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The nucleation of horse spleen ferritin (HSF) crystals on substrates was investigated using a new modification of the double pulse technique. The influence of three different structureless* substrates (glass, glass covered by methyl groups and poly-L-lysin template) on the nucleation was studied. The boundaries in the phase-diagram, which separate zones of crystal nucleation and growth were obtained by keeping pH = 5.0, and using CdSO4 as crystallizing agent. The steady-state nucleation rates were determined. The energy required for critical nuclei formation was evaluated (10-13 erg) and the sizes of critical nuclei were found (5 and 2 molecules).

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By using a supersaturation gradient along a protein solution contained in a glass capillary tube, we modified the classical double pulse technique, thus substantially accelerating the procedure of measurement of nucleation parameters. Data for the number of crystal nuclei, n vs nucleation time, t, were obtained for hen-egg-white lysozyme, chosen as a model because of the availability of reliable solubility data in the literature. The stationary nucleation rate and the nucleation time lag have been measured. Quantitative data for the work required for nucleus formation (Ak = 4.3x10-13 erg) and the size of the critical cluster (three molecules) were also obtained. Besides, it was observed that Ostwald ripening seems to play an important role for nucleation times longer than 150 min. Using the same technique, semi-quantitative investigations were performed with porcine pancreatic trypsin.
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