Cytochrome c-554 from Methylosinus trichosporium OB3b; a Protein That Belongs to the Cytochrome c2 Family and Exhibits a HALS-Type EPR Signal

摘要

A small soluble cytochrome c-554 purified from Methylosinus trichosporium OB3b has been purified and analyzed by amino acid sequencing, mass spectrometry, visible, CD and EPR spectroscopies. It is found to be a mono heme protein with a characteristic cytochrome c fold, thus fitting into the class of cytochrome c 2, which is the bacterial homologue of mitochondrial cytochrome c. The heme iron has a Histidine/Methionine axial ligation and exhibits a highly anisotropic/axial low spin (HALS) EPR signal, with a g max at 3.40, and ligand field parameters V/ξ  = 0.99, Δ/ξ  = 4.57. This gives the rhombicity V/Δ  = 0.22. The structural basis for this HALS EPR signal in Histidine/Methionine ligated hemes is not resolved. The ligand field parameters observed for cytochrome c-554 fits the observed pattern for other cytochromes with similar ligation and EPR behaviour.