Ribonucleotide 2 ,3 -cyclic phosphate

UMP becomes bound to site B which catalyzes the hydrolysis of the phosphomonoester bond. Adenosine and 3 -AMP by binding at site B could interfere with the breakdown of cyclic 2, 3 -UMP. Similarly, binding of bis (p-nitrophenyl) phosphate at site A could interfere with the breakdown of 3 -AMP. Cyclic 2, 3 -UMP and bis(p-nitrophenyl) phosphate compete for site A while adenosine competes with 3 -AMP for site B. Unemoto et al. (7) have examined the mutual inhibition of substrates and substrate analogs for the enzyme from halophilic V. alginolyticus. They also concluded that 3 -ribonucleotides and ribonucleo-side 2, 3 -cyclic phosphates are hydrolyzed at different sites. However, because of the nature of the mutual inhibition between 3 -AMP and bis(p-nitrophenyl) phosphate, they suggested that part of the site for the latter substrate overlaps with the 3 -nucleotidase site. At this time the precise mechanism of action of the enzyme is not settled, but clearly there are two active sites, one a 3 -nucleotidase site and a cyclic phosphate diesterase site. Anraku (18) has described this protein as a double-headed enzyme. 

Sutherland and co-workers have obtained activated pyrimidine ribonucleotides from cyanamide, cyanoacetylene, glycolaldehyde, glyceraldehyde, and inorganic phosphate in a reaction that bypassed free ribose. The synthesis yielded activated ribonucleotide P-ribocytidine-2 ,3 -cyclic phosphate as a major product and several co-products [17]. Prolonged irradiation of this mixture by 254 nm UV-light caused the destruction of various co-products and the partial conversion of P-ribocytidine-2 ,3 -cyclic phosphate into P-ribouridine-2 ,3 -cyclic phosphate. The authors concluded that there must be some (photo)protective mechanism functioning with the two natural nucleotides but not with other pyrimidine nucleosides and nucleotides [17]. 

The ribonucleotide sulfur analogue 2,-deoxy-2,-thiouridine 3 -(/ -nitrophcnyl phosphate) (295) undergoes transphosphorylation to give 2,3 -cyclic phosphorothioate (296) followed by hydrolysis to give 2,-deoxy-2,-thiouridine 2 -phosphorothioate (297)... 

Cyclic ribonucleotides and deoxy-ribonucleotides in biological fluids Spherisorb 10 ODS 0.05 M phosphate buffer (pH 5.6) -same-1-25% methanol and 25% water UV 254 and 280 nm 70... 

Q -D-(5 )i.-/o/ m P-Me, M-178 Methyl 2,3-di-0-methyl-4-thioglucopyranoside 4,6-cyclic phosphonothioate a-D-(5 )p-/orm P-Chloro, M-I79 Methyl 2,3-di-0-methyl-4-thioglucopyranoside 4,6-cyclic phosphonothioate a-D-(P)p-/orm P-Ethoxy, M-179 Methyl 2,3-di-0-methyl-4-thioglucopyranoside 4,6-cyclic phosphonothioate a-D-(5 )p-/o/7n P-Ethoxy, M-179 2-Methyladenosine 5 -Phosphate, M-223 7-Methylguanosine 5 -Phosphate, M-262 Monobutyl 3"-adenylate, A-31 Nicotinamide ribonucleotide, N-45 Nicotinic acid mononucleotide, N-46... 

The amount of nucleosides in cells is negligible also deoxyribonucleotides occur at insignificant levels in tissues. Ribonucleotides are important cellular components and occur as 5 -monophosphates, di-, tri-, and cyclic 3, 5 -phos-phates. Nucleoside phosphates function as energy carriers and serve as precursors for the synthesis of nucleic acids. Cyclic nucleotides (i.e., cyclic 3, 5 -AMP and cyclic-3, 5 -GMP) also play a role in metabolic regulation. 

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