Carboxysome

（重定向自Carboxysomes）

Model for the structure of the carboxysome. RuBisCO and carbonic anhydrase are arranged in an enzymatic core (organized by various core proteins) and encapsulated by a protein shell.

Electron micrograph of (A) alpha-carboxysomes in Halothiobacillus neapolitanus and (B) beta-carboxysomes in Synechococcus elongatus PCC 7942, indicated by arrows

Vista del carboxisoma y estructuras bacterianas relacionadas.

Carboxysomes are bacterial organelles consisting of polyhedral protein shells filled with the enzyme Ribulose-1,5-biphosphate carboxylase/oxygenase (RuBisCO) -the predominant enzyme in carbon fixation and the rate limiting enzyme in the Calvin Cycle-and a carbonic anhydrase. Carboxysomes are thought to have evolved as a consequence of the increase in oxygen concentration in the ancient atmosphere; this is because oxygen is a competing substrate to carbon dioxide in the RuBisCO reaction. To overcome the inefficiency of RuBisCO, carboxysomes concentrate carbon dioxide inside the shell by means of co-localized carbonic anhydrase activity, which produces carbon dioxide from the bicarbonate that diffuses into the carboxysome. The resulting production of carbon dioxide near RuBisCO decreases the proportion of ribulose-1,5-bisphosphate oxygenation and thereby avoids costly photorespiratory reactions. The surrounding shell provides a barrier to carbon dioxide loss, helping to increase its concentration around RuBisCO. The carboxysome is an essential part of the carbon-concentrating mechanism (CCM).

单词	Carboxysomes
释义	Carboxysomes 英语百科 Carboxysome （重定向自Carboxysomes） Carboxysomes are bacterial organelles consisting of polyhedral protein shells filled with the enzyme Ribulose-1,5-biphosphate carboxylase/oxygenase (RuBisCO) -the predominant enzyme in carbon fixation and the rate limiting enzyme in the Calvin Cycle-and a carbonic anhydrase. Carboxysomes are thought to have evolved as a consequence of the increase in oxygen concentration in the ancient atmosphere; this is because oxygen is a competing substrate to carbon dioxide in the RuBisCO reaction. To overcome the inefficiency of RuBisCO, carboxysomes concentrate carbon dioxide inside the shell by means of co-localized carbonic anhydrase activity, which produces carbon dioxide from the bicarbonate that diffuses into the carboxysome. The resulting production of carbon dioxide near RuBisCO decreases the proportion of ribulose-1,5-bisphosphate oxygenation and thereby avoids costly photorespiratory reactions. The surrounding shell provides a barrier to carbon dioxide loss, helping to increase its concentration around RuBisCO. The carboxysome is an essential part of the carbon-concentrating mechanism (CCM).
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