Oxygen Effect and Chemical Repair

The OER is expressed by the Alper formula (81), where m is the maximum response at very high [02] and K is the [02] when the response is half of its maximum value (Alper 1979). 

The concept is based on a very simplified scheme [reactions (82)-(86)]. 

The importance of reaction (84) in this scheme has been pointed out (Schulte-Frohlinde and Bothe 1990), and on the model level, transforming DNA (Held et al. 1981) or SSB formation (Prakash Rao et al. 1992), a chemical repair by RSH beyond OH-scavenging [reaction (85)] has been clearly shown. 

However, this simplified scheme does not account for the fact that in many cases the oxygen effect is biphasic or even more complex (e.g Ewing and Powersl976, 1980 Millar et al. 1979 Tallentire et al. 1972), and the mathematics of such a complex situation has been discussed (Millar and Scott 1981 Alper 1983,1984 Koch 1985 Scott 1986). An example of such a multiphasic OER is shown in Fig. 12.16. 

The time scale of the oxygen effect is of particular interest as it yields information as to the lifetime of the free-radical lesions in a cellular environment. Several approaches to measure such lifetimes have been followed (Adams et al. 1976b Michael 1984 Adams 1985). 

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