Table 3.
In vitro Rubisco kinetic parameters and their temperature response in D. antarctica and C. quitensis
The Rubisco Michaelis–Menten constant affinity for CO2 under 21% O2 (Kcair), the maximum carboxylase catalytic turnover rate (kcatc), the carboxylase catalytic efficiency (kcatc/Kcair), and the specificity factor (Sc/o). For each parameter, the scaling constant (c) and the activation energy (ΔHa) are shown.
| Assay temperature | D. antarctica | C. quitensis | ||||||
|---|---|---|---|---|---|---|---|---|
| K c air (µM) | k cat c (s–1) | k cat c/Kcair (s–1 µM–1) | S c/o (mol mol–1) | K c air (µM) | k cat c (s–1) | k cat c/Kcair (s–1 µM–1) | S c/o (mol mol–1) | |
| 5 ºC | 10.9 ± 1.2 a* | 0.4 ± 0.1 a* | 0.04 ± 0.00 a | 167.5 ± 2.9 c | 6.9 ± 0.4 a* | 0.2 ± 0.1 a* | 0.03 ± 0.00 a | 172.4 ± 2.0 c |
| 15 ºC | 14.7 ± 0.8 a* | 1.4 ± 0.2 a | 0.09 ± 0.01 ab | 151.3 ± 4.5 b* | 11.1 ± 0.6 b* | 1.1 ± 0.1 b | 0.10 ± 0.01 b | 129.8 ± 3.7 b* |
| 25 ºC | 23.4 ± 1.8 b | 4.1 ± 0.8b | 0.18 ± 0.04 b | 99.5 ± 4.8 a | 18.7 ± 0.4 c | 3.8 ± 0.3 c | 0.20 ± 0.01 c | 97.1 ± 2.4 a |
| c | 14.5 ± 1.8 | 33.2 ± 0.8 | 18.4 ± 2.5 | –1.7 ± 0.6 | 17.1 ± 0.7 | 41.0 ± 2.7 | 20.9 ± 0.2 | –3.2 ± 0.5 |
| ΔHa (kJ mol–1) | 28.2 ± 4.4 | 78.8 ± 1.5* | 49.9 ± 5.6 | –15.9 ± 1.4 | 35.2 ± 1.6 | 98.3 ± 6.6* | 55.6 ± 0.5 | –19.3 ± 1.2 |
Different letters indicate statistically significant differences among assay temperatures in each species, and an asterisk denotes statistically significant differences between D. antarctica and C. quitensis for each assay temperature (P<0.05).
Values are means ± SE (n=3–6).
For comparative purposes, we also measured the kinetic parameters at 25 ºC in Rubisco from wheat (Triticum aesticum ‘Cajerne’). The values were as follows: Kcair=16.0 µM; kcatc=2.2 s−1; kcatc/Kcair=0.14 s–1 µM–1; Sc/o=101.1 mol mol–1.