Interaction of ribulose bisphosphate carboxylase/oxygenase with 2-carboxyhexitol 1,6-bisphosphates

2-C-Carboxy-d-glucitol 1,6-bisphosphate (CGBP) and 2-C-carboxy-D-mannitol 1,6bisphosphate (CMBP) have been synthesized, isolated, and the structures of these compounds and the derived lactones elucidated by NMR spectroscopy and periodate oxidation. Both carboxyhexitol bisphosphates, which are homologs of the transition state analog 2-C-carboxy-d-arabinitol 1,5-bisphosphate, exhibit competitive inhibition of ribulose bisphosphate carboxylase/oxygenase (EC 4.1.1.9) isolated from spinach (Spinacia oleracea), with respect to ribulose 1,5-bisphosphate. CMBP was a more potent inhibitor (100-fold) displaying an inhibition constant (K_i at pH 8.0 and 30 °C) of 1-2 μm with enzymes from spinach, barley (Hordeum vulgare), and Chromatium vinosum. In contrast the Rhodospirillum rubrum enzyme was inhibited about 40-fold more weakly (K_i = 53 μm at pH 8.0 and 30 °C). Both CGBP and CMBP potentiated activation of RuBP carboxylase from spinach and R. rubrum.