ISOLATION AND CHARACTERIZATION OF CYTOCHROME-D FROM TETRAHYMENA-PYRIFORMIS

Partially purified cytochrome d free of other cytochrome components has been isolated using detergent (Triton X-100) and salt (KCl). The isolated cytochrome d, has an absorption maximum at 615-617 nm and is capable of oxidizing the reduced cytochrome c553 of tetrahymena. Potentiometric titrations show that cytochrome d like cytochrome aa3 has a two-component structure with half-reduction potentials of 0.17 and 0.32 V. EPR studies of aerobic cytochrome d show low spin ferric heme resonances at g = 2.96 and g = 2.26 and a g = 2.0 signal characteristic of oxidized copper. EPR studies on oriented multilayers of partially purified cytochrome d show that the heme seen in the fully oxidized preparation is oriented in such a way that the angle between the heme normal and the membrane normal is approximately 90 °. © 1979.