The molecular machine for driving the coupled transports of Na+ and K+ is an (Na++K+)-activated ATPase

Lectin-binding receptors, Na+,K(+)-ATPase, and acetylcholinesterase on immunocyte plasma membrane of Limulus polyphemus

Plasma membrane receptors are crucial for nonself tissue recognition. Using concanavalin A (Con A), wheat germ agglutinin, peanut agglutinin, soybean agglutinin (SBA), and winged pea agglutinin, five lectin-binding receptor molecules have been recognized on the plasma membrane of the granulocyte (immunocyte) of the horseshoe crab, Limulus polyphemus. Only Con A and SBA caused capping of surface receptors. On the basis of the known functions of these lectin-binding receptor molecules in other invertebrates and vertebrates, their roles in phagocytosis, encapsulation, signaling, and possibly in complement pathway activation are postulated. In addition to lectin-binding receptors, Na+,K(+)-ATPase and acetylcholinesterase were detected on the plasma membrane. Because Limulus dates back to some 200 million years, the antiquity of these molecules is suggested. Furthermore, some of the lectin-binding surface receptors have the potential to be used as markers to separate different kinds of hemocytes in higher arthropods and to distinguish between normal and neoplastic cells in humans.

Detergent effects of kinetic properties of (Na+ +K+)-ATPase from kidney membranes

Studies on (Na+ +K+)-ATPase generally employ detergents such as SDS and deoxycholate. Under such conditions, the purified enzyme possesses high specific activity. The (Na+ +K+)-ATPase from kidney membranes was unmasked by deoxycholate and SDS as described by Jłrgensen and its kinetic properties were studied. The results suggest that these detergents induce some irreversible alterations in the kinetic properties of the native enzyme. Another detergent, saponin, unmasked the (Na+ +K+)-ATPase as effectively as did SDS, but it seems to affect the kinetic properties of the native enzyme to a lesser extent.

On the kinetics of acetylcholine at the synapse

Electrophysiologic, morphologic, and biochemical definitions of the synapse will be correlated spatially and temporally. Postsynaptic fatigue and facilitation follow oscillations of the free pool of acetylcholine, predicted by the kinetic theory and observed at the electric organ of Torpedo marmorata. The underlying thermodynamic instability exhibits properties of the Na+--K+-dependent hydrolysis of adenosine triphosphate and represents a necessary condition for synaptic memory.