The production of adenosine triphosphate in perfused giant axons of Loligo.

1. The light production by squid giant axons perfused with solutions containing extract of firefly tails has been studied to give information about the production of ATP in such axons.2. An initial flash occurs when the perfusion fluid first enters the fibre. There is a secondary production of light, noticeable when the perfusion is halted, providing glutamate or aspartate are present in the perfusion medium.3. There is no secondary light production if glutamate is replaced by sulphate, succinate or alpha-ketoglutarate in the perfusion fluid.4. Ouabain has no effect whereas cyanide and oligomycin both block the secondary light production, the latter irreversibly.5. When the sodium outside the fibre is replaced by lithium or choline the secondary light production is often reduced and occasionally abolished.6. A raised internal sodium does not enhance secondary light production.7. The secondary light production is dependent upon the concentration of AMP in the perfusion solution.8. Fresh axoplasm generates a powerful light on immersion in perfusion fluid whereas dialysed axoplasm, even in the presence of added glutamate, generates no light whatever.9. The evidence, on balance, suggests that, under the conditions of the experiments described, there is no detectable reversal of active transport in perfused nerve fibres but that there is an enzyme system, probably membrane bound, capable of generating ATP from glutamate or aspartate and AMP by oxidative phosphorylation. The enzyme system can be inhibited by the replacement of external sodium.