Enzymatic Repair Mechanisms for Base Modifications Induced by Oxygen Radicals

• Published in: JOURNAL OF RADIATION RESEARCH Vol. 38; no. 1; pp. 1 - 4
• Main Authors: Yamamoto, K, Uraki, F, Yonei, S, Yukawa, O
• Format: Journal Article
• Language: English
• Published: England THE JAPAN RADIATION RESEARCH SOCIETY 1997; Oxford University Press
• Subjects: Active oxygen; Amino Acid Sequence; DNA - radiation effects; DNA Damage; DNA Glycosylases; DNA Repair; Enzymes; Escherichia coli - genetics; Escherichia coli - metabolism; Free Radicals - metabolism; Humans; Molecular Sequence Data; N-Glycosyl Hydrolases - genetics; N-Glycosyl Hydrolases - metabolism; Reactive Oxygen Species - metabolism
• ISSN: 0449-3060; 1349-9157
• DOI: 10.1269/jrr.38.1

1. DNA damage produced by oxygen radicals. Oxygen radicals are produced by cellular metabolism, ionizing radiation, and environmental mutagens 1). These radicals react with DNA yielding lesions such as base modifications, strand breaks and crosslinks 2). Of these, base modifications are primary causes of oxygen radical-induced cell lethality, mutagenesis, carcinogenesis, aging and a number of diseases 3). Purine modifications include 4, 6-diamino-5-formamidopyrimidine (Fapy-A), 2, 6-diamino-4-hydroxy-5-formamidopyrimidine (Fapy-G), 8-hydroxyguanine (8ohG) and 8-hydroxyadenine (8ohA). Base pairing between 8ohG and dAMP leads to G：C to T：A transversion mutations 4). Pyrimidine modifications caused by oxygen radicals include thymine glycols, 5-hydroxycytosine and 5-hydroxyuracil. These base modifications and the amounts formed after 420 Gy of γ-rays are shown in Table 1. 2. DNA glycosylases. Enzymatic repair mechanisms have evolved that protect prokaryotes and eukaryotes from the biological consequences of DNA damage produced by oxygen radicals. Escherichia coli possesses several enzymes which are presumed, on the basis of their in vitro specificities, to be involved in the repair of oxygen radical-induced base modifications. Several of these enzymes are induced by damage to DNA 5),6).