A study on comparative molecular properties of Trypanosoma (Nannomonas) Congolense.

Abstract

he many diverse and phenotypically unrelated diseases that occur with high frequency in aging mammalian species may have only a few primary causes. There is ample experimental evidence indicating that some of the essential and beneficial cellular metabolic reactions spontaneously generate free radicals and other highly reactive agents which may diffuse from their place of origin throughout the cell and damage some of its components. Free radicals have been implicated by radiobiological data as one of the mechanisms by which the radiation damage to cellular components is effected. The cellular genome has been shown to be a very important target of free radical damage to cells. The effect of the free radicals would not be different whether the free radicals are spontaneously generated or are caused by radiation. The occurrence in the cell of free radical-dependent reactions and the potential damage these radicals can cause has led to the proposition that protein-DNA cross-links may be spontaneously caused as side effects of the essential cellular metabolic processes. Since protein-DNA cross-links as caused by irradiation of cells is very poorly reparable, it is proposed further that the naturally caused protein-DNA cross-links accumulate with age in mammalian species and that these cross-links may be an important primary cause of aging in mammals. The possible natural occurrence and accumulation of protein-DNA cross-links in mouse liver tissue was investigated as the problem of this thesis using several methods: the SDS-KC1, chloroform and nitrocellulose filter assays to detect protein-DNA complexes and the differential centrifugation and exclusion chromatography assays to determine extractability of chromosomal proteins. Results of the SDS-KCl and chloroform methods imply that protein-DNA cross-links occur in mouse liver chromatin and that chromatin prepared from old mice have more abundant protein-DNA cross-links than that prepared from young mice. This indication is further supported by results obtained using the more sensitive nitrocellulose membrane filter assay for protein-DNA cross-links. Data from the salt extractability assay also support the conclusion of a higher bonding stability of chromosomal proteins obtained from older animals. Collectively, these data strongly suggest that protein-DNA cross-link formation is one of the important processes that occur with age in mammalian chromatin. These results support our working hypothesis that protein-DNA cross-links may be an important primary aging process in mammalian species.