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.
.youtube_sc iframe.yp{display:none;}. Since then the track has been covered in 1995 by Alan Jackson and by Kellie Pickler in 2008. The song recently experienced a resurgence in popularity after being performed on The Voice UK talent show by the young British country music singer Mike Ward. On The Voice UK 2013 Ward sang âDonât Close Your Eyesâ during the blind auditions, then again in the live final where he finished in the top 3 but failed to win.