Ultra-High Resolution X-Ray Diffraction From Crystals Of The Kinetic Mutant Of Human Carbonic Anhydrase Ii, His 64 Ala, And Its Complexes With Proton Acceptor Donors.

Crystals of human carbonic anhydrase II with a specific point mutation, His 64 to Ala, have been grown in a solution of ammonium sulfate in the presence of mercury chloride. The crystals appear in approximately two weeks and belong to the monoclinic space group P21, with unit cell parameters of a = 42.2 A, b = 41.4 A, c = 71.9 A , beta= 104.2 o and one carbonic anhydrase molecule in the asymmetric unit. The crystals diffract X-rays beyond 1.0 Å resolution. These crystals, soaked with exogenous proton acceptor donors, will be used in X-ray and neutron diffraction studies to map the fine water structure “proton wire” in the active site of carbonic anhydrase and to assign the intra- and intermolecular proton transfer pathway(s) from the zinc-bound water out to the bulk solvent.