Abstract
1. The light-induced C14O2-fixing capacity of algal cells (Chlorella), as it was measured by the technique of Ca1vin et al. (2, 12), was found to be markedly decreased when quinone was added to the algal suspension.
2. The suppressing effect of quinone was reversible when its con-centration was low (10-4.3M or less), but became irreversible when the quinone concentration was raised (10-4M or more). The reversible suppression of C14O2-fixing capacity caused by quinone in lower con-centrations was explained as due to the reaction between the photo-chemically produced reducing substance and quinone, and the irreversibility of the quinone effect at its higher concentrations was inter-preted as being due to the irreversible destruction of the reaction system between the photochemically formed reducing substance and C14O2.
3. It was inferred that the Hill reaction brought about by quinone is nothing but a reaction between quinone and a reducing agent, whose photochemical formation in algal cells can be revealed by the measure-ment of light-induced C14O2-fixing capacity according to the method of Calvin et al.
This work was aided by grants from the Ministry of Education and the Rocke-feller Foundation. To these bodies we extend our grateful thanks. Our thanks are also due to Mr. Seikichi Izawa for help with some of the experiments.
