Mechanism of Inactivation of GABA Aminotransferase by (<i>E</i>)- and (<i>Z</i>)‑(1<i>S</i>,3<i>S</i>)‑3-Amino-4-fluoromethylenyl-1-cyclopentanoic Acid

When γ-aminobutyric acid (GABA), the major inhibitory neurotransmitter in the mammalian central nervous system, falls below a threshold level, seizures occur. One approach to raise GABA concentrations is to inhibit GABA aminotransferase (GABA-AT), a pyridoxal 5′-phosphate-dependent enzyme that degrades GABA. We have previously developed (1<i>S</i>,3<i>S</i>)-3-amino-4-difluoromethylene-1-cyclopentanoic acid (CPP-115), which is 186 times more efficient in inactivating GABA-AT than vigabatrin, the only FDA-approved inactivator of GABA-AT. We also developed (<i>E</i>)- and (<i>Z</i>)-(1<i>S</i>,3<i>S</i>)-3-amino-4-fluoromethylenyl-1-cyclopentanoic acid (<b>1</b> and <b>2</b>, respectively), monofluorinated analogs of CPP-115, which are comparable to vigabatrin in inactivating GABA-AT. Here, we report the mechanism of inactivation of GABA-AT by <b>1</b> and <b>2</b>. Both produce a metabolite that induces disruption of the Glu270–Arg445 salt bridge to accommodate interaction between the metabolite formyl group and Arg445. This is the second time that Arg445 has interacted with a ligand and is involved in GABA-AT inactivation, thereby confirming the importance of Arg445 in future inactivator design.