Protein crystals diffusion times

Steinhoff et al. (1989) measured the temperature and hydration dependence of the ESR spectra of hemoglobin spin-labeled at cysteine )8-93. They observed the critical temperature near 200 K, as described above, and the sensitivity of the spectrum to hydration level. Spectrum simulations suggested that there were two types of motion in the dry protein, a fast vibration of the label within a limited motion cone upon the addition of water, a hydration-dependent motion assigned to the fluctuations of the protein, of correlation time 10 sec in samples of high hydration and at 300 K. The temperature dependence of the motional properties of a spin probe (TEMPONE), diffused into hydrated single crystals, closely paralleled the motional properties of the label. This was taken to be evidence for coupling between the dynamical properties of the protein and the adjacent solvent. 

Some diffusion times for molecules into protein crystal... 

Protein crystals commonly contain 40-50 per cent water by weight, sometimes more, and there is much evidence to indicate that the conformation of the protein in the crystal is in general extremely close to that in solution. Hence the crystal studies provide relevant evidence regarding water-protein interactions in dilute solutions. The diffraction patterns obtained require exposures of many hours hence the structures calculated from them represent averaged positions for the atoms and molecules in the structure. Water molecules, in bulk water, at room temperature, have rotational relaxation times of the order of 10" s (lOps). The linear diffusion coefficient of water is near 2 x 10"° cm2 C", so the root mean square linear displacement of a water molecule in lOps would be of the order of 4-5 8. 

Crystallization experiments carried out on hen egg white lysozyme (HEWL) demonstrated that, under comparable or even lower supersaturation ratio, induction times for protein crystals grown on polypropylene membranes are lower than those reported in literature for conventional vapor diffusion techniques (Di Proflo et al. 

Purified MeHNL was crystallized by the sitting-drop vapor-diffusion method. The 10-20 mm bipyramidal crystals formed were cross-linked with glutaraldehyde and used as biocatalyst for the synthesis of optically active cyanohydrins. The cross-linked crystals were more stable than Celite-immobilized enzymes when incubated in organic solvents, especially in polar solvents. After six consecutive batch reactions in dibutyl ether, the remaining activity of the cross-linked crystals was more than 70 times higher than for the immobilized enzymes. Nevertheless, the specific activity of the cross-linked crystals per milligram protein was reduced compared with the activity of Celite-immobilized enzymes [53],... 

---