Characterization of the free radical in a plant ribonucleotide reductase

Harder, Jens; Follmann, Hartmut

doi:10.1016/0014-5793(87)80214-4

Cited by 12 publications

(2 citation statements)

References 20 publications

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“…The spectrum of RDPR derived from eukaryotes and certain viruses differs significantly from that of RDPR from E. coli (Sjoberg & Graslund, 1983; Harder & Follmann, 1987). This spectrum can be simulated (Figure 1C) by using a set of hyperfine values (Table I) similar to that described above.…”

Section: Resultsmentioning

confidence: 99%

Protein-tyrosyl radical interactions in photosystem II studied by electron spin resonance and electron nuclear double resonance spectroscopy: comparison with ribonucleotide reductase and in vitro tyrosine

Hoganson

Babcock²

1992

Biochemistry

148

137

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The stable tyrosine radical in photosystem II, YD*, has been studied by ESR and ENDOR spectroscopies to obtain proton hyperfine coupling constants from which the electron spin density distribution can be deduced. Simulations of six previously published ESR spectra of PSII (one at Q band; five at X band, of which two were after specific deuteration and two others were of oriented membranes) can be achieved by using a single set of magnetic parameters that includes anisotropic proton hyperfine tensors, an anisotropic g tensor, and noncoincident axis systems for the g and A tensors. From the spectral simulation of the oriented samples, the orientation of the phenol head group of YD* with respect to the membrane plane has been determined. A similar orientation for YZ*, the redox-active tyrosine in PSII that mediates electron transfer between P680 and the oxygen-evolving complex, is expected. ENDOR spectra of YD* in PSII preparations from spinach and Synechocystis support the set of hyperfine coupling constants but indicate that small differences between the two species exist. Comparison with the results of spectral simulations for tyrosyl radicals in ribonucleotide reductase from prokaryotes or eukaryotes and with in vitro radicals indicates that the spin density distribution remains that of an odd-alternant radical but that interactions with the protein can shift spin density within this basic pattern. The largest changes in spin density occur at the tyrosine phenol oxygen and at the ring carbon para to the oxygen, which indicates that mechanisms exist in the protein environment for fine-tuning the chemical and redox properties of the radical species.

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Section: Resultsmentioning

confidence: 99%

Protein-tyrosyl radical interactions in photosystem II studied by electron spin resonance and electron nuclear double resonance spectroscopy: comparison with ribonucleotide reductase and in vitro tyrosine

Hoganson

Babcock²

1992

Biochemistry

148

137

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“…While the direct reduction of ribonucleotides via a radical mechanism is a general mode of dNPT synthesis in all organisms, the way in which this is achieved varies. At present, three classes of ribonucleotide reductases have been described: The aerobic E. coli enzyme (8) is the prototype for class I enzymes (2'-deoxyribonucleoside-diphosphate:oxidized-thioredoxin 2'-oxidoreductase, EC 1.17.4.1), also present in all higher animal (9) and plant cells (10). These enzymes consist of two proteins: one large homodimer (protein B1 of E. coli) and one small homodimer (protein B2).…”

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confidence: 99%

The anaerobic ribonucleoside triphosphate reductase from Escherichia coli requires S-adenosylmethionine as a cofactor.

Eliasson

Fontecave²,

Jörnvall³

et al. 1990

Proc. Natl. Acad. Sci. U.S.A.

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Extracts from anaerobically grown Escherichia coli contain an oxygen-sensitive activity that reduces CTP to dCTP in the presence of NADPH, dithiothreitol, Mg2e ions, and ATP, different from the aerobic ribonucleoside diphosphate reductase (2'-deoxyribonucleoside-diphosphate: oxidized-thioredoxin 2'-oxidoreductase, EC 1.17.4.1) present in aerobically grown E. coli. After fractionation, the activity required at least five components, two heat-labile protein fractions and several low molecular weight fractions. One protein fraction, suggested to represent the actual ribonucleoside triphosphate reductase was purified extensively and on denaturing gel electrophoresis gave rise to several dermed protein bands, all of which were stained by a polyclonal antibody against one of the two subunits (protein Bi) of the aerobic reductase but not by monoclonal anti-B1 antibodies. Peptide mapping and sequence analyses revealed partly common structures between two types of protein bands but also suggested the presence of an additional component. Obviously, the preparations are heterogeneous and the structure of the reductase is not yet established. The second, crude protein fraction is believed to contain several ancillary enzymes required for the reaction. One of the low molecular weight components is S-adenosylmethionine; a second component is a loosely bound metal. We propose that S-adenosylmethionine together with a metal participates in the generation of the radical required for the reduction of carbon 2' of the ribosyl moiety of CTP.Ribonucleotide reductases catalyze the synthesis of the four deoxyribonucleoside triphosphates (dNTPs) required for DNA replication (1-4). The enzymes provide a link between RNA and DNA metabolism. They have attained special biological interest in connection with recent theories concerning the evolution of life on earth since their appearance was a prerequisite for the transition of an "RNA world" into a "DNA world" (5). Several forms of the enzyme occur in nature, with different structures and catalytic mechanisms. Also, their chemistry is of considerable interest. The enzyme from Escherichia coli provided the first example of a biological process that uses a protein radical as a mechanistic option (6, 7). While the direct reduction of ribonucleotides via a radical mechanism is a general mode of dNPT synthesis in all organisms, the way in which this is achieved varies. At present, three classes of ribonucleotide reductases have been described: The aerobic E. coli enzyme (8) is the prototype for class I enzymes (2'-deoxyribonucleoside-diphosphate:oxidized-thioredoxin 2'-oxidoreductase, EC 1.17.4.1), also present in all higher animal (9) and plant cells (10). These enzymes consist of two proteins: one large homodimer (protein B1 of E. coli) and one small homodimer (protein B2). Characteristic features are the presence of a ferric:tyrosyl radical center in B2 (6) and redox-active dithiols in B1 (11), both involved in the catalytic process. B1 also provides the reductase with allosteric pro...

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Ribonucleoside-diphosphate reductase

Springer Handbook of Enzymes

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Characterization of the free radical in a plant ribonucleotide reductase

Cited by 12 publications

References 20 publications

Protein-tyrosyl radical interactions in photosystem II studied by electron spin resonance and electron nuclear double resonance spectroscopy: comparison with ribonucleotide reductase and in vitro tyrosine

Protein-tyrosyl radical interactions in photosystem II studied by electron spin resonance and electron nuclear double resonance spectroscopy: comparison with ribonucleotide reductase and in vitro tyrosine

The anaerobic ribonucleoside triphosphate reductase from Escherichia coli requires S-adenosylmethionine as a cofactor.

Ribonucleoside-diphosphate reductase

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