Specific inactivation of alpha (+) molecular form of (Na+ + K+)-ATPase by pyrithiamin.

We have recently reported that pyrithiamin inhibits the activity of (Na+ + K+)-ATPase derived from neuronal but not non-neuronal tissue. In view of the recent demonstration that there are two molecular forms of (Na+ + K+)-ATPase in brain, the present study has examined which form of the enzyme is selectively inhibited by pyrithiamin. Experiments with sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the treatment with pyrithiamin decreased the phosphorylation by [gamma-32P]ATP of alpha (+) in a dose-dependent manner while it had little effect on that of alpha. Furthermore, the treatment with pyrithiamin changed the sensitivity of the enzyme to ouabain and N-ethylmaleimide. The specificity of the action of pyrithiamin for alpha (+) was further examined in the developing rat brain (Na+ + K+)-ATPases and peripheral (Na+ + K+)-ATPases from various animals. The molecular form of rat brain (Na+ + K+)-ATPase was primarily alpha on the 14th day of gestation, while it was mainly alpha (+) on the 18th day of gestation and postnatal age. The enzyme from 14-day fetal rat brain was resistant to pyrithiamin inhibition more than other brain enzymes. In cardiac and renal (Na+ + K+)-ATPases from various animals, only the alpha molecular form was found except for dog cardiac preparation which contained alpha (+) and alpha. Pyrithiamin inhibited dog cardiac enzyme activity, while it exerted only minimal inhibition on other peripheral enzymes. It is concluded that pyrithiamin selectively inactivates the alpha (+) molecular form of (Na+ + K+)-ATPase.