NEUTRON-DIFFRACTION ANALYSIS OF THE SOLVENT ACCESSIBLE VOLUME IN CUBIC INSULIN CRYSTALS

The average-contact distance between protein and solvent surface atoms in cubic insulin crystals has been determined from two sets of 15 Ang strom resolution neutron diffraction data. A contact distance between the water hydrogen sites and the protein surface that is significantly shorter than the average protein-water oxygen contact distance implie s that many water molecules are oriented with hydrogen atoms pointed t owards the protein surface. The shape of the protein solvent interface is consistent with the protein envelope obtained from atomic co-ordin ates.