Observation of growth steps, spiral dislocations and molecular packing on the surface of lysozyme crystals with the atomic force microscope

The (110) faces of lysozyme crystals in their mother liquor have been investigated using an atomic force microscope (AFM) in height mode. Crystal growth and dissolution steps, as well as simultaneous growth and dissolution in pits, have been observed. Screw dislocations were also observed but the fine structure has not yet been investigated. Images that may possess molecular resolution were obtained and compared with theoretical images based on the crystallographic structure and the effects of arbitrary tip profiles. Crystallographic periodicities of 38 and 112 Å were observed. A recurring feature is a centered periodic array of minima that may be associated with one of the two nearly planar sheets of molecules present in the crystal that are parallel to the (110) faces.