Studies on an Active Site residue, E177, That Affects Binding of the Coenzyme in D-Amino Acid Transaminase, and Mechanistic Studies on a Suicide Substrate

While the E177S mutation in D-amino acid transaminase has a reduced ability to transaminate D-alanine, the efficiency of β-elimination of β-chloro-D-alanine remains almost intact. Interestingly, the latter reaction showed the appearance of an intermediate absorbing around 460 nm with this attenuated enzyme. The protein CD spectrum of the apo-enzyme of E177S resembled that of wild-type enzyme, but that of E 177K showed a negative elipticity around 280 nm.