Fig. 5.

Isotopic species of ribulose 1,5-bisphosphate (RuBP) after incomplete reaction run (5% reaction) in D₂O as a solvent with ordinary RuBP (deuterium at natural abundance) as a substrate and Rubisco from tobacco. Assays were carried out with CO₂ (carboxylase, blue) or O₂ (oxygenase, red) at the concentration (in µM) shown on x axes. A control with no reaction (NR) is also shown. Isotopic species were monitored using accurate mass high resolution LC-MS analysis. Protiated [i.e., nondeuterated (A), monodeuterated (B), and dideuterated (C)] RuBP in % of total nonconsumed RuBP. (D and E) Proportions of deuterium at the two sites of exchange (presumably, C3 and O3) calculated from B and C. (F) Relationship between % D at the two sites. Letters stand for statistical classes (P < 0.05, ANOVA). Other nondeuterated isotopic species that did not vary or were negligible (¹⁸O, ¹³C, and ¹³C₂) are not shown. ND, value hardly visible on this graph (0.004%).