Effects of Cadmium on Carbonic Anhydrase and Activities Dependent on Electron Transport of Isolated Chloroplasts

Abstract

Low concentrations of Cadmium inhibit the electron transport and CO₂ fixation reactions of isolated chloroplasts. CO₂ fixation is more sensitive to Cd than electron transport and dark pre-incubation increases the degree of toxicity to both. Carbonic anhydrase, an enzyme associated with CO₂ fixation, is very sensitive to Cd either when applied directly to partially purified preparations of the enzyme or when enzyme preparations are obtained from intact chloroplasts previously exposed to Cd. Strong inhibition occurs at Cd concentrations lower than those required to inhibit any of the electron transport dependent reactions studied. These results are interpreted as evidence that carbonic anhydrase is one of the most sensitive sites of Cd action in isolated chloroplasts.