Kinetics and equilibria of lysozyme precipitation and crystallization in concentrated ammonium sulfate solutions.
The kinetics and thermodynamics of lysozyme precipitation in ammonium sulfate solutions at pH 4 and 8 and room temperature were studied. X-ray powder diffraction (XRD) was used to characterize the structure of lysozyme precipitates. It was found that, if sufficient time was allowed, microcrystals developed following an induction period after initial lysozyme precipitation, even up to ionic strengths of 8 m and at acidic pH, where lysozyme is refractory to crystallization in ammonium sulfate. The full set of precipitation and crystallization data allowed construction of a phase diagram of lysozyme, showing the ammonium sulfate dependence. It suggests that precipitation may reflect a frustrated metastable liquid-liquid phase separation, which would allow this process to be understood within the framework of the generic phase diagram for proteins. The results also demonstrate that XRD, more frequently used for characterizing inorganic and organic polycrystalline materials, is useful both in characterizing the presence of crystals in the dense phase and in verifying the crystal form of proteins.
Department of Chemical Engineering, University of Delaware, Newark, 19716, USA.
Yu-Chia
YC
Cheng
Raul F
RF
Lobo
Stanley I
SI
Sandler
Abraham M
AM
Lenhoff
D000645:Ammonium Sulfate / Q000032:analysis / Q000737:chemistry*; D011232:Chemical Precipitation; D003460:Crystallization; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009113:Muramidase / Q000032:analysis / Q000737:chemistry*; D009994:Osmolar Concentration; D011208:Powders / Q000737:chemistry; D012996:Solutions; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
D011208:Powders; D012996:Solutions; D014867:Water; C421864:hen egg lysozyme; D009113:Muramidase; D000645:Ammonium Sulfate