Two Polypeptides in the Inner Chloroplast Envelope of Dunaliella tertiolecta Induced by Low CO₂

Abstract

Unicellular green algae have a mechanism for concentrating dissolved inorganic carbon (DIC) only when grown in low CO₂. To find proposed transporter protein(s) for DIC, we isolated intact chloroplasts from Dunaliella tertiolecta cells, separated the chloroplast envelopes by isopyknic centrifugation, and separated their polypeptides by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Two peptides of apparent molecular masses of 45 and 47 kD were constituents of the inner chloroplast envelope only if the cells had been adapted to low CO₂ in the light or grown in low CO₂. These two low CO₂-induced peptides appear to be part of the algal DIC pump.