An electron spin resonance study of high spin forms of cobalt(II) bovine carbonic anhydrase

The ESR spectra of bovine Co(II) carbonic anhydrase at 7 K at low and high pH and of the iodide derivative have been analyzed. The spectrum of the low pH form shows axial symmetry whilst that at high pH is rhombically distorted. This anisotropy is still more accentuated in the iodide derivative. The high pH (hydroxyl) form and the iodide derivative are thought to have a tetracoordinate trigonal pyramidal structure, with a fifth more distant axial ligand. The low pH form is consistent with a pseudotetrahedral geometry previously postulated.