Affinity of RuBP Carboxylases for Carbon Dioxide and Inhibition of the Enzymes by Oxygen

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Abstract
Ribulose bisphosphate carboxylase (E.C.4.1.1.39) was purified from leaves of Triticum aestivum, Hordeum vulgare, Spinacea oleracea, Petroselinum crispum, salad mustard-most likely Brassica napus, Helianthus annuus, Solanum tuberosum, Beta vulgaris, Lolium perenne, Equisetum arvense, Zea mays, Ginkgo biloba, Pteris aquilina, Salix babylonica, Chamaecyparis lawsoniana and Atrichum undulatum by density gradient centrifugation and gel filtration or by ammonium sulphate fractionation, density gradient centrifugation, ion-exchange chromatography and gel filtration. Purified enzymes were freeze-dried and then stored at 0 °C to 4 °C. Portions of each enzyme preparation were reactivated at 25 °C for 5 h in the presence of 10 mM HCO2 and 20 mM MgCl2-RuBP carboxylase activities were measured at four different concentrations of CO2 at 25 °C and pH 8.2 in solutions equilibrated with pure nitrogen or air (21% O2, 79% N2). Km(CO2), Vmax and K1(O2) values were computed from the results. Significant differences were found in the Km(CO2) values for enzymes isolated from different species. Sensitivity of the enzymes to oxygen was less variable.