School of Biological Sciences, Flinders University, GPO Box 2100, SA 5001.
Conserved residues among homologous proteins and the presence of two coordinated haems place strong constraints on the arrangement of the four proposed membrane helices in the cytochrome b subunit of the cytochrome bf complex in higher plant chloroplasts. With the addition of interconnecting loops we have modelled the complete protein within the membrane. The membrane was approximated by a continuous potential representing the hydrophobic effect. Various membrane thicknesses were modelled. The resulting position and orientation of the haems within the membrane was examined, with no strong evidence for cyt b563(L) being closer to the lumen side than b563(H) was to the stroma.