D-Ribose 1,5-diphosphate

D-Ribose 1,5-diphosphate (R15P) is a metabolic intermediate and enzyme substrate. Purified Tk-E2b2 converts D-Ribose 1,5-diphosphate into Ribulose-1,5-bisphosphate, with a specific activity of 32.3 μmol min^-1 mg^-1[1][2]. In Vitro:D-Ribose 1,5-diphosphate can be efficiently catalyzed and isomerized to ribulose-1,5-bisphosphate by Tk-R15Pi, with a specific activity of 28.6 ± 1.1 μmol min^-1 mg^-1 and a reaction equilibrium constant of 16.3 ± 0.2. This equilibrium favors product formation^[1].
D-Ribose 1,5-diphosphate is not utilized as a substrate by Tk-R15Pi, as reflected by the undetectable catalytic activity of this anomer (<0.1 μmol min^-1 mg^-1)^[1].
D-Ribose 1,5-diphosphate can be converted into ribulose-1,5-bisphosphate by purified Thermococcus kodakaraensis Tk-E2b2, with a specific activity of 32.3 μmol min^-1 mg^-1[2].