Carbon Dioxide Assimilation by Leaves, Isolated Chloroplasts, and Ribulose Bisphosphate Carboxylase from Spinach

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Abstract
The relationship between rate of photosynthesis and CO2 concentration has been reinvestigated using isolated spinach (Spinacia oleracea) chloroplasts. The apparently low CO2 concentration required for half-maximal photosynthesis is shown to result partly from a ceiling imposed by electron transport. In double reciprocal plots of rate against CO2 concentration, this ceiling results in departures from linearity at high CO2 concentrations. If these rate limitations are disregarded in extrapolation the “true” CO2 concentration required for half maximal carboxylation by intact chloroplasts is approximately 46 μm (CO2).