[The effect of benz(a)pyrene on the thermal characteristics of DNA in vivo and in vitro].

Thermal properties of DNA-benz(a)pyrene complex and chromatin within liver cells in BALB/c mice and Macaca fascicularis monkeys after benz(a)pyrene administration were studied using a highly sensitive differential scanning microcalorimeter designed for investigations of dilute biopolymer solutions and complex biological systems. It was shown that benz(a)pyrene (BP) had different efforts on DNA in vivo and in vitro. It was established that at a molar ratio r < 0.03 BP/DNA bp, benz(a)pyrene served as a stabilizing but at higher concentrations as a destabilizing factor of DNA. It was found that BP damaged liver DNA stronger than bone marrow and spleen DNA of a given animal in vivo. Based on analysis of heat redistribution at the heat absorption stages corresponding to denaturation of inactive and active chromatin, we concluded that BP is capable of causing specific breaks in the DNA chain of inactive chromatin and unfolding the whole domain-loop of chromatin, which should lead to uncontrolled genome activation and, therefore, to carcinogenesis.