Electron Tunnelling in Cytochromes

OXIDATION of a c -type cytochrome by light absorbed by the photosynthetic system of the purple sulphur bacterium, Chromatium , at the temperature of liquid nitrogen was discovered by Chance and Nishimura 1 . Vredenberg and Duysens 2 made further measurements confirming that quantum efficiencies did not change by more than a factor of two, if that much, at the lowest temperatures. The light and instrument limitations on these measurements make any further conclusions about rates difficult.