In this paper, the aggregates in protein solution were investigated in order to study the change inside bulk solution that affect the amount and size of protein crystal after suffering thermal history effect. Two groups of lysozyme solution stored at 281 and 309 K separately were mixed with different ratio and precipitation agent was added. It was found that the amount of crystals decreased as the increase of the ratio of the heated solution, and the size of the growth units in solution increased at the same time. The situations of aggregates in lysozyme bulk solution stored at 281, 293 and 309 K separately were investigated by dynamic light scattering method for 5 weeks. The results showed that there always existed two separated aggregate groups in bulk solution. The group with smaller size was called units and that with the larger size was called clus-ters. The size of units kept almost constant as the stored time period increased. However, the size of clusters decreased to almost the same size as that of units after 5 weeks. The size decreasing rate of clusters was dependent on the storage temperature. Our results indicated that the homogeneity of protein solution in the induction time period and the mean size of units during nucleation process were affected by thermal history, which would finally affect the number of crystals grown.

Key words: thermal history effect, lysozyme, aggregate, light scattering