α-amylase crystal growth investigated by in situ atomic force microscopy

The growth behavior of porcine pancreatic cc-amylase at defined supersaturation has been investigated by means of temperature controlled in situ atomic force microscopy (AFM). The step velocities measured by AFM were in overall agreement with the normal growth rates of an individual face measured by optical microscopy. In addition, highly local growth dynamics could be visualized. Imaging in tapping mode revealed crystalline amylase aggregates attached to the basal face and their subsequent incorporation into growing terraces producing a macrodefect. At high supersaturation (beta = 1.6) 2-D nucleation was found to be the dominating growth mechanism, whereas at lower supersaturation (beta = 1.3) the growth process appears to be defect controlled (spiral growth). The analysis of step heights on 2-D nucleation islands (monomolecular protein layers) and growth steps (two molecules in height) in combination with results from light scattering experiments suggest that a single protein molecule is the basic growth unit. (C) 2001 Elsevier Science B,V, All rights reserved.