MetaCyc Enzyme: quinolinate phosphoribosyltransferase (decarboxylating)

Species: Ricinus communis

Subunit composition of quinolinate phosphoribosyltransferase (decarboxylating) = [QPT subunit]2

Quinolinate phosphoribosyltransferase (QPRtase) has been purified from cotyledons of etiolated castor bean (Ricinus communis) seedlings. The enzyme catalyzes the transfer of phosphoribosylpyrophosphate (PRPP) to quinolinate forming the nicotinate mononucleotide under release of CO2 and pyrophosphate. Inhibition experiments with substrate analogues underlined the importance of the 2- and 3-carboxyl group on the pyridine ring for substrate binding. Kinetic studies pointed to the existence of a ternary complex formed by the enzyme and the two substrates PRPP and quinolate [Mann74].

Molecular Weight of Polypeptide: 35 kD (experimental) [Mann74 ]

Molecular Weight of Multimer: 68 kD (experimental) [Mann74]

pI: 6.0 [Mann74]

Gene-Reaction Schematic: ?

Gene-Reaction Schematic

Created 12-Oct-2006 by Foerster H , TAIR

Enzymatic reaction of: quinolinate phosphoribosyltransferase (decarboxylating)

EC Number:

β-nicotinate D-ribonucleotide + CO2 + diphosphate <=> 5-phospho-α-D-ribose 1-diphosphate + quinolinate + 2 H+

The reaction direction shown, that is, A + B ↔ C + D versus C + D ↔ A + B, is in accordance with the Enzyme Commission system.

The reaction is favored in the opposite direction.

In Pathways: NAD biosynthesis I (from aspartate)

Activators (Unknown Mechanism): Mg2+ [Mann74]

Inhibitors (Unknown Mechanism): picolinate [Mann74]

Kinetic Parameters:

Km (μM)
5-phospho-α-D-ribose 1-diphosphate

pH(opt): 6.5-7.7 [Mann74]


Mann74: Mann DF, Byerrum RU (1974). "Quinolinic acid phosphoribosyltransferase from castor bean endosperm. I. Purification and characterization." J Biol Chem 249(21);6817-23. PMID: 4422841

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Please cite the following article in publications resulting from the use of MetaCyc: Caspi et al, Nucleic Acids Research 42:D459-D471 2014
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