ABSTRACT
Several isoforms of carbonic anhydrases (CAs), soluble and membrane-bound ones, were discovered in the chloroplasts of higher plants. By now, two soluble CAs, α-CA1 and β-CA1, are known to be situated in the chloroplast stroma, and one soluble CA belonging possibly to the β-CA family was found in the thylakoid lumen. α-CA4 was identified among the proteins of the thylakoid membrane. At the same time, at least three sources of CA activity in the thylakoid membrane were revealed. The thylakoid membrane fragments enriched with photo system II (PSII membranes) possess two such sources. One of them was detected as a low-molecular-mass protein in the course of the native electrophoresis of the PSII membranes treated with n-dodecyl-β-maltoside. The other was disclosed among high-molecular-mass proteins of the PSII core complex. Besides the different molecular mass, these CAs demonstrate different sensitivity to the different specific CA inhibitors, sulfonamides. One source of CA activity was revealed in the fragments of thylakoid membrane enriched with photosystem I (PSI). This CA activity was equally susceptible to both lipophilic and hydrophilic sulfonamides. The possible functions of thylakoid CAs are discussed.
