Crystal structure of the HSA-myristate-hemin complex (a) The protein secondary structure is shown schematically with the sub-domains colour-coded as follows: IA, red; IB – light red; IIA, green; IIB – light-green; IIIA, blue; IIIB – light blue; this colour scheme is maintained throughout. Ligands are shown in a space-filling representation, coloured by atom type: carbon – grey; nitrogen – blue; oxygen – red; iron – orange. Fatty acid binding sites are labelled 2–7. Except where stated otherwise, molecular graphics were prepared using Bobscript  and Raster3D . (b) An Fobs-Fcalc simulated annealing omit map  contoured at 2.5σ for hemin bound to subdomain IB. Selected amino acid sidechains are shown coloured by atom type. The dashed line indicates the two-fold symmetry axis that may relate alternative binding configurations of the porphyrin ring. The helix which overlies the bound hemin (residues 174–196) has been rendered semi-transparent.