Interaction of lead ions with bovine carbonic anhydrase

The interaction of lead (Pb2+) ions with apocarbonic anhydrase is studied by u.v. difference spectroscopy. The Pb2+ results are compared with those of Zn2+ interacting with apocarbonic anhydrase. The results of both metals interacting with apoenzyme are related to the difference spectra of Pb2+ and Zn2+ with Trp and Tyr model compounds. The interaction of Pb2+ with apocarbonic anhydrase containing an acetylated tyrosine residue is examined. Evidence is presented that Pb2+ is located in the active site cavity of apocarbonic anhydrase, but displaced from the zinc His ligands, interacting with Tyr 7. An attempt is made to rationalize the metal-chromophore micro-environment based on analysis of the 270-295 nm u.v. region of the difference spectra.