Nuclear magnetic resonance studies of carbonic anhydrase catalyzed reversible hydration of acetaldehyde by the saturation transfer method.

The catalysis of the chemical exchange between acetaldehyde and its hydrate by bovine carbonic anhydrase B was investigated by the NMR line broadening and saturation transfer techniques. While both chemical exchange and binding to the enzyme had an effect on the line broadening of acetaldehyde and its hydrate, the saturation transfer method enabled us to measure the exchange without the interference from the effect of the binding. p-Toluenesulfonamide and azide ion were found to inhibit completely the carbonic anhydrase catalyzed exchange reaction. However, there was a residual line broadening of the acetaldehyde by the enzyme in their presence. This was interpreted as binding to sites other than the active site of the enzyme. The pH profile of the catalysis of the reversible hydration of acetaldehyde by carbonic anhydrase in the absence of a buffer indicates high- and low-activity forms of the enzyme with a transition at pD 7.65. The cadmium(II) enzyme was found to be inactive, and the cobalt(II) derivative was found to have similar activity to that of the native system.