Novel alkalistable α-carbonic anhydrase from the polyextremophilic bacterium Bacillus halodurans: characteristics and applicability in flue gas CO2 sequestration

Faridi, Shazia; Satyanarayana, T.

Novel alkalistable α-carbonic anhydrase from the polyextremophilic bacterium Bacillus halodurans: characteristics and applicability in flue gas CO2 sequestration

2016

Faridi, Shazia | Satyanarayana, T.

The emissions of CO₂ into the atmosphere have been constantly rising due to anthropogenic activities, which have led to global warming and climate change. Among various methods proposed for mitigating CO₂ levels in the atmosphere, carbonic anhydrase (CA)-mediated carbon sequestration represents a greener and safer approach to capture and convert it into stable mineral carbonates. Despite the fact that CA is an extremely efficient metalloenzyme that catalyzes the hydration of CO₂ (CO₂ + H₂O ↔ HCO₃ ⁻ + H⁺) with a kcat of ∼10⁶ s⁻¹, a thermostable, and alkalistable CA is desirable for the process to take place efficiently. The purified CA from alkaliphilic, moderately thermophilic, and halotolerant Bacillus halodurans TSLV1 (BhCA) is a homodimeric enzyme with a subunit molecular mass of ~37 kDa with stability in a broad pH range between 6.0 and 11.0. It has a moderate thermostability with a T₁/₂ of 24.0 ± 1.0 min at 60 °C. Based on the sensitivity of CA to specific inhibitors, BhCA is an α-CA; this has been confirmed by nucleotide/amino acid sequence analysis. This has a unique property of stimulation by SO₄ ²⁻, and it remains unaffected by SO₃ ²⁻, NOx, and most other components present in the flue gas. BhCA is highly efficient in accelerating the mineralization of CO₂ as compared to commercial bovine carbonic anhydrase (BCA) and is also efficient in the sequestration of CO₂ from the exhaust of petrol driven car, thus, a useful biocatalyst for sequestering CO₂ from flue gas.

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