And anytime any biological system uses a zinc atom in nature, the zinc atom always contains an oxidation state of positive two. So it has a net charge of positive two. And what that means is we have four different groups which are bound to that zinc atom. So this is a zinc atom. It has a charge of positive two, and it is bound to four different groups. Now, three of these groups are these ring structures that are part of the side chains of histetine residue.