In this case, water is also not a strong enough nucleophile to actually attack the carbon of this double bond. And so what must take place is again, we see that the histidine actually takes away the H from this oxygen and that transforms the water into a hydroxyl. And the hydroxide is a good enough nucleophile. So remember from organic chemistry that hydroxide molecules contain a full negative charge on the oxygen. And so that makes it a strong nuclear file. And so this nitrogen takes away the H atom.