Structure and catalytic mechanism of the beta-carbonic anhydrases.

The beta-carbonic anhydrases (beta-CAs) are a diverse but structurally related group of zinc-metalloenzymes found in eubacteria, plant chloroplasts, red and green algae, and in the Archaea. The enzyme catalyzes the rapid interconversion of CO(2) and H(2)O to HCO(3)(-) and H(+), and is believed to be associated with metabolic enzymes that consume or produce CO(2) or HCO(3)(-). For many organisms, beta-CA is essential for growth at atmospheric concentrations of CO(2). Of the five evolutionarily distinct classes of carbonic anhydrase, beta-CA is the only one known to exhibit allosterism. Here we review the structure and catalytic mechanism of beta-CA, including the structural basis for allosteric regulation.