The inhibition of ribulose 1,5-bisphosphate carboxylase oxygenase by several 2-carboxyhexitol 1- and 6-phosphates

Conversion of D-hamamelose into 2-carboxy-D-arabinitol and 2-carboxy-D-arabinitol 1-phosphate in leaves of Phaseolus vulgaris L

[1-14C]Hamamelose (2-hydroxymethyl-D-ribose) was synthesized by reaction of ribulose 5-phosphate with potassium [14C]cyanide, catalytic hydrogenation of the resulting cyanohydrin, and dephosphorylation of the product. Its identity was established by a chromatographic comparison with hamamelose isolated from the bark of witch hazel (Hamamelis virginiana L.). Following vacuum infiltration of the [1-14C]hamamelose into leaf discs from Phaseolus vulgaris L., 14C-labeled 2carboxy-D-arabinitol (CA) and 2-carboxy-D-arabinitol 1-phosphate (CA1P) were formed, in the dark. Conversion of hamamelose to both CA and CA1P in the leaf discs was inhibited by dithiothreitol and sodium fluoride, although at high concentrations of these inhibitors conversion into CA was still evident when conversion into CA1P was totally inhibited. Wheat (Triticum aestivum L.) leaves converted hamamelose into CA without formation of CA1P. Leaves from P. vulgaris contained 68 nmol.g-1 fresh weight of hamamelose in the light and 35 nmol.g-1 fresh weight in the dark. A pathway for the biosynthesis of CA1P from Calvin cycle intermediates is proposed which includes the sequence: hamamelose --> CA --> CA1P.

Ribulose 1,5-bisphosphate carboxylase-oxygenase. I. Structural, immunochemical and catalytic properties

Some structural, immunochemical and catalytic properties are examined for ribulose 1,5-bisphosphate carboxylase-oxygenase from various cellular organisms including bacteria, cyanobacteria, algae and higher plants. The native enzyme molecular masses and the subunit polypeptide compositions vary according to enzyme sources. The molecular masses of the large and small subunits from different cellular organisms, on the other hand, show a relatively high homology due to their well-conserved primary amino acid sequence, especially that of the large subunit. In higher plants, the native enzyme and the large subunit are recognized by the antibodies raised against either the native or large subunit, whereas the small subunit apparently cross-reacts only with the antibodies directed against itself. A wide diversity exists, however, in the serological response of the native enzyme and its subunits with antibodies directed against the native enzyme or its subunits from different cellular organisms. According to numerous kinetic studies, the carboxylase and oxygenase reactions of the enzyme with ribulose 1,5-bisphosphate and carbon dioxide or oxygen require activation by carbon dioxide and magnesium prior to catalysis with ribulose 1,5-bisphosphate and carbon dioxide or oxygen. The activation and catalysis are also under the regulation of other metal ions and a number of chloroplastic metabolites. Recent double-labeling experiments using radioactive ribulose 1,5-bisphosphate and 14CO2 have elucidated the carboxylase/oxygenase ratios of the enzymes from different organisms. Another approach, i.e., genetic experiments, has also been used to examine the modification of the carboxylase/oxygenase ratio.