Carbon dioxide hydration activity and metal—substrate distances of manganese (II) human carbonic anhydrase B determined by 13C magnetization—transfer NMR

A CO 2hydration activity for Mn(II) human carbonic anhydrase B (MnHCAB) of 7% of the activity of the native Zn 2+enzyme has been determined using a 13C magnetization—transfer NMR approach, that involves two complementary experiments. As this approach also allows a determination of the individual relaxation rates of the enzyme-bound CO 2and HCO −3, an evaluation could be made of the distances between these substrates and the paramagnetic Mn 2+in the active site. Thus HCO −3is found to bind directly to Mn 2+, whereas CO 2is attached relatively weakly to the enzyme without a direct bond to the metal ion.