Membranes are highly desirable for separating gases in life-support applications. They are small, light, efficient, selective and require little operational or physical maintenance. Facilitated transport membranes have particularly high flux and selectivity.We created enzyme-based facilitated transport membranes using isozymes and mutants as immobilized arrays alone and in conjunction with polymeric membranes. The enzyme operates efficiently at the low CO2 concentrations encountered in respiratory gases and can bring CO2 to near ambient levels. CO2 flux is greatly enhanced and selectivities for CO2 over O2 of 200:1 or greater are possible. The enzymes are robust and stable for long periods under a variety of storage and use conditions.