The influence of some cations on an adenosine triphosphatase from peripheral nerves.

concentratio&. Normal conditions are restored by an outward transport of the sodium ions, and this process requires energy because the efflux takes place against an electrochemical gradient. The mechanism of this transport is not known. In experiments with giant axons from Sepia officinalic and from l ligoforbesi, HoIu .iN 1 Nl) KE\NES2 found that dinitrophenob, azide and cyanide inhibit the active transport of sodium ions out of the nerve; this inhibition is revetsible. In the concentrations used all three substances also inhibit the oxydative phosphorybation which takes place in mitochondria; dinitrophenol and azide do so through an uncoupling of the phosphotylation 4, and cyanide through an inhibition of the oxydation5. CALDWELI observed correspondingly that addition of these substances, in the concentrations used by HODGKIN AND KE\NES, led to a reduction of the content of energy-rich phosphate esters in the axoplasm ofgiant axons. This seems to mdicate that energy-rich phosphate esters are somehow involved in the active transport of sodium ions out of the nerve fibres. In this connexion it is of interest that LIBET7 and ABOOD ANt) Gn Rn8 weie able to demonstrate an adenosine triphosphatase (ATPase) in the sheath of giant axons. A further study on the ATPase in nerves and its possible robe in the active outward transport of sodium ions seems warranted. According to LIBET, the ATPase in the sheath ofgiant axons is calcium-activated, while the experiments by MooD AND GERARD suggest that it is activated by magnesium and located in submicroscopic particles. In peripheral nerves from the rat the latter authors found both a calciumand a magnesium-activated ATPase. The calcium-activated enzyme was predominantly bocated in the mitochondria, while the magnesium-activated, as in giant axons, was mainly located in the submicroscopic particles. Giant axons were not available to us. In preliminary experirnents we found that a homogenate of leg nerves from the shore crab (Carcinus inaenas) contained both a calciumand a magnesium-activated ATPase, and that their localization was sirnilai to that of the ATPase found by AB0OD AND GERARD in rat-nerve homogenates. For our study we have chosen the magnesium-activated enzyme, because it resembles the magnesium-activated ATPase from the sheath of giant axons in that it is located in submicroscopic particles. The present investigation is concerned with the effect on the enzyme activity exerted by the cations normally present in the tissue-sodium , potassium , magnesium and calcium. AUTHOR COMMENTARY