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 microM INS/8.8 microM Zn2+ were exposed to 8 microM Cu2+ and 50 microM ascorbate for 90 min. The Cu2+ -catalyzed oxidation mainly targeted the B chain of INS, where the two histidine residues are located.