title: Multimerization and aggregation of native-state insulin: effect of zinc.
abstract: The aggregation of insulin is complicated by the coexistence of various multimers, especially in the presence of Zn(2+). Most investigations of insulin multimerization tend to overlook aggregation kinetics, while studies of insulin aggregation generally pay little attention to multimerization. A clear understanding of the starting multimer state of insulin is necessary for the elucidation of its aggregation mechanism. In this work, the native-state aggregation of insulin as either the Zn-insulin hexamer or the Zn-free dimer was studied by turbidimetry and dynamic light scattering, at low ionic strength and pH near pI. The two states were achieved by varying the Zn(2+) content of insulin at low concentrations, in accordance with size-exclusion chromatography results and literature findings (Tantipolphan, R.; Romeijn, S.; Engelsman, J. d.; Torosantucci, R.; Rasmussen, T.; Jiskoot, W. J. Pharm. Biomed. 2010, 52, 195). The much greater aggregation rate and limiting turbidity (τ(∞)) for the Zn-insulin hexamer relative to the Zn-free dimer was explained by their different aggregation mechanisms. Sequential first-order kinetic regimes and the concentration dependence of τ(∞) for the Zn-insulin hexamer indicate a nucleation and growth mechanism, as proposed by Wang and Kurganov (Wang, K.; Kurganov, B. I. Biophys. Chem. 2003, 106, 97). The pure second-order process for the Zn-free dimer suggests isodesmic aggregation, consistent with the literature. The aggregation behavior at an intermediate Zn(2+) concentration appears to be the sum of the two processes.
authors: Department of Chemistry, University of Massachusetts, 710 North Pleasant Street, Amherst, Massachusetts 01003, United States.
authors: Yisheng
authors: Y
authors: Xu
authors: Yunfeng
authors: Y
authors: Yan
authors: Daniel
authors: D
authors: Seeman
authors: Lianhong
authors: L
authors: Sun
authors: Paul L
authors: PL
authors: Dubin
mesh_terms: D002850:Chromatography, Gel; D007328:Insulin / Q000737:chemistry*; D009391:Nephelometry and Turbidimetry; D011108:Polymers / Q000737:chemistry*; D015032:Zinc / Q000737:chemistry*
chemical_list: D007328:Insulin; D011108:Polymers; D015032:Zinc