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Ribose 5-phosphate (R5P) is both a product and an intermediate of the pentose phosphate pathway. The last step of the oxidative reactions in the pentose phosphate pathway is the production of ribulose 5-phosphate. Depending on the body's state, ribulose 5-phosphate can reversibly isomerize to ribose 5-phosphate.
Ribose-5-phosphate isomerase (Rpi) encoded by the RPIA gene is an enzyme (EC 5.3.1.6) that catalyzes the conversion between ribose-5-phosphate (R5P) and ribulose-5-phosphate (Ru5P). It is a member of a larger class of isomerases which catalyze the interconversion of chemical isomers (in this case structural isomers of pentose ).
Production of ribose 5-phosphate (R5P), used in the synthesis of nucleotides and nucleic acids. Production of erythrose 4-phosphate (E4P) used in the synthesis of aromatic amino acids. Aromatic amino acids, in turn, are precursors for many biosynthetic pathways, including the lignin in wood. [citation needed]
[1] [2] [3] The vitamins thiamine [4] and cobalamin, [5] and the amino acid tryptophan also contain fragments derived from PRPP. [6] It is formed from ribose 5-phosphate (R5P) by the enzyme ribose-phosphate diphosphokinase: [7] It plays a role in transferring phospho-ribose groups in several reactions, some of which are salvage pathways: [8]
A key regulatory step is the production of 5-phospho-α-D-ribosyl 1-pyrophosphate by ribose-phosphate diphosphokinase, which is activated by inorganic phosphate and inactivated by purine ribonucleotides. It is not the committed step to purine synthesis because PRPP is also used in pyrimidine synthesis and salvage pathways.
ADP is the key allosteric inhibitor of ribose-phosphate diphosphokinase. It has been shown that at lower concentrations of the substrate ribose 5-phosphate, ADP may inhibit the enzyme competitively. Ribose-phosphate pyrophosphokinase is also inhibited by some of its downstream biosynthetic products. [2] [6]
The pathway begins with the conversion of Ribose-5-Phosphate(R5P) to phosphoribosyl pyrophosphate (PRPP) by enzyme ribose-phosphate diphosphokinase (PRPS1). PRPP is then converted to 5-phosphoribosylamine (5-PRA) as glutamine donates an amino group to the C-1 of PRPP.
Ribose is a constituent of RNA, and the related molecule, deoxyribose, is a constituent of DNA. Phosphorylated pentoses are important products of the pentose phosphate pathway , most importantly ribose 5-phosphate (R5P), which is used in the synthesis of nucleotides and nucleic acids , and erythrose 4-phosphate (E4P), which is used in the ...
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