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영어

Photosynthesis in aquatic environments may be limited due to the low solubility and slow diffusion rate of CO2 in water. Most unicellular algae have evolved a CO2-concentrating mechanism (CCM) to compensate for this CO2 limitation. Carbonic anhydrase (CA) is a zinc-containing enzyme catalyzing reversible hydration of carbon dioxide: CO2+H2O ↔ HCO−� 3+H+, has been suggested to play a crucial role in the CCM as well as in the CA-mediated calcification found in eukaryotic algae and protists. The green algae Chlamydomonas reinhardtii adapts to low Ci conditions by inducing various forms of CAs, which help concentrate Ci internally, resulting in much higher levels than can be obtained by diffusion alone. In C. reinhardtii, two different intracellular CAs have been identified, a low CO2-induced mitochondrial CA and a constitutively expressed CA located in the chloroplast thylakoid membranes. In the present talk, I’l briefly introduce a thylakoid-associated CA, which is localized in photosystem (PS) II membrane fractions and plays a pivotal role in determining the viability of low CO2 intolerant mutants in atmospheric CO2 through involvement in CCM.