EPR spectroscopy of biological iron–sulfur clusters with spin-admixed S= 3/2

Abstract

The ground-state paramagnetism of synthetic cubane clusters, [Fe₄S₄L₄]^3-, can be of three types: pure spin, physical spin mixture, or spin-admixed. The former two types are also abundantly present in biology; a first biological example of the latter has recently been found in a ‘hybrid-cluster protein’. In this work the hybrid-cluster protein from Desulfovibriovulgaris, D. desulfuricans (wild type and Cys428Ser mutant), Escherichiacoli, and the Fe-hydrogenase from D. vulgaris have been studied to determine the EPR (with a main feature around g≈5) and ESEEM parameters, biological significance, and biological distribution of spin-admixed clusters.