Advances in genetics. Volume 10 / edited by E.W. Caspari and J.M. Thoday.

Date:
1961
Catalogue details

Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Advances in genetics. Volume 10 / edited by E.W. Caspari and J.M. Thoday. Source: Wellcome Collection.

    18/448 (page 4)
    4 в. А. KIHLMAN Alper and Howard-Flanders (1956) found that the sensitivity of microorganisms to X-rays at different oxygen concentrations could be fitted by the equation: S_ ^ m[02] + К Ss [O2] + К where S is the sensitivity at the oxygen concentration [O2] and >Sn the sensitivity in the absence of oxygen. The factor m represents the maxi¬ mum enhancement ratio, or the ratio between a given dose and that dose which in oxygen produces the same effect as the given dose in the absence of oxygen. К is that oxygen concentration in [xM which gives 400r AT 50r/MlN. Û 10 20 30 40 50 60 70 80 90 100 (AIR) PeRCENTAGE OF OXYGEN IN EXPOSURE CHAMBER (NORMAL ATMOSPHERIC PRESSURE) Fig. 1. Relation between percentage of oxygen and yield of X-ray-induced chromosome interchanges in Tradescantia microspores. (From Giles and Beatty, 1950.) a sensitivity of {m1)/2 times the radiosensitivity in nitrogen. When m — d, as is usually the case when X-rays are used, the sensitivity is increased by the oxygen concentration К to a level halfway between the maximum sensitivity and the nitrogen sensitivity. In the experiments of Howard-Flanders and Alper (1957), an m-value of 2.92 and a X-value of 4.0 ±: 0.4 ¡xM were obtained for the bacterium Shigella fiexneri. Values of the same order of magnitude were obtained by Howard-Flanders and Alper in experiments with hap¬ loid yeast, Saccharomyces cerevisiae. The К value for Shigella fiexneri has subsequently been corrected by Howard-Flanders to 1 ¡xM, however (Howard-Flanders, 1958; Howard-Flanders and Jockey, 1960). In a study of the influence of oxygen concentration on the frequencies of X-ray-induced abnormal anaphases in mouse ascites tumors, Desch-