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.
P.J.'s Yellow Ledbetter...maybe Hubbie's muse from his song Yellow Gal died unexpectedly/young, as a Vedder friend or gal may have...Hubbie Ledbetter(The famous Leadbelly) didn't write the Death Letter Blues, but he sure sang 'em/it...the lyrics from a late version of Death Letter Blues(sung by Jerry Garcia at a Dead concert in the late 60's) have many similarities to the Pearl Jam lyrics...even the original Son House lyrics for Death Letter Blues have much in common...I'm not saying ...