期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1983
卷号：80
期号：6
页码：1492-1495
DOI：10.1073/pnas.80.6.1492
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Protein B2, a subunit of ribonucleotide reductase from Escherichia coli, contains in its active form a tyrosyl free radical as part of the polypeptide chain and a dimeric iron center that stabilizes the radical. The enzyme depends on this radical for its catalytic activity. Treatment with hydroxyurea scavenges the radical without disturbing the iron center and, thereby, results in an inactive form of the subunit, B2/HU. A second inactive form, apoB2, lacking both the radical and the iron center, is obtained by treatment of B2 with 8-hydroxyquinoline. Here we describe an enzyme activity in extracts from E. coli that transforms the catalytically inactive B2/HU form into the active B2 subunit by regeneration of the tyrosyl radical. This reaction requires the presence of oxygen, dithiothreitol, and Mg2+ and does not proceed through apoB2. Under anaerobic conditions, we obtained evidence for a second activity in the bacterial extract that destroys the free radical and transforms B2 into B2/HU. We suggest that this novel type of protein modification is functionally related to the synthesis of deoxyribonucleotides and DNA.
