Question

Cobalt(II) can substitute for Zn(II) in carbonic anhydrase and other proteins in which the metal ion acts as a Lewis Acid. The coordination chemistry of Co2+ is very similar to that of Zn2+, and the two ions have almost identical radii. Cobalt ion is an excellent structural and functional model for studies of a protein’s zinc binding sites. The advantage of Co(II)–substituted proteins is that they exhibit d → d transitions in the visible region of the electromagnetic spectrum, as well as charge transfer transitions in the UV region, while Zn(II) complexes are spectroscopically “silent.” a. Compare the role of Co in carbonic anhydrase to that in methionine synthase. b. Which redox state(s) of Co are catalytically active in these two proteins? c. Draw the reaction cycles of these two proteins focusing on the metal ion. Show the redox state of the metal ion in all intermediates.

Answer 1