THE CYTOCHROME SYSTEM IN MARINE LAMELLIBRANCH TISSUES

¹ Department of Zoology, University of Kyoto, Kyoto, Japan

1. The cytochrome system of the lamellibranchs, Crassostrea gigas, Pinctada martensii and Mytilus crassitesta, has been studied in relation to the respiration of intact tissues.

2. The visceral cells possess a normal cytochrome system consisting of cytochromes a, b, c, and a₃, i.e., cytochrome oxidase. The oxidase is strongly inhibited by cyanide and carbon monoxide. The carbon monoxide inhibition of the enzyme is completely eliminated by light.

3. Cytochromes are most plentiful in the heart, where cytochrome c is predominant or equal to b, while b is apparently more predominant than a + a₃ or c in other tissues.

4. In a gas mixture of 90% CO and 10% O₂, the respiration of various tissues is inhibited by about 50% in the dark and the inhibition is completely eliminated by the illumination. Cyanide, 0.001 M, depresses the respiration of the oyster tissues to about 15-20% of the control, and the inhibition is partly reversed in the presence of methylene blue (6 x 10^-5 M) nearly saturated in sea water.

5. It is concluded that about 80% or more of the total respiration of intact lamellibranch tissues proceeds through the cytochrome system.