Lysinoalanine as a lysine antagonist: incorporation into protein as a possible mechanism of toxicity

Lysinoalanine [N^ε-(DL-2-amino-2-carboxyethyl)-L-lysine; LAL] is a nephrotoxic lysine analog formed in proteins as a result of alkali and/or heat treatment. Lysinoalanine induces alterations in the renal epithelial cells of the pars recta region of the proximal tubules (Woodard and Alvarez, 1967; Woodard and Short, 1973). This lesion was first observed by Woodard and Alvarez (1967) and designated as nephrocytomegalia by Woodard and Short (1973).

Lysinoalanine was shown to be a competitve inhibitor of lysyl-tRNA-synthetase (EC 6.1.1.6) from prokaryotic and eukaryotic cells in vitro when present at micromolar concentrations. The apparent K_i for lysinoalanine for E. coli lysyl-tRNA-synthetase was 9.4 x 10^-5 M and for rabbit liver lysyl-tRNA-synthetase was 1.5 X 10^-4 M. The apparent K_m for the esterification of E. coli and rabbit liver tRNAs was 2.0 x 10^-5 M and 5.0 x 10^-5 M, respectively.

Lysinoalanine inhibited the incorporation of ¹⁴C-lysine into protein by a cell-free eukaryotic protein synthesizing system. Inhibition was 69.7% and 18.4% at lysinoalanine concentrations of 1.0 mM and 0.1 mM, respectively.

¹⁴C-Lysinoalanine was incorporated into protein by a cell-free eukaryotic protein synthesizing system when present at micromolar concentrations as evidenced by the formation of hot TCA precipitable radioactivity and fluorography of a dried polyacrylamide gel. The proteins labeled with lysinoalanine coelectrophoresed with those labeled with lysine. These results indicate that lysinoalanine is an inhibitor of both prokaryotic and eukaryotic lysyl-tRNA-synthetase at concentrations which might occur in vivo. These observations and a possible mechanism of lysinoalanine-induced nephrocytomegalia are presented.