The Metabolism of Fertilized and Unfertilized Sea-Urchin Eggs

1. An investigation has been made into the effect of light and carbon monoxide on the respiration of sea-urchin eggs (Psammechinus miliaris), with special reference to unfertilized eggs. 2. The O2 uptake of unfertilized eggs in air is 38% higher in the dark than in light. This inhibitory action of light persists when gas mixtures containing CO and O2 are substituted for air. 3. Fertilized and unfertilized eggs differ in that the former's respiration is only about 10% inhibited by light. 4. In 80% CO in O2 in the dark, the O2 uptake of unfertilized eggs is 55% higher than in 80% N2 in O2 in the dark. In 95% CO in O2 in the dark, the O2 uptake of unfertilized eggs is only 7% higher than in 95% N2 in O2 in the dark, showing that at this partial pressure, CO exerts an inhibitory action on respiration. 5. There is no difference between O2 uptake in 80% CO in O2 in light and dark. O2 uptake in 95% CO in O2 in light is 45% higher than in this gas mixture in the dark, showing that at this partial pressure of CO, photo-reversal of respiratory inhibition occurs. 6. Results similar to those in 80% CO in O2 were obtained with gas mixtures containing lower partial pressures of CO. 7. Cytochromes a and b1 were identified spectroscopically in unfertilized eggs. 8. It is concluded that respiration is mediated through the cytochrome system before and after fertilization. In theories which postulate that cytochrome is ‘thrown into circulation’ at fertilization, the simultaneous light-inhibition of respiration, stimulation of O2 uptake by CO, and photo-reversible inhibition of O2 uptake by CO have not been taken into consideration.