Читать книгу Plant Nucleotide Metabolism - Hiroshi Ashihara - Страница 44

Reduction of the ribose moiety of the ribonucleotide occurs at the ribonucleoside diphosphate level by ribonucleotide reductase (EC 1.17.4.1). The reaction is:

dNDP is phosphorylated to dNTP and used for replication and repair in DNA biosynthesis. It has been shown that ribonucleotide reductase, comprising two large (R1) and two small (R2) subunits, catalyses a rate-limiting step in the production of deoxyribonucleotides required for DNA synthesis. The large subunit (R1) contains the allosteric regulatory sites, while the small subunit (R2) encompasses a binuclear iron centre and a tyrosyl free radical (Elledge et al. 1992). In mammals, defective ribonucleotide reductase often leads to cell cycle arrest, growth retardation, and apoptosis, whereas abnormally increased levels result in higher mutation rates. Similar phenomena have been demonstrated in mutants of A. thaliana. The results suggest that ribonucleotide reductases are critical for cell cycle progression, DNA damage repair, and general development in plants (Wang and Liu 2006). The pathway for thymidine nucleotides, which are required for DNA synthesis, is described in Chapter 10