So the Aldol condensation reaction because this step is much more complicated than the simple hydrolysis step. So before we look at the reaction mechanism what actually takes place in the active side of the enzyme, let's discuss briefly this citrate synthase enzyme. So citrate synthase, the enzyme that catalyzes step one of the citric acid cycle is actually a dimer enzyme. It consists of two identical subunits and one of these subunits is shown on the board. Basically, we have two of these subunits that essentially interact with one another to form the citrate synthes. Now let's take a look at this subunit.