Growth kinetics of tetragonal lysozyme crystals

Abstract A method has been devised for immobilizing protein crystals in small volumes under defined conditions in order to determine growth rates on various faces. Using this method, we have investigated the growth kinetics of the [110] face of tetragonal hens egg white lysozyme crystals at varying degrees of bulk supersaturation. The growth rate data were analyzed using a simple convective-diffusive model to determine an empirical relationship between growth rate and local supersaturation at the interface. This empirical relationship describes the surface kinetics of the growth process, which together with the convective-diffusive model can be used to predict various details of the growth process as a function of crystal size, bulk supersaturation, and gravity level. It was shown that transport is dominated by convection in normal gravity for all crystal sizes larger than a few microns whereas transport is diffusion limited in a microgravity environment for sizes up to a few millimeters. Convection can become significant even in a microgravity environment for crystals approaching cm sizes. Growth of lysozyme will always be limited by surface kinetics in normal gravity because convective transport is sufficient to supply solute to the growth interface as fast as it can be incorporated into the lattice. In microgravity the transport can become sufficiently slow as the crystal becomes larger so that growth is limited by transport rather than surface kinetics. The implications of this are discussed.