Racemases and the aim of their study

Asymmetric but not stereoselective:
The racemases enzyme family catalyze the interconversion of both substrate enantiomers ^3.1. Although most enzymes are famous for being exquisitely asymmetric, by definition racemases process both enantiomers and have equilibrium constants equal to unity. So the question arises, how can these enzymes, which are inherently asymmetric, deal with both enantiomers with at least approximately equal facility? The logical answer to this question is that racemases must have evolved a functional and structural pseudosymmetry in their active sites.

Deprotonation of a high $pK_a$ hydrogen:
Another question, in this case not exclusive of racemases, is the rapid proton exchange involving carbon-hydrogen bond cleavage of carbon acids with relatively high $pK_a$. In the case of mandelic acid its $\alpha-$hydrogen has an estimated $pK_a$ in solution of $\sim$22 and $\sim$29 for its anion mandelate[213].

While in 0.40 M NaOD the $\alpha$-proton of sodium mandelate undergoes exchange very slowly even at 100$^o$C, in contrast, Mandelate Racemase provokes the same exchange reaction with a turnover number of $\sim$1000 $s^{-1}$ at 25$^o$C even at pH 7.5[214].^3.2This puzzling situation is a general problem that appears in many other enzymatic reactions, for example, triose-phosphate isomerase, $\Delta^5$-ketosteroid isomerase, citrate synthase, enolase, aconitase and fumarase[215].

Bearne and Wolfenden[216] published a work where the non-enzymatic mandelic racemization reaction is studied in the presence of many different acid-base catalysts at different concentrations and different pH. A comparison between the reaction kinetics of enzymatic and non-enzymatic processes has concluded that Mandelate Racemases produces a rate enhancement under neutral conditions at 25$^o$C of 1.7 10$^{15}$-fold.