The kinetics of the reaction of Octopus vulgaris hemocyanin with cyanide. Its significance for the structure of the 11 S subunit of molluscan hemocyanin.

Native Octopus vulgaris hemocyanin (Hc) reacts with cyanide stepwise. The first step involves the formation of a complex HcCN with O2 displacement. This complex reacts further with cyanide causing the removal of one copper ion from the active site. The same reaction sequence occurs for the extraction of the second metal ion. The formation of the HcCN complex and the removal of the first and the second copper ion can be differentiated according to the KCN concentration. The rate of metal removal is slightly affected by KCN concentration. The kinetics are dominated by site-site interactions. The kinetic curves show only slight differences when the protein is in the 11 S or 49 S aggregation states, suggesting that the site-site interactions are restricted mainly within the 11 S structure. A kinetic model describing the removal of the first copper ion is proposed assuming that the 11 S component (MW 250,000) is an annular-shaped structure made by five equivalent functional subunits (MW 50,000). An explanation for the incomplete copper removal from molluscan Hc is given. The results are compared with those previously reported for Carcinus maenas Hc.