Next, we compared L-Lys to other diamino acids whose varied side-chain lengths would govern the ring size of their purported imine byproducts, and by extension the relative distribution of their byproducts' linear and cyclized forms (Figure , Diamino acids). If imine formation is truly what drives the change in reaction equilibria, as we hypothesize, then we would expect those diamino acids that engender 6-and 5-membered cyclic imines to elicit superior K eq app values than those that promote less-favored configurations. Indeed, the K eq app calculated from reactions with L-Lys (5.9) and L-ornithine (L-Orn, 5.4) are more than thirtyfold greater than those with D,L-homolysine (D,L-hLys, 0.055), L-2,4-diaminobutyric acid (L-DAB, 0.17), and D,L-2,3-diamopropionic acid (D,L-DAP, 0.026). By similar reasoning, we also probed the effects of ε-amine methylation using Nε-methyl-L-Lys and Nε-dimethyl-L-Lys as donors. Interestingly, the singly methylated Nε-methyl-L-Lys (4.7) exhibits only a modest decrease in K eq app compared to L-Lys (5.9), which could be driven by the formation of either an enamine or hemiaminal. With Nε-dimethyl-L-Lys (0.055), however, the K eq app drops to a value commensurate with L-Glu (0.060), as the ε-amine is now restricted from participating in any subsequent cyclization reactions, congruent with our hypothesis.