Structural Analysis and Aggregation Propensity of Reduced and Nonreduced Glycated Insulin Adducts Parnian Alavi & Reza Yousefi & Sara Amirghofran & Hamid Reza Karbalaei-Heidari & Ali Akbar Moosavi-Movahedi Received: 18 November 2012 / Accepted: 18 March 2013 / Published online: 14 April 2013 # Springer Science+Business Media New York 2013 Abstract The milieu within pancreatic β cells represents a favorable environment for glycation of insulin. Therefore, in this study, insulin samples were individually subjected to glycation under reducing and nonreducing conditions. As monitored by ortho- phthalaldehyde and fluorescamine assays, the reduced glycated insulin adduct demonstrates extensively higher level of glycation than the nonreduced glycated counterpart. Also, gel electrophoresis experiments suggest a significant impact of glycation under a reducing system on the level of insulin oligomerization. Furthermore, reduced and nonreduced glycated insulin adducts respectively exhibit full and partial resistance against dithiothreitol-induced aggregation. The results of thioflavin T and Congo red assays suggest the existence of a significant quantity of amyloid-like entities in the sample of reduced glycated insulin adduct. Both fluorescence and far-ultraviolet circular dichroism studies respectively suggest that the extents of unfolding and secondary structural alteration were closely correlated to the level of insulin glycation. Moreover, the surface tension of two glycated insulin adducts was inversely correlated to their glycation extents and to the quantity of exposed hydrophobic patches. Overall, the glucose-modified insulin molecules under reducing and nonreducing systems display different structural features having signif- icant consequences on aggregation behaviors and surface tension properties. The particular structural constraints of glycated insulin may reduce the binding interaction of this hormone to its receptor which is important for both insulin function and clearance. Keywords Insulin glycation . Structure . Oligomerization . Unfolding . Amyloid-like entity Appl Biochem Biotechnol (2013) 170:623–638 DOI 10.1007/s12010-013-0207-1 P. Alavi : R. Yousefi (*) : S. Amirghofran Protein Chemistry Laboratory (PCL), Department of Biology, College of Sciences, Shiraz University, Shiraz, Iran e-mail: ryousefi@shirazu.ac.ir H. R. Karbalaei-Heidari Molecular Biotechnology Laboratory (MBL), Department of Biology, College of Sciences, Shiraz University, Shiraz, Iran A. A. Moosavi-Movahedi Institute of Biochemistry and Biophysics (IBB), The University of Tehran, Tehran, Iran