The fourth ligand on the Zn(II) ion is a water molecule. The zinc coordination is tetrahedral. The three histidine residues are sometimes referred to as first coordination sphere ligands. This set of ligands is appropriate to give the water ligand the pKa of 6.5, a value where catalysis is most efficient.
Behind Closed Doors  is a country song written by Kenny O'Dell. It was first recorded by Charlie Rich for his 1973 album Behind Closed Doors. The single was Rich's first number-one hit on the country charts, spent 20 weeks on this chart, and was also a crossover hit on the pop charts. Background vocals were provided by The Nashville Edition.
Who sings the song black paper moon? Well if you're talking about the 2nd opening song in the anime Soul Eater, its by the group Tommy heavenly6 although the music video is weird... Was the song 'Black Velvet' about Elvis Presley? Yes, the song 'Black Velvet', by Allanah Myles was about Elvis Presley.