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At normal concentrations, phosphate activates the enzyme by binding to its allosteric regulatory site. However, at high concentrations, phosphate is shown to have an inhibitory effect by competing with the substrate ribose 5-phosphate for binding at the active site. ADP is the key allosteric inhibitor of ribose-phosphate diphosphokinase.
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.
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.
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.
ATP + d-ribose ⇌ ADP + d-ribose 5-phosphate. Thus, the two substrates of this enzyme are ATP and d-ribose, whereas its two products are ADP and d-ribose 5-phosphate. The systematic name of this enzyme class is ATP: d-ribose 5-phosphotransferase. Other names in common use include deoxyribokinase, ribokinase (phosphorylating), and d-ribokinase.
This reaction is catalysed by ribose-phosphate diphosphokinase. [11] Five biosynthetic steps complete the transformation. [1] [12] The first enzyme, amidophosphoribosyltransferase, attaches ammonia from glutamine to the ribotide at its anomeric carbon, forming phosphoribosylamine (PRA): PRPP + glutamine → PRA + glutamate + PPi
In enzymology, a phosphoribokinase (EC 2.7.1.18) is an enzyme that catalyzes the chemical reaction. ATP + D-ribose 5-phosphate ADP + D-ribose 1,5-bisphosphate. Thus, the two substrates of this enzyme are ATP and D-ribose 5-phosphate, whereas its two products are ADP and D-ribose 1,5-bisphosphate.