A-D-Ribose-1-phosphate

The enzyme [EC 2.4.2.1], also known as inosine phos-phorylase, catalyzes the reaction of a purine nucleoside with orthophosphate to produce a purine and a-D-ribose 1-phosphate. The enzyme will also catalyze the activity of nucleoside ribosyltransferase. 

A fast micromcthod (10-15 nmol scale) for the identification of glycosyl phosphate anomers based on spectrophotometric measurement of the rate of dieir acid-catalysed hydrolysis has been described. The standard Gibbs free-energy change for hydrolysis of a-D-ribose 1-phosphate has been determined. 

This enzyme [EC 2.4.2.10], also known as orotidyhc acid phosphorylase and orotidine-5 -phosphate pyrophosph-orylase, catalyzes the reaction of orotate with 5-phospho-a-D-ribose 1-diphosphate to produce orotidine 5 -phos-phate and pyrophosphate (or, diphosphate). 

This enzyme [EC 5.4.2.7], also known as phosphodeoxy-ribomutase, catalyzes the interconversion of D-ribose 1-phosphate and D-ribose 5-phosphate. This enzyme will also catalyze the interconversion of 2-deoxy-D-ribose 1-phosphate and 2-deoxy-D-ribose 5-phosphate. The bisphosphate compound is the cofactor thus, D-ribose 1,5-bisphosphate, 2-deoxy-D-ribose 1,5-bisphosphate, or even a-D-glucose 1,6-bisphosphate. 

Some phosphoric acid derivatives of 2-desoxy-D-ribose have been obtained by enzymic methods of preparation. A reaction analogous to the phosphorolysis of glycogen to D-glucose 1-phosphate241 has been effected with either hypoxanthine- or guanine-D-riboside, both of which could be split by enzymic phosphorolysis with the formation of D-ribose 1-phosphate.242 The successful conclusion of these experiments prompted similar investigations with desoxyribonucleosides. 

Manson and Lampen243 reported that they obtained the phosphorolysis and arsenolysis of hypoxanthine desoxyriboside by enzyme preparations from calf-thymus gland and rat liver. An acid-stable phosphate ester was isolated as a product of phosphorolysis. Results to be outlined suggested that this ester was 2-desoxy-D-ribose 5-phosphate and evidence was obtained for its formation by a mutase type reaction from 2-desoxy-D-ribose 1-phosphate. This evidence was extended and reinforced when Manson and Lampen244 obtained indications for the formation of desoxy-D-ribose 1-phosphate during the phosphorolysis of thymidine. Consequently the conversions outlined may be depicted as shown. 

Kalckar117118119 has shown that the enzymatic phosphorolysis of inosine (hypoxanthine 9-D-ribofuranoside) may give rise to the formation of a pentose phosphate, isolable as its barium salt. The phosphate was found to be non-reducing although easily hydrolyzed by either acid or alkali to equimolar quantities of phosphate and pentose. In view of these properties and the fact that it could be used for the enzymatic synthesis of purine ribosides, Kalckar has tentatively assigned to it the D-ribose 1-phosphate structure its ring structure and configuration at carbon 1 remain undetermined. 

Scheme 14.13. A representation of a salvage reaction in which a purine (adenine, A) undergoes reaction with a-D-ribose-l-phosphate in what is represented as an SN2-type process but which almost certainly involves participation by the ring oxygen as well as purine nucleoside phosphorylase (EC 2.4.2.1). NB The name of the enzyme as a phosphorylase refers to its potential to catalyze the reverse of the reaction shown.

The TK-catalyzed reaction requires the presence of thiamine pyrophosphate and Mg " as cofactors. Although the substrate specificity of the enzyme has not been thoroughly investigated, it has been shown that the enzyme accepts a wide variety of 2-hydroxyaldehydes including D-glyceraldehyde 3-phosphate [591-57-1], D-glyceraldehyde [453-17-8], D-ribose 5-phosphate /47(9(9-2%/7, D-erythrose 4-phosphate and D-erythrose [583-50-6] (139,149—151). 

The 2-deoxy-D-ribose 5-phosphate aldolase (RibA or DERA EC 4.1.2.4) is a class I enzyme that in vivo catalyzes the reversible addition of ethanal to D-glyceraldehyde... 

Phosphoglucomutase acts not only on D-glucose and D-mannose phosphates (see p. 204) but also on D-ribose phosphates, the interconversion of D-ribosyl phosphate and D-ribose 5-phosphate being similarly accelerated by D-glucose 1,6-diphosphate,193 which appears to generate D-ribose 1,5-diphos-phate as cofactor.199(a) (b) (o) D-Ribose 5-phosphate is formed from D-ribose and ATP in the presence of yeast ribokinase.m... 

This thiamin pyrophosphate-dependent enzyme [EC 2.2.1.1], also known as glycolaldehyde transferase, catalyzes the reversible reaction of sedoheptulose 7-phos-phate with D-glyceraldehyde 3-phosphate to produce D-ribose 5-phosphate and o-xylulose 5-phosphate. The enzyme exhibits a wide specificity for both reactants. It also can catalyze the reaction of hydroxypyruvate with R—CHO to produce carbon dioxide and R—CH(OH)—C(=0)—CH2OH. Transketolase isolated from Alkaligenes faecalis shows high activity with D-erythrose as the acceptor substrate. 

Functionally and mechanistically reminiscent of the pyruvate lyases, the 2-deoxy-D-ribose 5-phosphate (121) aldolase (RibA EC 4.1.2.4) [363] is involved in the deoxynucleotide metabolism where it catalyzes the addition of acetaldehyde (122) to D-glyceraldehyde 3-phosphate (12) via the transient formation of a lysine Schiff base intermediate (class I). Hence, it is a unique aldolase in that it uses two aldehydic substrates both as the aldol donor and acceptor components. RibA enzymes from several microbial and animal sources have been purified [363-365], and those from Lactobacillus plantarum and E. coli could be induced to crystallization [365-367]. In addition, the E. coli RibA has been cloned [368] and overexpressed. It has a usefully high specific activity [369] of 58 Umg-1 and high affinity for acetaldehyde as the natural aldol donor component (Km = 1.7 mM) [370]. The equilibrium constant for the formation of 121 of 2 x 10M does not strongly favor synthesis. Interestingly, the enzyme s relaxed acceptor specificity allows for substitution of both cosubstrates propional-dehyde 111, acetone 123, or fluoroacetone 124 can replace 122 as the donor [370,371], and a number of aldehydes up to a chain length of 4 non-hydrogen atoms are tolerated as the acceptor moiety (Table 6). 

For preparative applications, the expensive and configurationally unstable donor 128 can be simply prepared in situ by the action of ribose 5-phosphate isomerase (EC 5.3.1.6) on D-ribose 5-phosphate (39). This technique was applied to the stereoselective synthesis of d-[1-13C] fructose 6-phosphate 38 from [13C] formaldehyde [376,377] which also included a second enzymatic isomerization of the D-arafrino-3-hexulose 6-phosphate intermediate 129 into the more stable 2-hexulose derivative 38. Notable are the conflicting demands for high substrate levels (necessary to shift the fully reversible multi-component equilibrium) versus the notorious enzyme inactivation that occurs at higher formaldehyde concentrations. 

D-Ribose 5-phosphate D-glycero-D-altro-octulox 1,8-bisphosphate 3 61" A 33 TPI 170 33... 

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