Observation of etch vigures on protein crystals by atomic force microscopy

Etch figures on the (I 10) face of lien egg white lysozyme crystals in aqueous solution were investigated by atomic force microscopy. Three types of etch pits with flat, "deep" flat and point bottoms were observed. All etch pits are elongated to the [-110] direction, similar to the growth of 2D islands. The etch pit density of contaminated crystals, fabricated from a widely used commercial sample, was approximately ten times greater than that of pure crystals. Moreover, the density of "deep" flat bottom pits on contaminated crystals increased with supersaturation, while their density on pure crystals remained almost constant. These results suggest that the impurity molecules incorporated during growth and the line defects, such as edge dislocations, induced by the molecules are the dominant defects in lysozyme crystals grown from commercially available samples.