Abstract
When cells of Anacystis nidulans strain R2 grown under high CO(2) conditions (3%) were transferred to low CO(2) conditions (0.05%), their ability to accumulate inorganic carbon (C(i)) increased up to 8 times. Cytoplasmic membranes (plasmalemma) isolated at various stages of low CO(2) adaptation were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. There was a marked increase of a 42-kilodalton polypeptide in the cytoplasmic membrane during adaptation; a linear relationship existed between the amount of this polypeptide and the C(i)-accumulating capability of the cells. No significant changes were observed during this process in the amount of other polypeptides in the cytoplasmic membranes or in the polypeptide profiles of the thylakoid membranes, cell walls, and soluble fractions. Spectinomycin, an inhibitor of protein biosynthesis, inhibited both the increase of the 42-kilodalton polypeptide and the induction of high C(i)-accumulating capability. The incorporation of [(35)S]sulfate into membrane proteins was greatly reduced during low CO(2) adaptation. Radioautograms of the (35)S-labeled membrane proteins revealed that synthesis of the 42-kilodalton polypeptide in the cytoplasmic membrane was specifically activated during the adaptation, while that of most other proteins was greatly suppressed. These results suggested that the 42-kilodalton polypeptide in the cytoplasmic membrane is involved in the active C(i) transport by A. nidulans strain R2 and its synthesis under low CO(2) conditions leads to high C(i)-transporting activity.