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  • Title: 1,N6-ethenoadenine and 3,N4-ethenocytosine are excised by separate human DNA glycosylases.
    Author: Hang B, Chenna A, Rao S, Singer B.
    Journal: Carcinogenesis; 1996 Jan; 17(1):155-7. PubMed ID: 8565126.
    Abstract:
    We previously reported our finding that human cells contain glycosylase activity toward all four etheno bases formed in DNA by chloroacetaldehyde and related bi-functional aldehydes. By enzyme purification, including FPLC, we isolated two separate glycosylase activities for 1,N6-ethenoadenine (epsilon A) and for 3,N4-ethenocytosine (epsilon C) respectively, from crude HeLa cell-free extracts, which also contained a number of well-described glycosylases. When Mono-S FPLC purified proteins were assayed against defined oligomers containing either epsilon A or epsilon C, it was found that epsilon A and epsilon C glycosylases were completely separated. It could also be demonstrated that each enzyme bound to and cut only epsilon A- or epsilon C-containing oligomers respectively. There was no overlap in specificity for these two substrates. Several other human glycosylase substrates were also tested and none were cleaved by epsilon C glycosylase. The epsilon C glycosylase activity identified in the present study apparently represents a previously unknown glycosylase. This work also suggests that enzyme recognition of closely related DNA adducts may depend upon subtle changes in local conformation.
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