Lipoidal membranes stabilize isolated salmon and chicken carbonic anhydrase under conditions of increased temperature and pH.

1. Solutions of purified carbonic anhydrase from chicken and salmon erythrocytes were incubated in buffer for 1 hr at 5 degrees or 22 degrees C, at pH 7.3, 7.6, 7.9 or 8.2. 2. At 22 degrees C the enzymes lost up to 25% of their ability to catalyze the CO2 hydration reaction when compared to control solutions maintained in the cold. 3. Loss of enzyme activity (approximately 50%) also occurred as pH was increased from 7.3 to 8.2. 4. The presence of lecithin vesicles or microsomes completely protected the enzymes from denaturation caused by pH changes and afforded partial protection from changes due to increased temperature.