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|Title:||Mechanisms and Intermediates of Iron Bleomycin Catalyzed Oxidations|
|Department / Program:||Biochemistry|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Health Sciences, Pharmacology
|Abstract:||Based on analogy to other known molecular dioxygen activating metallo-systems, it is presumed that iron bleomycin generates a reactive oxygen intermediate by the reductive cleavage of the dioxygen O-O bond. The molecular details of this activation and the exact chemical nature of the resulting intermediate has remained largely undefined. The ability of ferric bleomycin to use hydroperoxy compounds and mediate the oxidation of small organic substrates in vitro has been utilized in the design of mechanistic studies which probe the chemical mechanisms and reactive intermediates involved in iron bleomycin catalyzed oxidations.
The bleomycin catalyzed N-demethylation of N,N-dimethylaniline yielded equivalent intra- and inter-substrate deuterium isotope effects when activated with either ferrous ion and dioxygen or ferric ion and H$\sb2$O$\sb2$, primary or tertiary alkyl hydroperoxides. The addition of a series of free radical scavengers and inhibitors failed to significantly inhibit the reaction. These results suggest a mechanistic homology between the dioxygen and hydroperoxide dependent pathways and that the oxidative reactivity is not mediated via dissociable free radical species.
Quantitative evaluation of the bleomycin catalyzed reduction products from cumene hydroperoxide, 2-phenyl-2-butyl hydroperoxide, phenylperoxyacetic acid, and 10-hydroperoxy-8,12-octadecadienoic acid revealed products indicative of homolytic peroxy O-O bond cleavage over a variety of reaction conditions. In the case of 10-hydroperoxy-8,12-octadecadienoic acid, the homolytic products were generated exclusively, while supporting the drug dependent oxidation of phenol or the degradation of DNA.
The presence of a homolytic O-O cleavage mechanism was further substantiated by the EPR detection and identification of oxygen free radical species in incubations of ferric bleomycin and tertiary-alkyl hydroperoxides.
A survey of oxidative reactions typically catalyzed by various heme proteins found the reactivities demonstrated by ferric bleomycin to share many interesting overlaps with both the peroxidases and the cytochromes P-450. Included in this survey were heteroatom dealkylation, peroxidation reactions, aromatic and alkyl hydroxylation, hydroperoxide and peroxyacid decomposition, and peroxidative chlorination.
Collectively, these results suggest that ferric bleomycin mediates the homolytic scission of peroxy O-O bonds generating transient oxygen free radical species in close proximity to the metal center which are capable of oxidizing a variety of organic substrates in a manner similar to the various heme proteins. By extension then, a similar mechanism may be operative in the ferrous bleomycin-dioxygen activation pathway.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.
|Date Available in IDEALS:||2014-12-15|