title: Low-temperature EPR and Mössbauer spectroscopy of two cytochromes with His-Met axial coordination exhibiting HALS signals.
abstract: C-type cytochromes with histidine-methionine (His-Met) iron coordination play important roles in electron-transfer reactions and in enzymes. Low-temperature electron paramagnetic resonance (EPR) spectra of low-spin ferric cytochromes c can be divided into two groups, depending on the spread of g values: the normal rhombic ones with small g anisotropy and g(max) below 3.2, and those featuring large g anisotropy with g(max) between 3.3 and 3.8, also denoted as highly axial low spin (HALS) species. Herein we present the detailed magnetic properties of cytochrome c(553) from Bacillus pasteurii (g(max) 3.36) and cytochrome c(552) from Nitrosomonas europaea (g(max) 3.34) over the pH range 6.2 to 8.2. Besides being structurally very similar, cytochrome c(553) shows the presence of a minor rhombic species at pH 6.2 (6 %), whereas cytochrome c(552) has about 25 % rhombic species over pH 7.5. The detailed Mössbauer analysis of cytochrome c(552) confirms the presence of these two low-spin ferric species (HALS and rhombic) together with an 8 % ferrous form with parameters comparable to the horse cytochrome c. Both EPR and Mössbauer data of axial cytochromes c with His-Met iron coordination are consistent with an electronic (d(xy))(2) (d(xz))(2) (d(yz))(1) ground state, which is typical for Type I model hemes.
authors: Department of Molecular Biosciences, University of Oslo, Box 1041 Blindern, 0316 Oslo, Norway.
authors: Giorgio
authors: G
authors: Zoppellaro
authors: Thomas
authors: T
authors: Teschner
authors: Espen
authors: E
authors: Harbitz
authors: Volker
authors: V
authors: Schünemann
authors: Solveig
authors: S
authors: Karlsen
authors: David M
authors: DM
authors: Arciero
authors: Stefano
authors: S
authors: Ciurli
authors: Alfred X
authors: AX
authors: Trautwein
authors: Alan B
authors: AB
authors: Hooper
authors: K Kristoffer
authors: KK
authors: Andersson