Communication Simple Determination of the CO2/02 Specificity of Ribulose- 1,5-Bisphosphate Carboxylase/Oxygenase by the Specific Radioactivity of [14CjGlycerate 3-Phosphate1

A new method is presented for measurement of the C02/02 specificity factor of ribulose-1,5-bisphosphate carboxylase/oxy-genase (Rubisco). The [14C]3-phosphoglycerate (PGA) from the Rubisco carboxylase reaction and its dilution by the Rubisco oxygenase reaction was monitored by directly measuring the specific radioactivity of PGA. '4CO2 fixation with Rubisco occurred under two reaction conditions: carboxylase with oxygenase with 40 micromolar CO2 in 02-saturated water and carboxylase only with 160 micromolar CO2 under N2. Detection of the specific radioactivity used the amount of PGA as obtained from the peak area, which was determined by pulsed amperometry following separation by high-performance anion exchange chromatography and the radioactive counts of the [14C]PGA in the same peak. The specificity factor of Rubisco from spinach (Spinacia oleracea L.