Figure 3.

Arrhenius plots. The rate of spontaneous production of AP sites and single-strand breaks in DNA exposed to different temperatures in vitro or in vivo. 1, (○), Spontaneous loss of purines from native Bacillus subtilis DNA heated in buffer at pH 5. The low pH experimental values (34) have been recalculated here for conditions of incubation in the same buffer at pH 7.4 based on the published dependence of DNA depurination on pH (34), to permit comparison of rates of spontaneous production of different DNA lesions at physiological pH. 2, (▵), Spontaneous loss of adenine from native calf thymus DNA in 0.005 M phosphate buffer (pH 6.8) (data from refs. 33 and 40). 3, (◊), Spontaneous hydrolysis of the phosphate-diester bond in single-stranded bacterial DNA in 0.0025 M phosphate buffer, pH 6.8 (data from ref. 41). Points a and b, rates of induction by mild hyperthermia of alkali-labile sites, including AP sites, in DNA of human diploid fibroblasts of strains 18J, L3, and D3. The values of the rate constants for strains 18J and L3 were about the same (data from refs. 33 and 26), and, therefore, these values are shown as one point, b. The plotted data were reviewed in ref. 33.