The growth of hen egg-white lysozyme crystals over 28 days is followed by photographs, together with the accompanying concentration decrease in the supernatant. The concentration change is shown to be approximated by a theoretical curve derived from a set of simple differential equations. The concentration reaches a constant value after a few months, which is the solubility of the crystals. The solubility changes greatly with temperature, which reflects the enthalpy change upon crystallization. The length (L) and width (W) of a tetragonal crystal are also measured as a function of time. The change in L was greater than that of W, thus explaining the cause of the variation of the crystal morphology. These results, i.e. the kinetic equations, solubility diagrams, and morphogenesis, are examples of the rules underlying the growth of protein crystals.
