To work, enzymes must first bind to a substrate molecule in their binding site. This initial reaction can be written as:

E + S <-> ES

where E is an enzyme, S is the substrate, and ES is the enzyme: substrate complex (effectively a single molecule). For a specific human enzyme, K = 4.1 * 10^9 at 37 C, with a forward rate constant of Kf = 1.2 * 10^8 1/M*s.

(a) Inserting mutations into the binding site of this enzyme caused a dramatic drop in the equilibrium constant of 3 orders of magnitude (Kmut = 3 * 10^6). However, the forward rate constant was found to be the same. Explain how this is possible.