In this example the zinc ion acts a generalized acid and stabilizes the developing O- as water attacks the carbonyl. Zinc can also perform a different role in enzymes like the role it performs in carbonic anhydrase. Here the metal binds H2O and makes it acidic enough to lose a proton and form a Zn-OH group. The zinc metal serves as a nucleophile to the substrate. A four-subunit molecule, containing a iron atom in each subunit, in which each subunit binds a single molecule of oxygen.
Hemoglobin transports oxygen from the lungs to the capillaries of the tissue.
Cytochromes Cytochromes are integral membrane proteins. Cytochromes contain iron which serves to carry electrons between two segments of the electron-transport chain. The iron is reversibly oxidizable and serves as the actual electron acceptor for the cytochrome. Alcohol Dehydrogenase A zinc metalloenzyme with broad specificity. An electron transferring proteins involved in one-electron transfer processes.