Multiple studies have shown Rubisco to be subject to Lys-acetylation at various residues; however, conflicting reports exist about the biological significance of these post-translational modifications. One aspect of the Lys-acetylation that has not been addressed in plants generally, or with Rubisco specifically, is the stoichiometry at which these Lys-acetylation events occur. As a method to ascertain which Lys-acetylation sites on Arabidopsis Rubisco might be of regulatory importance, we purified Rubisco from leaves in both the day and night-time and performed independent mass-spectrometry based methods to determine the stoichiometry of Rubisco Lys-acetylation events.