Deoxyribose-l-phosphate

A close look at this reaction reveals that in the opposite direction, the reaction is of the phosphorolysis type. For this reason, the enzymes catalyzing the reaction with ribose-l-phosphate are called phosphorylases, and they also participate in nucleic acid degradation pathways. Purine nucleoside phosphorylases thus convert hypoxanthine and guanine to either inosine and guanosine if ribose-l-phosphate is the substrate or to deoxyinosine and deoxyguanosine if deoxyribose-1-phosphate is the substrate. Uridine phosphorylase converts uracil to uridine in the presence of ribose-l-phosphate, and thymidine is formed from thymine and deoxyribose-l-phosphate through the action of thymidine phosphorylase. 

The mechanism of formation of thymine and hydroxymethylcytosine are not yet known, but the addition of a carbon to position 5 appears to involve a transfer from a folic acid derivative. As in the case of the purines, the relation between ribose and deox3nibose nucleotides is obscure. Deoxyribonucleosides can be formed from deoxyribose-l-phosphate by a nucleoside phosphorylase reaction. 

The primary structure of DNA is based on repealing nucleotide units, where each nucleotide is made up of the sugar, i.e., 2 -deoxyribose, a phosphate, and a heterocyclic base, N The most common DNA bases are the purines, adenine (A) and guanine (G), and the pyrimidines, thymine (T) and cytosine (C) (see Fig. I). The base, N, is bound at the l -position of the ribose unit through a heterocyclic nitrogen. 

Milne et al. recently described a new assay for the measurement of TP activity in cell lines and tissues, which is sensitive, automated, and allows the processing of multiple assays simultaneously (15). This method exploits the ability of TP to convert 5-FU to 5-FDUR in the presence of deoxyribose-1-phosphate (dR-l-P). 

Figure 3. Use of 2-deoxyribose-5-phosphate aldolase in the synthesis of fluorinated sugars, (a) Normal reaction, (b) synthesis of l-fluoro-4-hydroxy-5-methyl-hexan-2-one, (c) synthesis of 2,5-dideoxy-5-fluororibose...

S)-[l-2H,3H]ethylene glycol, respectively, to racemic acetaldehyde. Racemic acetaldehyde is also formed in the cleavage of 2-deoxyribose 5-phosphate by a specific aldolase (90), and the incubation of stereospecifically labeled dihy-droxyacetone phosphate with methylglyoxal synthetase gives racemic methyl-glyoxal (pyruvic aldehyde) (91). 

The enzyme purine nucleoside phosphorylase (PNP) catalyses the reversible conversion of both ribo- and 2 -deoxyribo-puranosides to the corresponding free base and ribose or deoxyribose-l-a-phosphate. Its absence is associated with T-cell immunodeficiency and thus inhibitors may be valuable in treating T-cell leukaemia. Of several recently prepared 9-... 

Garcia-Diaz, M., Bebenek, K., Kunkel, T. A., and Blanco, L. (2001). Identification of an intrinsic 5 -deoxyribose-5-phosphate lyase activity in human DNA polymerase lambda. A possible role in base excision repair. J. Biol. Chem. 276, 34659-34663. 

The mode of nthesis of deoxyribose is a subject of active interest at the present time. It has been shown that deoxyribose 5-phosphate can be synthesized by condensation of acetaldehyde and glyceraldehyde 3-phosphate in the presence of an aldolase from animals and bacteria (80). A pathway for deoxyribonucleotides can be formulated which employs this aldolase. The 5-phosphate ester could be converted to a l-phosphate by a mutase, the deoxypentose phosphate condensed with a base to form a nucleoside by nucleoside phosphorylase, and the nucleoside converted to a nucleotide by a kinase [Eq. (26)]. 

C.-H. Wong, E. Garcia-lunceda, L. Chen, O. Blanco, H.I.M. Gijsen, D.H. Steensma, Recombinant 2-deoxyribose-5-phosphate aldolase in organic synthesis use of sequential two-substrate and three-substrate aldol reactions, I. Am. Ghem. Soc. 117 (1995) 3333-3339. 

Gijsen, H. J. M. and Wong, C.-H., Sequential one-pot aldol reactions catalyzed by 2-deoxyribose-5-phosphate aldolase and fructose-l,6-diphosphate aldolase. /. Am. Chem. Soc. 1995,117 (10), 2947-2948. 

DNA is a helical polyanion built by the union of two linear polymeric strands that are composed of sugars (deoxyribose) finked by phosphates. Each sugar contains an aromatic base (G,C,A, or T) bound to C-l of the sugar. The two strands are normally complementary so that when they combine to form the duplex, each base on one strand forms Watson-Crick hydrogen bonds with its counterpart (G with C and A with T) on the opposite... 

The nucleotide sequences of nucleic acids can be represented schematically, as illustrated on the following page by a segment of DNA with five nucleotide units. The phosphate groups are symbolized by (3, and each deoxyribose is symbolized by a vertical line, from C-l at the top to C-5 at the bottom (but keep in mind that... 

The radicals derived from 2-deoxyribose (ribose) upon Oil-attack yield 37% (23%) PNAP-", and it has been concluded that ET only occurs from the C(l ) radicals (Michaels et al. 1976). With CH20H/CH20- the rate of reaction with PNAP is only fast with the anion, CH20 (Adams and Willson 1973). Whether the radicals formed at the other sites in 2-deoxyribose and ribose give (slowly) rise to adducts cannot be deduced from the reported data. Yet, the fact that PNAP enhances the yield of free phosphate in the radiolysis of GMP (Greenstock et al. 1973a) is an indication that such adducts are likely to be formed, but the rate of reaction is very slow with a-phosphatoalkyl radicals (< 5 x 107 dm3 mol 1 s 1 Schuchmann et al. 1995). 

Phosphate Y°> Deoxyribose i l Adenine CD Thymine I 1 Guanine CD Cytosine... 

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