Factors Controlling Induction of External Carbonic Anhydrase and Change in K_<1/2>(CO_2) of Photosynthesis in Chlorella regularis

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Transfer of algal cells of Chlorella regularis from 3% CO_2 in air into ordinary air in the light increased external carbonic anhydrase (CA) activity as well as photosynthetic affinity for CO_2 by several-fold within 2h. Since no noticeable difference was observed in CA activity between intact cells and cell homogenates, CA seemed to be mainly localized on the cell surface. Changes in CA activity and K_<1/2>(CO_2) of photosynthesis were not observed in the dark. CA induction was 50% -inhibited by incubation with 10μM DCMU during adaptation of high-CO_2 cells to air, whereas it was considerably suppressed when high-CO_2 cells preincubated with DCMU in the light for 6h or without DCMU in the dark for 24h were used. The change in K_1/2(CO_2) of photosynthesis was only slightly affected by DCMU. Uncoupler like carbonylcyanide-m-chlorophenyl-hydrazone (CCCP) and inhibitors of mitochondrial respiration (KCN plus salicylhydroxamic acid) suppressed CA induction during adaptation of high-CO_2 cells to low CO_2 conditions. These results suggest that photosynthesis is not essential for CA induction in Chlorella regularis when some amounts of photosynthetic products are previously stored in the cells and respiration is active. A decrease in K_1/2(CO_2) of photosynthesis during adaptation from high to low CO_2 was mostly independent on photosynthesis. However, light is essential for both phenomena.
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