PHYSIOLOGY OF INSECT DIAPAUSE. XII. THE MECHANISM OF CARBON MONOXIDE-SENSITIVITY AND -INSENSITIVITY DURING THE PUPAL DIAPAUSE OF THE CECROPIA SILKWORM

¹ The Biological Laboratories, Harvard University, Cambridge 38, Massachusetts

1. The heartbeat of the adult Cecropia moth is inhibited by suitable pressures of carbon monoxide, and this inhibition is reversed by light.

2. The wave-lengths which are maximally effective in reversing the CO-inhibition are in good agreement with the absorption maxima of the CO-cytochrome oxidase complex.

3. Therefore, the terminal oxidase of the adult heart may be identified as cytochrome oxidase.

4. The situation is much more complex in the case of the diapausing pupa. The latter shows a considerable capacity for anaerobic metabolism, and its heart can beat for several hours in the total absence of oxygen. Moreover, normal heartbeat continues indefinitely in the presence of oxygen pressures as low as 0.5% atm.

5. After exhaustion of the "anaerobic reserve," the pupal heart may be said to be "micro-aerophilic." Oxygen is required but a remarkably low tension suffices.

6. At ordinary oxygen pressures such as that in air, it is difficult or impossible to demonstrate any sensitivity of the pupal heart to carbon monoxide. However, when the oxygen tension is decreased to very low levels, the heartbeat shows a clear sensitivity to carbon monoxide. Thus, at the low oxygen tension of 0.18% atm., the pupal heartbeat is inhibited 50 per cent by carbon monoxide at a pressure of only 5 mm. Hg.

7. Under these circumstances, the inhibition of the pupal heartbeat is light-reversible.

8. The actions of oxygen and carbon monoxide are considered in detail. The terminal oxidase of the pupal heart is found to be cytochrome oxidase.

9. The resistance of the pupal heart to carbon monoxide and to low oxygen pressures can be accounted for in terms of the presence in the pupal heart of a great excess of cytochrome oxidase relative to cytochrome c.