Putrescine

l‐Lysine and 5‐aminopentanoate were purchased from Tokyo Chemical Industry Co., Ltd. (https://www.tcichemicals.com); cadaverine, δ‐valerolactam, 1‐formylpyrrolidine, 1,9‐diaminononane and β‐nicotinamide adenine dinucleotide (NAD⁺) were obtained from Sigma‐Aldrich (http://www.sigmaaldrich.com); 5‐aminopentanal was acquired from Activate Scientific (https://shop.activate-scientific.com); [α‐¹⁵N]‐l‐Lysine and [ε‐¹⁵N]‐l‐lysine were purchased from Cambridge Isotope Laboratories Inc. (http://www.isotope.com); l‐ornithine, putrescine and all LC‐MS‐grade buffers used for LC‐MS were purchased from FUJIFILM Wako Pure Chemical Co. (http://www.wako-chem.co.jp).

To incorporate atmospheric CO₂ into polyamine solutions, solutions (2 ml) containing piperazine (Wako Pure Chemicals, Osaka, Japan) and biogenic polyamines (putrescine, spermidine, cadaverine and spermine; Wako Pure Chemicals, Osaka, Japan) each at 0.1 M were added to multidishes (24 wells, diameter of 15 mm), which stood for 48 hours at 20 °C. The resultant polyamine solutions at pH 8.9–9.1 were used as carbonate sources in Rubisco assays.
To activate Rubisco, the enzyme was preincubated in the presence of the polyamine solutions retaining CO₂ instead of NaHCO₃ solutions^{33 (link)}.
To investigate the time-dependent changes in Rubisco activity, solutions (2 ml) containing 0.1 M piperazine were added to multidishes (24 wells, diameter of 15 mm), which stood for 0, 5, 7 and 48 hours at 20 °C. The resultant piperazine solutions at pH 8.9–9.1 were used as carbonate sources in Rubisco assays. Ten millimolar solutions of NaHCO₃ served as positive controls.