Two molecular forms of (Na+ + K+)-stimulated ATPase in brain. Separation, and difference in affinity for strophanthidin.

The brain contains two distinct molecular forms of the (Na,K)-ATPase (sodium and potassium ion-stimulated adenosine triphosphatase). They can be resolved by gel electrophoresis in sodium dodecyl sulfate, and can be identified by sodium-dependent, potassium-sensitive phosphorylation by [gamma-32P]ATP. They are present in the brain of every animal species examined, while only one molecular form is detected in the other organs examined. They are located in different kinds of cells within the brain, and can be physically separated while fully active by gentle tissue fractionation procedures. One is the only (Na,K)-ATPase of brain non-neuronal cells (astrocytes), while the other is the only (Na,K)-ATPase of axolemma (plasma membrane of myelinated axons). They differ in at least one kinetic parameter: the affinity for the specific inhibitor strophanthidin. They have similar one-dimensional peptide maps, but differ in their sensitivity to digestion by trypsin and in the number or reactivity of sulfhydryl groups. It is anticipated that they will be found to play functionally different roles in the complex ion transport mechanisms of the brain.