The CO2/O2specificity of ribulose 1,5-bisphosphate carboxylase/oxygenase

✍ Scribed by Douglas B. Jordan; William L. Ogren

• Publisher: Springer-Verlag
• Year: 1984
• Tongue: English
• Weight: 623 KB
• Volume: 161
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00398720

✦ Synopsis

The substrate specificity factor, VcKo/ V o Kc, of spinach (Spinacia oleracea L.) ribulose 1,5-bisphosphate carboxylase/oxygenase was determined at ribulosebisphosphate concentrations between 0.63 and 200 gM, at pH values between 7.4 and 8.9, and at temperatures in the range of 5 ~ C to 40 ~ C. The CO2/O 2 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 V~ [Vmax (CO2)], which increased by factors of about 10 and 20, respectively, over the temperature range examined. In contrast, K o [Ki (02)] was unchanged and V o [Vmax (02) ] increased by a factor of 5 over these temperatures. The CO 2 compensation concentrations (F) were calculated from specificity values obtained at temperatures between 5 ~ C and 40 ~ C, and were compared with literature values of F. Quantitative agreement was found for the calculated and measured F values. The observations reported here indicate that the temperature response of ribulose 1,5-bisphosphate carboxylase/ oxygenase kinetic parameters accounts for twothirds of the temperature dependence of the photorespiration/photosynthesis ratio in C 3 plants, with the remaining one-third the consequence of differential temperature effects on the solubilities of CO 2 and 02.