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：1999
卷号：96
期号：22
页码：12339-12344
DOI：10.1073/pnas.96.22.12339
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Ribonucleotide reductases (RNRs) catalyze the conversion of nucleotides to deoxynucleotides. Class I RNRs are composed of two types of subunits: RNR1 contains the active site for reduction and the binding sites for the nucleotide allosteric effectors. RNR2 contains the diiron-tyrosyl radical (Y*) cofactor essential for the reduction process. Studies in yeast have recently identified four RNR subunits: Y1 and Y3, Y2 and Y4. These proteins have been expressed in Saccharomyces cerevisiae and in Escherichia coli and purified to {approx}90% homogeneity. The specific activity of Y1 isolated from yeast and E. coli is 0.03 {micro}mol*min-1*mg-1 and of (His)6-Y2 [(His)6-Y2-K387N] from yeast is 0.037 {micro}mol*min-1*mg-1 (0.125 {micro}mol*min-1*mg-1). Y2, Y3, and Y4 isolated from E. coli have no measurable activity. Efforts to generate Y* in Y2 or Y4 using Fe2+, O2, and reductant have been unsuccessful. However, preliminary studies show that incubation of Y4 and Fe2+ with inactive E. coli Y2 followed by addition of O2 generates Y2 with a specific activity of 0.069 {micro}mol*min-1*mg-1 and a Y*. A similar experiment with (His)6-Y2-K387N, Y4, O2, and Fe2+ results in an increase in its specific activity to 0.30 {micro}mol*min-1*mg-1. Studies with antibodies to Y4 and Y2 reveal that they can form a complex in vivo. Y4 appears to play an important role in diiron-Y* assembly of Y2.
