Variations in the Rubisco specific activity (k_cat) and the ratio of carboxylase/oxygenase activity at ambient air (v_c/v_o) among higher plants

Abstract

Large variations in k_cat and the CO₂/O₂-specificity ( τ ) of Rubisco exist among enzymes from different photosynthetic species. Among them, Rubisco from higher plants have the lowest k_cat and highest τ and their variations have been small. However, we previously found a large variation in k_cat, and Galmés et al. (2005) also observed a significant variation in τ among higher plants including hemi-deciduous and evergreen trees. In this study, we examined simultaneously k_cat and v_c/v_o at 0.038%CO₂ and 21%O₂, and determined net Rubisco activity per enzyme protein at ambient air [k_cat(1-0.5_o/v_c)] from various plants. Nicotiana tabacum, Populus alba, Fagus crenata, and a few Eucalyptus species showed higher k_cat (50-70% higher than that of rice Rubisco). For v_c/v_o, P. alba, Abies Mariesii and Pinus pumila had 20% higher than rice Rubisco. The k_cat(1-0.5v_o/v_c) was the highest in P. alba, and 1.7-fold greater than that of rice Rubisco.