INHIBITION OF Mg- AND Mg, Na, K-ACTIVATED ADENOSINE TRIPHOSPHATASE ACTIVITY BY L-ASCORBIC ACID AND L-CYSTEINE

Abstract

It is now commonly postulated that the electrical excitability of neural cells depends on the concentration gradients of Na⁺ and K⁺ across the cell membrane and the gradients are maintained by active cation transport system. Further, a membrane-bound, Na⁺ and K⁺-stimulated and ouabain-sensitive adenosine triphosphatase (Na-K-ATPase) has been proved to be involved in the active cation transport system in the brain as well as in many other tissues (1). While cardiac glycosides have been well known to be specific inhibitors of Na-K-ATPase, some biogenic substances were also considered to participate in the transport mechanism. In this respect, two biogenic substances, ascorbic acid and cysteine, came to light. They were described as rather specific inhibitors of Na-K-ATPase in the electric organ of eel (2) and the liver of rat (3). The present report describes how ascorbic acid and cysteine affect Na-K-ATPase and Mg-ATPase of the rabbit brain, histochemically and biochemically. For reference the enzymes of rabbit liver were tested.