Selective oxidation of Zn2+-insulin catalyzed by Cu2+

The purpose of this study is to quantitate the sensitivity of Zn2+‐insulin to oxidation catalyzed by various redox active transition metals, Cu2+, Fe2+, Mn2+, Ni2+, Co2+, Cr3+. Human recombinant insulin (INS) was subjected to oxidation under various conditions in the presence and absence of Zn2+ and ascorbate. The extent of oxidation was monitored by RP‐HPLC. Only Cu2+, but none of the other metals or combination thereof, for example, Ni2+/Co2+, Co2+/Cr3+, and Ni2+/Cr3+, catalyzed INS oxidation, for example, to an extent of 45% when 20 µM INS/8.8 µM Zn2+ were exposed to 8 µM Cu2+ and 50 µM ascorbate for 90 min. The Cu2+‐catalyzed oxidation mainly targeted the B chain of INS, where the two histidine residues are located. © 2007 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 96: 1844-1847, 2007