Isolation, Identification, and Synthesis of 2-carboxyarabinitol 1-phosphate, a Diurnal Regulator of Ribulose-bisphosphate Carboxylase Activity

The diurnal change in activity of ribulose 1,5-bisphosphate (Rbu-1,5-P(2)) carboxylase [3-phospho-D-glycerate carboxy-lyase (dimerizing); EC 4.1.1.39] of leaves of Phaseolus vulgaris is regulated (in part) by mechanisms that control the level of an endogenous inhibitor that binds tightly to the activated (carbamoylated) form of Rbu-1,5-P(2) carboxylase. This inhibitor was extracted from leaves and copurified with the Rbu-1,5-P(2) carboxylase of the leaves. Further purification by ion-exchange chromatography, adsorption to purified Rbu-1,5-P(2) carboxylase, barium precipitation, and HPLC separation yielded a phosphorylated compound that was a strong inhibitor of Rbu-1,5-P(2) carboxylase. The compound was analyzed by GC/MS, (13)C NMR, and (1)H NMR and shown to be 2-carboxyarabinitol 1-phosphate [(2-C-phosphohydroxymethyl)-D-ribonic acid]. Verification of structure was obtained by comparison of the inhibitory activity of the isolated compound with that of 2-carboxy-D-arabinitol 1-phosphate synthesized in vitro. This compound (but not 2-carboxy-D-arabinitol 5-phosphate) inhibited Rbu-1,5-P(2) carboxylase in a way that was kinetically identical to that of the isolated, naturally occurring compound. The structure of the isolated compound differs from the Rbu-1,5-P(2) carboxylase transition-state analogue 2-carboxyarabinitol 1,5-bisphosphate only by the lack of the C-5 phosphate group. This difference results in a higher binding constant for the monophosphate (K(d) = 32 nM) compared with the bisphosphate (K(d) < 10 pM). The less tightly bound compound acts in a light-dependent, reversible regulation of Rbu-1,5-P(2) carboxylase activity in vivo.