Studies with mechanism-based inactivators of lysine epsilon-transaminase from Achromobacter liquidum

Analogues of lysine containing a 4,5-acetylenic linkage (lysyne) or a cis- or trans-4,5-olefinic linkage (lysenes) function as substrates for a homogeneous L-lysine epsilon-transaminase from Achromobacter liquidum but partition between transamination and time-dependent inactivation. The partition ratio is lowest for lysyne (40 per inactivation event) and higher for trans-lysene (160 per inactivation event), and the cis-lysene transaminates 1600 times per inactivation event. cis-Lysene yields alpha-picolinate as a detectable accumulating product, presumably from cyclization of initial 6-aldehyde to dihydropicolinate and spontaneous autoxidation. The trans isomer also yields some picolinate as an identifiable product. The product from the few lysyne turnovers is as yet unknown but has strong absorbance at 318 nm. The inactive enzyme species from all three lysine analogues slowly (overnight) regain full activity after gel filtration chromatography and dialysis, suggesting reversal of the initial adduct-forming reaction. Initial studies with partially purified pseudomonad lysine alpha-racemase show alpha-3H incorporation from 3H2O but no inactivation consistent with the expectation that these lysine analogues could act readily as mechanism-based inactivators for pyridoxal P enzymes which act at the epsilon- but not the alpha-carbon of lysine.