EPR studies on cytochrome components in phosphorylating particles ofAzotobacter vinelandii

Abstract

Oxidized particles ofA. vinelandii show high-spin ferric signals with an axial and a rhombically distorted component with g-values at 5.94 and 6.24, 5.51, respectively. The signals behave similarly on variation of temperature and/or power and are, assigned to cytochromed. The addition of ligands such as cyanide and carbon monoxide to oxidized particles mainly affects the rhombic component of the signal in the g=6 region. Prolonged, incubation of cyanide with oxidized particles results in the appearance of two new low-spin ferric heme signals at g=2.99 and at g=3.23 which are tentatively assigned to low-spin forms of cyanide-liganded cytochromed. With computer signal-averaging of the EPR spectrum of oxidized particles, the presence of resonances in the g=3–4 region could be demonstrated. These resonances are assigned to cytochromeb1 (g-values at 3.68, 3.43),c-type cytochromes (g-values at 3.43, 3.25) and cytochromea1, and possibly a low-spin form of ac-type cytochrome (g-value at 3.03). These EPR results represent, to our knowledge, the only such studies reported on the membrane-boundb1 andc-type cytochromes of a bacterial respiratory-linked phosphorylating electron-transport chain.