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.
The song was sung and recorded by Billie Holiday many times, from the mid-1930s onwards. It was sung by Irene Dunne in the movie A Guy Named Joe with Spencer Tracy (MGM, 1943).The song was revived to even greater success in 1944, when the 1940 recording by Harry James (Dick Haymes vocal) was re-released (during the 1942â44 musicians' strike, which prevented recording of new material) (Billboard #1).ack Jones for his 1965 album Dear Heart, Al Hirt on his 1965 album They're Playing Our Song, and Sun Ra in 1973 and 1977 in his posthumous album Some Blues But Not The Kind That's Blue. A version was also recorded by Ben Bernie And His Orchestra, which was featured at the end of the Woody Allen film Zelig.