The structure determination of membrane proteins is still a difficult task. Considering the fact that as many as 30% or more of cellular proteins are associated with the membrane (Arkin et al., 1997a), the paucity of high resolution structures of membrane proteins is in stark contrast to the number of soluble protein structures. Recent successes include cytochrome c oxidase Iwata et al 1995 S. Iwata, C. Ostermeier and H. Michel, Structure at 2.8 Å resolution of cytochrome c oxidase from paraoccus denitrificans, Nature 376 (1995), pp. 660–669. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (1485)(Iwata et al 1995) and (Tsukihara et al 1996), cytochrome bc 1 complex (Akiba et al., 1996) and the transmembrane part of the K+channel (Doyle et al., 1998). NMR and diffraction methods encounter numerous experimental obstacles due to the solubility problems of membrane proteins which normally require use of detergents. Other approaches use molecular modelling techniques combined with low resolution experimental data.