The release of this ion from the N-lobe of a protein that binds to it is mediated by a pair of hydrogen bonded lysines called the "dilysine trigger." After pH is lowered to about 5.4, this [emphasize] insoluble ion dissociates from a complex and is converted into a soluble counterpart by STEAP3. It has nothing to do with cyanide poisoning, but methylene blue reacts with this ion to treat a condition that often manifests as blue skin. Since this ion is present in (*) [emphasize] aerobic (-5[1])environments, bacteria secrete enterobactin and other siderophores that scavenge this ion (-5[2])by binding to it with high affinity. (10[1])Two species of this ion bind to transferrin with an association constant of 10 to the negative 22nd. The adjective "ferric" (-5[1])refers to, for 10 points, what metal cation, (0[1]-5[1])a more oxidized form of the ion found at the center of hemoglobin? ■END■ (10[4]0[1])