Inorganic Carbon Accumulation by Chlamydomonas reinhardtii: New Proteins are made During Adaptation to Low CO(2).

When the unicellular green alga Chlamydomonas reinhardtii is placed under low CO(2) conditions it adapts by making an inorganic carbon accumulating mechanism. Algal cells were labeled with (35)SO(4) (-2) during this adaptation period and labeled proteins specific for this low CO(2) adaptation were identified. Four major proteins were preferentially synthesized under low CO(2) conditions and had M(r) of 46, 44, 37, and 20 kilodaltons. The 37 kilodalton protein is most likely the periplasmic carbonic anhydrase previously identified as being part of the inorganic carbon accumulation mechanism of C. reinhardtii. The other three proteins have not been identified. The 46 and the 44 kilodalton proteins were not synthesized by a mutant algal strain, pmp-1, which cannot grow at low CO(2) concentrations. This strain does make the 37 and 20 kilodalton proteins, however. These data suggest that at least two or three proteins in addition to the periplasmic carbonic anhydrase are part of the inorganic carbon accumulation mechanism in C. reinhardtii.