Fig. 4.

The relationship between the energies of activation (∆H_a) for the Rubisco maximum carboxylase turnover rate ($k_{cat}^c$) and the Rubisco specificity factor for CO₂/O₂ (S_c/o) in liquid phase across domains of life and photosynthetic and ecological groupings of plants (symbols as in Fig. 3). Data were separately fitted by linear regressions across domains of life (all plants averaged; solid line, r²=0.952, P<0.01) and across all groupings (plant functional and photosynthetic groupings, C₃ cool and warm and C₄, separately considered; dashed line, r²=0.846, P<0.01). In Rhodophyta, the value of ∆H_a for S_c/o is from Galdieria partita, while that of ∆H_a for $k_{cat}^c$ is from Cyanidium caldarium. For the other phylogenetic groups, data correspond to averages±SE from different numbers of species (Table 3 for data sources). Data for Thermosynechococcus elongatus (Cyanobacteria) with vastly different Rubisco kinetics (Figs 1 and 2) were not considered in the regression analysis.