FAST INDUCTION OF HIGH-AFFINITY HCO3- TRANSPORT IN CYANOBACTERIA

The induction of a high-affinity state of the CO2-concentration mechan ism was investigated in two cyanobacterial species, Synechococcus sp. strain PCC7002 and Synechococcus sp. strain PCC7942. Cells grown at hi gh CO2 concentrations were resuspended in low-CO2 buffer and illuminat ed in the presence of carbonic anhydrase for 4 to 10 min until the ino rganic C compensation point was reached. Thereafter, more than 95% of a high-affinity CO2-concentration mechanism was induced in both specie s. Mass-spectrometric analysis of CO2 and HCO3- fluxes indicated that only the affinity of HCO3- transport increased during the fast-inducti on period, whereas maximum transport activities were not affected. The kinetic characteristics of CO2 uptake remained unchanged. Fast induct ion of high-affinity HCO3- transport was not inhibited by chlorampheni col, cantharidin, or okadaic acid. In contrast, fast induction of high -affinity HCO3- transport did not occur in the presence of K252a, stau rosporine, or genistein, which are known inhibitors of protein kinases . These results show that induction of high-affinity HCO3- transport c an occur within minutes of exposure to low-inorganic-C conditions and that fast induction may involve posttranslational phosphorylation of e xisting proteins rather than de novo synthesis of new protein componen ts.