In turn, the secreted citrulline is taken up by T-ALL blasts, which, subsequently, convert it into argininosuccinate and, eventually, into Arg trough the activity of Argininosuccinate Synthetase (ASS) and Argininosuccinate Lyase (ASL) (Sugimura et al., 1990). This evidence concerns the gene ASS1 and acute lymphoblastic leukemia.