A biomimetic strategy for CO2 capture was recently proposed and extensively reviewed in the literature [1]. It is based on the use of Carbonic Anhydrase (CA) as biocatalyst to increase CO2 absorption rate in aqueous solutions. Kinetic characterization of CA forms is one of the key issues for the design of the absorption unit. The kinetics should be assessed under operating conditions as close as possible to those used in industrial processes. However, the CA kinetic assessment asks for rapid mixing techniques (e.g. stopped flow) because of the exceptional turnover (ranging between 104 and 106 s-1). Indirect measurement strategies of the CO2 absorption rate under controlled conditions of mass transfer rate were used by several authors [2, 3]. These strategy allowed to investigate the effects of temperature, solvent ionic strength and pH over wide ranges. The present contribution concerns the characterization of a protein mixture containing recombinant CA. The indirect measurements strategy was based on time-resolved measurements of gas pressure decay in a batch stirred reactor (Figure 1). The absorption rate of pure CO2 into carbonate solutions was assessed by processing the pressure timeseries. The aim of the study were: - t he assessment of the second order kinetic constant kcat/Km at 25 and 40°C. Initial carbonate concentration and carbonate conversion were changed to simulate actual solvent composition in CO2 capture units. - the protein mixture characterization in terms of long term stability at temperature between 40 and 70°C. - the role of precipitated enzyme aggregates that may be observed at enzyme concentrations larger that its solubility limit in the selected solvent Concerning the latter aim, it has been inspired by two evidences: if the time scale of enzyme precipitation is slower than that of denaturation of its structure, the protein aggregates are made by active enzymes; the contribution of dissolved CA at concentration lower than 100 mg/L is not satisfactory [4]. Hence, it is worth to try to control the activity of CA precipitated aggregates as a reliable alternative to increase enzyme loading in the reactor. Preliminary results showed that the CA kcat/Km ratio was 0.9 L/(mg s) at 25°C in NaHCO3/Na2CO3 buffer at pH 9.6. This value is similar to those assessed in previous works for bovine CA and larger than that assessed for the thermostable recombinant CA from the bacterium Sulphurhydrogenibium sp. YO3AOP1 [2]
KINETIC ASSESSMENT OF THERMOSTABLE CARBONIC ANHYDRASE FOR BIOMIMETIC CO2 CAPTURE IN CARBONATE SOLUTIONS: EFFECT OF ENZYME PRECIPITATION
Maria Elena Russo;Clemente Capasso;
2015
Abstract
A biomimetic strategy for CO2 capture was recently proposed and extensively reviewed in the literature [1]. It is based on the use of Carbonic Anhydrase (CA) as biocatalyst to increase CO2 absorption rate in aqueous solutions. Kinetic characterization of CA forms is one of the key issues for the design of the absorption unit. The kinetics should be assessed under operating conditions as close as possible to those used in industrial processes. However, the CA kinetic assessment asks for rapid mixing techniques (e.g. stopped flow) because of the exceptional turnover (ranging between 104 and 106 s-1). Indirect measurement strategies of the CO2 absorption rate under controlled conditions of mass transfer rate were used by several authors [2, 3]. These strategy allowed to investigate the effects of temperature, solvent ionic strength and pH over wide ranges. The present contribution concerns the characterization of a protein mixture containing recombinant CA. The indirect measurements strategy was based on time-resolved measurements of gas pressure decay in a batch stirred reactor (Figure 1). The absorption rate of pure CO2 into carbonate solutions was assessed by processing the pressure timeseries. The aim of the study were: - t he assessment of the second order kinetic constant kcat/Km at 25 and 40°C. Initial carbonate concentration and carbonate conversion were changed to simulate actual solvent composition in CO2 capture units. - the protein mixture characterization in terms of long term stability at temperature between 40 and 70°C. - the role of precipitated enzyme aggregates that may be observed at enzyme concentrations larger that its solubility limit in the selected solvent Concerning the latter aim, it has been inspired by two evidences: if the time scale of enzyme precipitation is slower than that of denaturation of its structure, the protein aggregates are made by active enzymes; the contribution of dissolved CA at concentration lower than 100 mg/L is not satisfactory [4]. Hence, it is worth to try to control the activity of CA precipitated aggregates as a reliable alternative to increase enzyme loading in the reactor. Preliminary results showed that the CA kcat/Km ratio was 0.9 L/(mg s) at 25°C in NaHCO3/Na2CO3 buffer at pH 9.6. This value is similar to those assessed in previous works for bovine CA and larger than that assessed for the thermostable recombinant CA from the bacterium Sulphurhydrogenibium sp. YO3AOP1 [2]I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
