Biochemistry and Physiology of the β Class Carbonic Anhydrase (Cpb) from Clostridium perfringens Strain 13

The carbonic anhydrase (Cpb) fromClostridium perfringens strain 13, the only carbonic anhydrase encoded in the genome, was characterized both biochemically and physiologically. Heterologously produced and purified Cpb was shown to belong to the type I subclass of the β class, the first β class enzyme investigated from a strictly anaerobic species of the domainBacteria . Kinetic analyses revealed a two-step, ping-pong, zinc-hydroxide mechanism of catalysis withKm andk cat /Km values of 3.1 mM CO2 and 4.8 × 106 s−1 M−1 , respectively. Analyses of acpb deletion mutant ofC. perfringens strain HN13 showed that Cpb is strictly required for growth when cultured in semidefined medium and an atmosphere without CO2 . The growth of the mutant was the same as that of the parent wild-type strain when cultured in nutrient-rich media with or without CO2 in the atmosphere, although elimination of glucose resulted in decreased production of acetate, propionate, and butyrate. The results suggest a role for Cpb in anaplerotic CO2 fixation reactions by supplying bicarbonate to carboxylases. Potential roles in competitive fitness are discussed.