Carbonylation of oxyhemoglobin solution (HbO₂→ HbCO) using a membrane oxygenator

Abstract

 In the purification process of hemoglobin (Hb) from red blood cells, we stabilized Hb as carbonylhemoglobin (HbCO) against pasteurization at 60°C. In this study, the process of carbonylation (HbO₂→ HbCO) was tested with a membrane oxygenator (CX-II08; membrane area, 0.8 m²; maximum circulation rate, 1.2 l/min) under the conditions of a solution flow rate of 100–1000 ml/min and a CO gas flow rate of 30–100 ml/min. Comparing the overall O₂ transfer coefficient of carbonylation with that of deoxygenation (N₂ flow) revealed that the resistance to O₂ transfer of carbonylation was about 35 times smaller, indicating that carbonylation hindered O₂ rebinding (deoxyHb → HbO₂). On the other hand, the O₂ released in the course of carbonylation hindered carbonylation at the beginning, because rebinding of O₂ is competitive with carbonylation. The time required for carbonylation was significantly shortened from 1000 to 150 s when the solution flow rate was increased from 50 to 400 ml/min; however, the CO gas flow rate did not affect it very much. Increasing the Hb concentration from 7.5 to 15 g/dl accelerated carbonylation by 1.3 times. Even though further study is necessary to select a suitable polymer membrane to avoid protein adsorption, a membrane oxygenator will be effective for the large-scale carbonylation of Hb as a starting material of HbV in the production process.