Interactions between ferredoxin and chlorophyll in a monolayer system.

Ferredoxin (Fd) is surface active; both its area/molecule, A, and surface potential, AV, (at an air-water interface) vary with the pH of the subphase. From the surface isotherms (at pH 7.7) A and AV are 167 Ä2 and 170 + 20mV, respectively, when the surface tension is 10 dyne/cm. Fd and chlorophyll a (Chi) appear to form a mixed monomolecular film. At pH 7.7 a maximum interaction between Fd and Chi is observed when the monolayer contains a mole ratio of Fd/Chl ^ 2. Irradiaion of Chl-Fd films, in nitrogen atmosphere, results in a bleaching of Chi and an increase of A V. The quantum yield for this bleaching is estimated to be 0.4.