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]
EC Number: 18.104.22.168β-nicotinate D-ribonucleotide + CO2 + diphosphate ← 5-phospho-α-D-ribose 1-diphosphate + quinolinate + 2 H+
The direction shown, i.e. which substrates are on the left and right sides, 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:
pH(opt): 6.5-7.7 [Mann74]
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