Low-temperature electron paramagnetic resonance study of the ferricytochrome c-cardiolipin complex

Abstract
The electron paramagnetic resonance spectrum of the ferricytochrome c complex with cardiolipin was observed at temperatures below 20 K. For the low-spin iron(III) heme system complexed with the negatively charged lipid, the tetragonal and rhombic ligand field parameters (.DELTA./.lambda. = 3.58, V/.lambda. = 1.82) differ significantly from those (.DELTA./.lambda. = 2.53, V/.lambda. = 1.49) of the free ferricytochrome c sample. The g values of the complex (gx = 1.54 .+-. 0.02, gy= 2.26 .+-. 0.01, gz = 3.02 .+-. 0.01) are compared to the values for free ferricytochrome c (gx = 1.25 .+-. 0.02, gy = 2.25 .+-. 0.01, gz = 3.04 .+-. 0.01). Spectral alterations are interpreted in terms of the ligand field changes induced within the heme group by association with the negatively charged phosphoglyceride.