Nucleotides reductases

The most conspicuous use of iron in biological systems is in our blood, where the erythrocytes are filled with the oxygen-binding protein hemoglobin. The red color of blood is due to the iron atom bound to the heme group in hemoglobin. Similar heme-bound iron atoms are present in a number of proteins involved in electron-transfer reactions, notably cytochromes. A chemically more sophisticated use of iron is found in an enzyme, ribo nucleotide reductase, that catalyzes the conversion of ribonucleotides to deoxyribonucleotides, an important step in the synthesis of the building blocks of DNA. 

The phosphoribosyltiansferases The nucleoside kinases Nucleoside phosphokinases Nucleotide reductases Methylases and demethylases Other anabolic enzymes Catabolism... 

During the past 15 years data from experiments with different types of animal tissues and micro-organisms, using intact cells, crude extracts or purified enzymes, have firmly established the general occurrence of nucleotide reductases and have stressed their importance for DNA synthesis in essentially all types of rapidly growing cells [54]. It has been proposed that ribonucleotide diphosphates lose a hydroxide ion from C-2 to form a carbonium ion which is then stero-specifically reduced by a hydride ion derived from thioredoxin [54]. Adenosine diphosphate and guanosine diphosphate (as well as uridine and cytidine diphosphates) are reduced in this manner. 

Isolation of "Photosynthetic Pyridine Nucleotide Reductase (PPNR) from spinach chloroplasts... 

Isolation of "Triphosphopyridine Nucleotide Reductase from a photosynthetic bacterium... 

Crystallization of Clostridium pasteurianum ferredoxin demonstration of functional interchangeability of spinach photosynthetic pyridine nucleotide reductase and bacterial ferredoxin suggestion that both be classified as ferredoxins... 

In 1956, San Pietro and Lang (87) found that the soluble fraction from chloroplasts was necessary for the photoreduction of DPN when a small amount of chloroplasts was used. Two years later, San Pietro and Lang (88) reported the purification of a factor from the soluble fraction, which they described as an enzyme named photosynthetic pyridine nucleotide reductase (PPNR). In earlier experiments, the preferred acceptor was DPN (San Pietro and Lang (87) but with the partially purified enzyme the rate of DPN reduction was 70 percent that observed with TPN (San Pietro and Lang (88)). 

Apella, E., and A. San Pietro Physical properties of photosynthetic pyridine nucleotide reductase. Biochem. Biophys. Res. Commun. 6, 349—358 (1962). 

Photosynthetic pyridine nucleotide reductase. IV. Further studies on the chemical properties of the protein. In Photosynthesis Mechanisms in Green Plants, Publ. 1145, Nat. Acad. Sci.-Nat. Res. Council (U. S.), pp. 252—26 (1963). 

Photosynthetic pyridine nucleotide reductase. I. Partial purification and... 

Shapiro, D. M. The purification and properties of photosynthetic pyridine nucleotide reductase from Euglena gracilis. Doctoral Thesis, Johns Hopkins University, Baltimore, Md. Quoted by San Pietro and Black (1965) (1961). 

R. A. Alberty, Thermodynamic properties of nucleotide reductase reactions. Biochemistry, 43,9840-9845 (2004). 

These nucleotide analogues have been evaluated for inhibition of the nucleotide reductase enzymes but exhibited no activity. ... 

Spectroscopic studies indicate homolytic cleavage of the enzyme bound coenzyme to a deoxyadenosyl radical (ACH2 ) and Bi2r as a common characteristic of these enzymatic reactions. Isomerization, described above, involves an apparent intramolecular 1,2-shift of a hydrogen and an electronegative group (X = OH, NH2, Table 1, entry 4 to 6) or a carbon skeleton (Table 1, entry 7 to 10). However, in the nucleotide reductase system, coenzyme B12 has a unique role of radical initiator in a radical chain mechanism rather... 

This parasite also differs from T. foetus in that it lacks nucleotide reductase activity. Pyrimidine deoxynucleotides are obtained by salvage of deoxynucleosides by the deoxyribonucleoside phosphotransferase which acts not only on pyrimidine but also purine deoxyribonucleosides (22). 

San Pietro A, Lang HM Photosynthetic pyridine nucleotide reductase. 1. Partial purification and properties of the enzyme from spinach. J Biol Chem 1958, 231(l) 211-229. 

Reducing equivalents from a ven thioredoxin can be donated to a variety of reductase enzymes. They are not specific for the nucleotide reductase or for enzymes from the same organism. Reduced yeast thioredoxin will serve as reductant for methionine sulphoxide reductase, sulphate reductase and the E. coli nucleoside diphosphate reductase. Heat-stable protein cofactors are known to be involved in each of these systems. 

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