Inhibition of Respiration and Photosynthesis in Chlorella Pyrenoidosa by Organic Com- Pounds That Inhibit Copper Catalysis*

The suggestion that compounds known to inhibit copper catalysis might exert an inhibiting effect upon photosynthesis and respiration in green plants arose primarily from the following considerations: (a) The aerobic oxidation of ascorbic acid is very sensitive to catalysis by copper-protein complexes in a great variety of plant press-juices (I). (b) Both copper (2) and ascorbic acid (3) are found in relatively high concentrations in green leaves and other plant tissues that have a capacity for photosynthesis. (c) Although the evidence is far from complete, it is not unreasonable to believe that copper and ascorbic acid may be concerned, directly or indirectly, with both respiration and photosynthesis in green plants. Previous work in other laboratories has shown that photosynthesis is more sensitive than respiration to inhibition by cyanide (4-6) and the urethanes (6, 7). The present investigation has shown that typical copper “poisons” inhibit both photosynthesis and respiration in Chlorella cells, the respiration being less sensitive than photosynthesis.