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Title: POTENT INHIBITION OF RIBULOSE-BISPHOSPHATE CARBOXYLASE BY AN OXIDISED IN RIBULOSE-1,5-BISPHOSPHATE

Author
item KANE, HEATHER - AUSTRILIAN NATIONAL UNIV
item WILKIN, JEAN-MARC - AUSTRALIAN NATIONAL UNIV
item PORTIS JR, ARCHIE
item ANDREWS, T - AUSTRALIAN NATIONAL UNIV

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/2/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: The activity of Rubisco, the enzyme that captures carbon dioxide, often limits photosynthesis, the process by which plants use light energy from the sun to make carbohydrates for growth from carbon dioxide and water. One of the substrates of Rubisco is a sugar phosphate, RuBP, which has been known to be unstable for many years and suspected of forming inhibitory breakdown products. Studies of Rubisco have been hindered by a lack of knowledge about this substrate. In this study, we characterize the breakdown of RuBP, identifying the major inhibitory oxidation product and conditions that minimize its formation. This information will benefit scientists attempting to study and modify the properties and regulation of Rubisco in ways beneficial for increased photosynthesis by crop plants.

Technical Abstract: Oxidation of D-ribulose-1,5-bisphosphate (ribulose-P2) during synthesis and/or storage produces D-glycero-1,3-pentodiulose-1,5-bisphosphate (pentodiulose-P2), a potent slow, tight-binding inhibitor of spinach ribulose-P2 carboxylase (Rubisco). Differing degrees of contamination with pentodiulose-P2 cause the decline in Rubisco activity seen during Rubisco assay timecourses to vary between different preparations of ribulose-P2. With some ribulose-P2 preparations, this compound can be the dominant cause of the decline, far exceeding the significance of the catalytic by-product, D-xylulose-1,5-bisphosphate (xylulose-P2). Unlike xylulose-P2, pentodiulose-P2 does not appear to be a significant by-product of catalysis by wildtype Rubisco at saturating CO2 concentration. It is produced slowly during frozen storage of ribulose-P2, even at low pH, more rapidly in Rubisco assay buffers at room temperature, and particularly rapidly on deliberate oxidation of ribulose-P2 with Cu**2+. Its formation can be prevented by exclusion of transition metals and O2. Pentodiulose-P2 is unstable and decays to a variety of other less inhibitory compounds, particularly in the presence of some buffers. However, it forms a tight, stable complex with carbamylated spinach Rubisco that can be isolated by gel filtration, presumably because its structure mimics that of the enediol intermediate of Rubisco catalysis. Rubisco catalyses the cleavage of pentodiulose-P2 by H2O2, producing 2-phosphoglcyolate.