Carbonic anhydrase and photosynthesis

Abstract

Preliminary exps. have failed to demonstrate the presence of carbonic anhydrase in ground leaf tissues, throwing doubt on the view that CO2 becomes hydrated before reacting with chlorophyll. In photosynthesis, which may proceed at a rate 10-20 times that of respiration, the CO2 entering in solution must be hydrated if used as H2CO3. Calculations from data in the literature of the uncatalyzed rate of hydra-tion of CO2 in Hormidium, Sinapis, Helianthus and Pelargonium give values far below the observed rates of photosynthesis. If there proves to be no anhydrase in leaf tissue, CO2 must be reduced rather than H2CO., and the general photosynthetic equation of van Niel, CO2 + 2H2A[forward arrow]CH2O + H2O + 2A, where A is the chlorophyll nucleus, would then apply to green plants.