Heme ci or cn of the Cytochrome b6f Complex, A Short Retrospective

The unexpected existence of heme ci (or cn) of cytochrome b6f complex was revealed to the scientific community in Spring 2003 at the Gordon Bioenergetics conference, taking place at Kimball Union Academy, NH, USA. The three-dimensional structures of the complex were published back-to-back by two independent groups in Fall 2003 (Kurisu et al. Science 302:1009–1014, 2003; Stroebel et al. Nature 426:413–418, 2003). Further information about the physico-chemical properties of this unusual heme was gathered in the following years. Here we shall re-examine early evidence for the presence of this unusual cytochrome, originally called G (Lavergne. Biochim Biophys Acta 725:25–33, 1983; Joliot and Joliot. Biochim Biophys Acta 933:319–333, 1988), which show the role that heme ci plays in electron transfer in the cytochrome b6f complex.