We find this observation of interest, as such conformational enrichment of productive substrate poses has been observed in several natural and engineered enzymes. At a minimum, it has been observed in two other series of Kemp eliminases: the HG3 series 47 mentioned above, and the KE07 series. We have further observed such enrichment in the transition of chalcone isomerases from a solute binding protein to enzymes, where the emergence of enzymatic activity on this scaffold is correlated with a 180° flip of the substrate from a non-productive conformation in the ancestor to a productive conformation in the extant enzyme. Further, conformational selection of the active site (not substrate) has been observed during the evolution of a phosphotriesterase to an arylesterase in a phosphotriesterase from Pseudomonas diminuta. Substrate flipping has also been observed during the engineering of a selective halohydrin dehydrogenase, in this case impacting enzyme selectivity. Our data adds to this body of literature, suggesting it is not an obscure phenomenon.