Metals and other ligands balance carbon fixation and photorespiration in chloroplasts

The behavior of many plant enzymes depends on the metals and other ligands to which they are bound. A previous study demonstrated that tobacco Rubisco binds almost equally to magnesium and manganese and rapidly exchanges one metal for the other. The present study characterizes the kinetics of Rubisco and the plastidial malic enzyme when bound to either metal. When Rubisco purified from five C3 species was bound to magnesium rather than manganese, the specificity for CO2 over O2, (Sc/o) increased by 25% and the ratio of the maximum velocities of carboxylation / oxygenation (Vcmax/Vomax) increased by 39%. For the recombinant plastidial malic enzyme, the forward reaction (malate decarboxylation) was 30% slower and the reverse reaction (pyruvate carboxylation) was three times faster when bound to manganese rather than magnesium. Adding 6-phosphoglycerate and NADP+ inhibited carboxylation and oxygenation when Rubisco was bound to magnesium and stimulated oxygenation when it was bound to mang..., Carboxylation/2PGA measurements: We added an assay buffer containing 20 mM Tris–HCl, 1 mM EDTA, 100 mM Triethanolamine at pH 7.8 to one 5 mL tube; added 1 or 2 μL of Rubisco (0.5–1 μM), 10 μL of 250 mM NaHCO3, 0.5 μL carbonic anhydrase (~2.5 units), 5 μL of iPGM (10 μM), 4 μL of MgCl2 (final concentration 20 mM) or MnCl2 (5 mM); mixed everything thoroughly and allowed the mixture to sit for 5 minutes. The final assay volume in the tube was 1750 μL. We started the reaction by adding 45 μL of 10 mM RuBP to the tube, split the mixture into five tubes, and stopped the reaction after 1, 2, 3, 4, or 5 mins by adding 0.5 N HCl to each tube. We added KOH to each reaction tube to adjust the pH to about pH 7.8 and added to the tubes equal amounts of freshly mixed 2PGA colorimetric cocktail that we prepared from a 2-phosphoglycerate assay kit (ab174097, Abcam), mixed all tubes well, and moved the tubes to an opaque box. We measured OD570nm after 40 min for each of the tubes and calculated the 2PGA..., , # Photorespiratory Pathway Data

[https://doi.org/10.5061/dryad.gb5mkkwwn](https://doi.org/10.5061/dryad.gb5mkkwwn)

This dataset contains data from experiments measuring the activity of Rubisco and malic enzyme.

## Description of the data and file structure

All data are in CSV format.
Oxygenation data (OxygenData.csv and TobaccoNadpNadph6PGOxyData.csv) were measured on a FireSting O2 optical oxygen and temperature sensor using a needle-type micro-optode as described in the paper. The columns are as follows:
time: Time in seconds, measured from the start of the experiment.  For experiments with non-ambient oxygen levels, negative times indicate a period prior to starting the experiment for measuring background.
oxygen: Measured level of dissolved oxygen in mg/L.
id: Unique identifier for each experiment.
date (TobaccoNadpNadph6PGOxyData.csv only): Date on which the experiment was performed, for pairing purposes.
plant: Either the plant species from which Rubisco was purified, or \"Blan...