| Abstract
| - The diffusion of a solute, fluorescein, into lysozyme protein crystals with different pore structureswas investigated. To determine the diffusion coefficients, three-dimensional solute concentration fieldsacquired by confocal laser scanning microscopy (CLSM) during diffusion into the crystals were comparedwith the output of a time-dependent 3-D diffusion model. The diffusion process was found to be anisotropic,and the degree of anisotropy increased in the order: triclinic, tetragonal and orthorhombic crystal morphology.A linear correlation between the pore diffusion coefficients and the pore sizes was established. The maximumsize of the solute, deduced from the established correlation of diffusion coefficients and pore size, was0.73 ± 0.06 nm, which was in the range of the average diameter of fluorescein (0.69 ± 0.02 nm). Thisproves that size exclusion is the key mechanism for solute diffusion in protein crystals. Hence, the originof solute diffusion anisotropy can be found in the packing of the protein molecules in the crystals, whichdetermines the crystal pore organization.
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