Role of Carbonic Anhydrase in Photosynthesis of Blue-Green Alga (Cyanobacterium)Anabaena variabilisATCC 29413

摘要

The affinity for NaHCO3(CO2) in photosynthesis ofAnabaena variabilisATCC 29413 was much higher in the cells grown under ordinary air (low-CO2cells) than in those grown in air enriched with 2–4CO2(high-CO2cells) (pH 8.0, 25°C). Ethoxyzolamide (50μM) increased theKm(NaHCO3in low-CO2cells about nine times (from 14.3 to 125), while the maximum rate of photosynthesis decreased about 20. When high-CO2cells were transferred to low-CO2conditions, carbonic anhydrase (CA) activity increased, whileKm(NaHCO3) in photosynthesis decreased from 140 to 30μM within about 5 h. The addition of CA to the suspension of both high- and low-CO2cells enhanced the rates of photosynthetic O2evolution under CO2-limiting conditions. The rate of14CO2fixation was much faster than that of H14CO3−fixation. The former reaction was greatly suppressed, while the latter was enhanced by the addition of CA. These results indicate that the active species of inorganic carbon utilized for photosynthesis was free CO2irrespective of the CO2concentration given during growth. It is suggested that CA plays an active role in increasing the affinity for CO2in photosynthesis of low-CO2cells of this blue-gree