Abstract
The review presents data on the location, nature, properties, number, and expression of carbonic anhydrase genes in the photosynthesizing cells of C3 plants. The available data about the presence of carbonic anhydrases in plasma membrane, cytoplasm, mitochondria, chloroplast stroma and thylakoids are scrutinized. Special attention was paid to the presence of carbonic anhydrase activities in the different parts of thylakoids, and on collation of sources of these activities with enzymes encoded by the established genes of carbonic anhydrases. The data are presented to show that the consistent incorporation of carbonic anhydrases belonging to different families of these enzymes forms a coherent system of CO2 molecules transport from air to chloroplasts in photosynthesizing cells, where they are included in organic molecules in the carboxylation reaction. It is discussed that the manifestation of the activity of a certain carbonic anhydrase depends on environmental conditions and the stage of ontogenesis.
Highlights
The process of CO2 incorporation into organic matter in higher plants takes places in chloroplasts, the specialized organelles of photosynthesizing cells containing thylakoids, flattened bubbles bound by a membrane where the ATP and NADPH-producing photosynthetic electron transport chain (PETC) is located
Mitochondrial β-CA6 in higher plants may perform the same role as Carbonic anhydrase (CA) CAH4 and CAH5 in the Chlamydomonas reinhardtii mitochondrial matrix, which, as shown in the study by Giordano et al [39], catalyze the conversion of carbon dioxide formed in the tricarboxylic acid cycle into bicarbonate, which is later used in the NH4 + assimilation reaction, the products of which are used in protein synthesis
While considerable progress has been made in understanding CA functions in such highly specialised animal tissues as blood and kidneys, and much has been achieved in identifying the functions of these enzymes in microalgae, progress in understanding the functions of CAs in photosynthesizing cells of higher plants where these functions appear obvious is rather slow
Summary
The process of CO2 incorporation into organic matter in higher plants takes places in chloroplasts, the specialized organelles of photosynthesizing cells containing thylakoids, flattened bubbles bound by a membrane where the ATP and NADPH-producing (during the light-dependent reaction stage of photosynthesis) photosynthetic electron transport chain (PETC) is located. Carbonic anhydrase (CA) is the enzyme that catalyzes the reaction of reversible hydration of CO2 to HCO3 − , increasing greatly the rates in both directions; the kcat can be up to 106 times higher as compared with spontaneous reaction constant, with larger acceleration of the hydration reaction These enzymes are widely distributed in living systems and present in all cells of organs and tissues of animals, including humans, as well as in ascomycetes, bacteria, algae and higher plants. CAs were attributed the role of ensuring the required conversion rate of HCO3 − molecules into CO2 , but that of transporting inorganic carbon from air to the chloroplast stroma where the Rubisco is located. We will consider data on CA presence in C3 plant photosynthesizing cell structures, as well as the proven and proposed functions of these CAs
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