Crystal growth of calcite mediated by ovalbumin and lysozyme: Atomic force microscopy study

Ovalbumin and lysozyme are two major egg white proteins and putatively related to the formation of the mammillary layer of eggshells. In this work, we have investigated their influences on the morphology and growth kinetics of hillocks at the molecular scale using fluid-cell atomic force microscopy. Our studies identified two roles for ovalbumin, favoring the formation of amorphous calcium carbonate-protein clusters on terrace surface and accelerating the step growth kinetics via reduction of the energy barrier for ion attachment to crystal steps. The two effects are intimately linked to the inherent characteristics of ovalbumin, i.e., being acidic and amphiphilic. In contrast, lysozyme as a basic protein did not induce the formation of any moldable transient phases. Instead, it interacted with step edges and pinned them, leading to step bunching and even step advancement stop at higher concentrations. These roles and their associated interactions on the molecular scale are related to the macroscopic features of eggshells and provide a reliable basis for further investigation into their influences in more complex systems mimicking native biological environment. © 2013 American Chemical Society.