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. So we have historine residue one, two, and three, and they're bound to the zinc, as shown. And the final group is a water molecule. And this is the same water molecule that will react with the carbon dioxide to ultimately produce the bicarbonate.