L-Cycloserine is a potent inhibitor of serine palmitoyl transferase (SPT), the first enzyme in the sphingolipid synthesis pathway.1 It inhibits bacterial SPT activity by 80% at a concentration of 25 ?M, which is 100 times more potent than D-cycloserine . L-Cycloserine inhibits SPT activity up to 86% in a dose-dependent manner in microsomes prepared from mouse brain following administration of doses ranging from 25-200 mg/kg. It also inhibits SPT in rabbit aorta and several aminotransferases in vitro and in vivo in rat.2,3 L-Cycloserine inhibits the growth of M. tuberculosis through branched chain aminotransferase inactivation, and it does so more rapidly and potently than D-cycloserine (MICs = 0.3 and 2.3 ?g/ml, respectively).4
1.Sundaram, K.S., and Lev, M.Inhibition of sphingolipid synthesis by cycloserine in vitro and in vivoJ. Neurochem.42(2)577-581(1984) 2.Williams, R.D., Sgoutas, D.S., Zaatari, G.S., et al.Inhibition of serine palmitoyltransferase activity in rabbit aorta by L-cycloserineJ. Lipid Res.28(12)1478-1481(1987) 3.Wong, D.T., Fuller, R.W., and Molloy, B.B.Inhibition of amino acid transaminases by L-cycloserineAdv. Enzyme Regul.11139-154(1973) 4.Amorim Franco, T.M., Favrot, L., Vergnolle, O., et al.Mechanism-based inhibition of the Mycobacterium tuberculosis branched-chain aminotransferase by D- and I-cycloserineACS Chem Biol.12(5)1235-1244(2017)