Identification of L-amino acid/L-lysine alpha-amino oxidase in mouse brain

Lysine, an essential amino acid is catabolized in brain through only the pi pecolic acid pathway. During the formation of pipecolic acid, alpha-deamina tion of lysine, and the formation of the alpha-keto acid as well as its cyc lized product are pre-requisites. The enzyme mediated alpha-deamination of L-lysine and the formation of the alpha-keto acid and the cyclized product are not demonstrated so far. Both lysine and pipecolic acid are known to in crease in brain under the conditions of fasting, studies were therefore und ertaken to identify the enzyme responsible for the alpha-deamination of L-l ysine in the brain tissue of mice which were fasted. The detection of the a lpha-keto acid of L-lysine, alpha-keto-epsilon-amino caproic acid and its c yclized product, Delta(1)-piperidine-2-carboxylate was facilitated by the u se of L-[U-(14)-C]-lysine as the substrate. The quantitation of the radioac tivity in reaction products was done after separation by ion exchange chrom atographic methods. The formation of the alpha-keto acid was enzyme mediate d, the alpha-keto acid formed was established by reaction with N-methyl ben zothiazolinone hydrazone hydrochloride. The cyclized product was accounted in a fraction which matched the resolution of authentic pipecolic acid on t he Dowex column, and the cyclized product was confirmed by spectrophotometr y. The hitherto undemonstrated alpha-amino deaminating enzyme of L-lysine i n brain tissue, the alpha-keto acid of L-lysine and its cyclized product in a mammalian system could thus be demonstrated in the present study. These findings confirm the involvement of L-lysine oxidase/L-amino acid oxidase i n the formation of pipecolic acid from L-lysine.