Protein densities from X-ray crystallographic coordinates

DENSITIES of the interiors of nine protein molecules were calculated using atomic coordinates obtained by X-ray crystallography. The resulting values, obtained for spherical regions of the molecules surrounding their centres of mass, are 10–25% below the apparent densities of the same molecules in solution. These regions include 20–50% of the total molecular mass. The densities calculated were 1.09–1.25 g cm−3 whereas the observed apparent solution densities of these proteins are 1.33–1.42 g cm−3.