PRECRYSTALLIZATION AGGREGATION OF INSULIN BY DYNAMIC LIGHT-SCATTERING AND COMPARISON WITH CANAVALIN

The aggregation of insulin prior to crystallization as a rhombohedral crystal of the 2Zn-insulin hexamer was studied by dynamic light scattering (DLS) using photon correlation spectroscopy (PCS). Results indicate that the 2Zn-insulin hexamer does not aggregate into higher oligomers in solution prior to crystallization. It is, therefore, suggested that the hexamer is the crystallizing species, strongly implying that the crystal grows by addition of hexamers to the crystal. This behavior is discussed in terms of the high and specific affinity of zinc coordination to insulin and is compared to the aggregation behavior (measured by DLS-PCS) of the oligomeric protein canavalin prior to crystallization.