Extrinsic Photosystem II Carbonic Anhydrase in Maize Mesophyll Chloroplasts

Abstract

One form of carbonic anhydrase (CA) has been observed in maize (Zea mays) thylakoids and photosystem II (PSII)-enriched membranes. Here, we show that an antibody produced against a thylakoid lumen-targeted CA found in Chlamydomonas reinhardtii reacts with a single 33-kD polypeptide in maize thylakoids. With immunoblot analysis, we found that this single polypeptide could be identified only in mesophyll thylakoids and derived PSII membranes, but not in bundle sheath thylakoids. Likewise, a CA activity assay confirmed a large amount of activity in mesophyll, but not in bundle sheath membranes. Immunoblot analysis and CA activity assay showed that the maximum CA can be obtained in the supernatant of the PSII-enriched membranes washed with 1 m CaCl 2 , the same procedure used to remove all extrinsic lumenal proteins from PSII. Because this CA reacts with an antibody to lumen-directed CA in C. reinhardtii, and because it can be removed with 1 m CaCl 2 wash, we refer to it tentatively as extrinsic CA. This is to distinguish it from another form of CA activity tightly bound to PSII membranes that remains after CaCl 2 wash, which has been described previously. The function of extrinsic CA is not clear. It is unlikely to have the same function as the cytoplasmic CA, which has been proposed to increase the HCO 3 Ϫ concentration for phosphoenolpyruvate carboxylase and the C 4 pathway. We suggest that because the extrinsic CA is associated only with thylakoids doing linear electron flow, it could function to produce the CO 2 or HCO 3 Ϫ needed for PSII activity.

Photosystem II associated carbonic anhydrase activity in higher plants is situated in core complex

“…With both PSII membrane preparations, from pea and wheat, the CA-activities of supernatants after sedimentation of membranes treated either with Triton X-100 or CaCl 2 were not detected. Lu and Stemler [4] observed CA activity in the supernatants after the similar salt treatment of PSII membranes, after desalting of these supernatants. The absence of CA activity in the supernatants, that were not desalted ( Table 1), showed that an increase of CA activity in Fig.…”

“…The Mn-stabilizing protein 33 kD was considered as a possible carrier of the CA activity [4]. However, this protein passes into solution in the course of CaCl 2 treatment of PSII membranes [16].…”

“…The literature data show that substantial part of the thylakoid CA activity is structurally associated with photosystem II (PSII) [3][4][5]. Elucidation of the role of CA activity in PSII requires ascertainment of its exact localization in the photosystem.…”

Photoassembly of the water-oxidizing complex in photosystem II

“…A low level of carbonic anhydrase (CA) activity, more than 10 3 slower than typical Zn 2+ -CA, has been found to be intrinsic to oxygenevolving PS II membranes [69,70]. A soluble CA activity was found associated with the 33 kDa extrinsic protein of PS II (PsbO) and depends on the concentration of Mn 2+ and Cl − .…”

Carbonic anhydrase activity of integral-functional complexes of thylakoid membranes of spinach chloroplasts

“…There is an evidence that PS II-associated CA generates bicarbonate ions at a rate sufficient to bound protons released in the inner space of thylakoid in the process of photosynthetic oxidation of water [9]. Hence, CA prevents acidic denaturation of manganese cluster of PS II, as critical increase in local H + concentration may damage the active centers of the complex and result in their destruction with manganese release in liquid environment [10,11].…”