Reversible inhibition of mammalian brain acetylcholinesterase and sodium potassium-stimulated adenosine triphosphatase by cyclopropane

Membrane-bound and purified forms of acetylcholinesterase (AChE) derived from beef brain caudate nucleus tissue were inhibited reversibly by cyclopropane at low gas pressures (0.025 to 0.25 atm). Inhibition followed mixed kinetics which suggested interactions of the anesthetic gas with both active sites(s) and other sites on the enzyme molecule. At gas pressures of 1 atm and higher, cyclopropane inhibited membrane-bound and solubilized preparations of brain Na +-K +-ATPase without affecting Mg 2+-ATPase activity. This inhibition was reversible, followed uncompetitive kinetics and was not due to pressure per se. AT 32P-labeling experiments suggested that cyclopropane inhibited Na +-K +ATPase at or before the phosphorylation step in the enzyme reaction cycle.