The CO2/O2 specificity of ribulose 1,5-bisphosphate carboxylase/oxygenase
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- Jordan, D.B. & Ogren, W.L. Planta (1984) 161: 308. doi:10.1007/BF00398720
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The substrate specificity factor, VcKo/VoKc, of spinach (Spinacia oleracea L.) ribulose 1,5-bisphosphate carboxylase/oxygenase was determined at ribulosebisphosphate concentrations between 0.63 and 200 μM, at pH values between 7.4 and 8.9, and at temperatures in the range of 5° C to 40° C. The CO2/O2 specificity was the same at all ribulosebisphosphate concentrations and largely independent of pH. With increasing temperature, the specificity decreased from values of about 160 at 5° C to about 50 at 40° C. The primary effects of temperature were on Kc [Km(CO2)] and Vc [Vmax (CO2)], which increased by factors of about 10 and 20, respectively, over the temperature range examined. In contrast, Ko [Ki (O2)] was unchanged and Vo [Vmax (O2)] increased by a factor of 5 over these temperatures. The CO2 compensation concentrations (Γ) were calculated from specificity values obtained at temperatures between 5° C and 40° C, and were compared with literature values of Γ. Quantitative agreement was found for the calculated and measured Γ values. The observations reported here indicate that the temperature response of ribulose 1,5-bisphosphate carboxylase/oxygenase kinetic parameters accounts for two-thirds of the temperature dependence of the photorespiration/photosynthesis ratio in C3 plants, with the remaining one-third the consequence of differential temperature effects on the solubilities of CO2 and O2.
Key wordsCarbon dioxide compensation concentration Leaf photosynthesis Photorespiration Rhodospirillum Ribulose 1,5-bisphosphate carboxylase/oxygenase Spinacia (RuBPCase)
ribulose 1,5-bisphosphate carboxylase/oxygenase
CO2 compensation concentration