Synthesis of neuroactive guanidino compounds by rat kidney L-arginine: glycine amidinotransferase.

Several neuroactive guanidino compounds have been reported to be synthesized in mammals by transamidination reactions. The enzyme(s) responsible for their synthesis and their location in the body has not been well established. The purpose of this investigation was to determine if purified homogeneous rat kidney alpha- and beta-L-arginine : glycine amidinotransferase (transamidinase) would catalyze the synthesis of certain neuroactive guanidino compounds, and if so, to determine if any catalytic specificity existed between the two forms of the enzymes. L-Arginine (Arg) was used as the amidino group donor and the following compounds were investigated for their ability to accept the amidino group: ethanolamine; 4-aminobutyric acid; lysine; 5-aminovaleric acid; 3-aminopropionic acid; taurine; L-glutamic acid (Glu); L-aspartic acid (Asp); and histidine (His). All of the above listed compounds served as amidino group acceptors for the enzyme except Glu, Asp and His. No differences were found between the alpha- and beta-transamidinase in any of the experiments reported, and the synthesis of 2-guanidinoethanol by the enzyme was by a sequential mechanism with a Km for Arg and ethanolamine of 14mM and 163mM, respectively. The possibility that the site of synthesis of the neuroactive guanidino compounds in the kidney and perhaps pancreas is discussed.