-radical is known to lead to DNA strand breakage. The possible role of cellular thiols in the repair of the C(4') DNA radical, and also the conceivable role of thiyl radicals inducing DNA strand breakage, are discussed.