Electron transport components of <i>Heliobacterium chlorum</i> investigated by EPR spectroscopy at 9 and 35 GHz

Abstract

In membrane fragments of Heliobacterium chlorum we have observed by EPR spectroscopy the light‐induced reduction of a ferredoxin type electron acceptor with g y = 1.937 and g z = 1.879 at a midpoint potential E m &gt; −420 mV. A low‐potential ( E m &lt; −620 mV) electron acceptor at g = 2.0038 having a 15 G wide EPR line at 9.2 GHz and 18 G at 35 GHz could also be reduced by photoaccumulation; it is either located in the electron transport chain or on a side path. The linewidth of the primary donor P‐798 shows an anomalous temperature dependence, possibly caused by a change in dimeric structure induced by cooling. A scheme for the proposed electron transport chain is presented.