Effect of helium and heliox on glutamate decarboxylase activity

The activity of glutamate decarboxylase (GAD) in pure helium at 6.8 MPa was significantly enhanced when compared to GAD activity in air at 0.1 MPa (906 vs. 602 nmol.h-1.mg-1 protein, respectively). No significant difference was found between GAD activities in heliox at 6.8 MPa (0.87% O2 at 6.8 MPa) and in air at 0.1 MPa. On the other hand, the activities in heliox at 0.1 MPa (0.87% O2 at 0.1 MPa) and air at 0.1 MPa were significantly different (655 and 446 nmol.h-1.mg-1 protein, respectively). These data indicate that pressures up to 6.8 MPa do not affect the GAD-catalyzed synthesis of gamma-aminobutyric acid, but that the enzyme, as previously reported, is sensitive to low levels of oxygen.