but also lysine and somewhat analogous cationic amino acids. Multiplication of known
transport systems is not the only change in the list of transport systems: in at least one case,
a presumably unique transport system, namely system XA, turns out to represent instead the
operation of system ASC 3 at low pH for anionic amino acids. The evidence that it can also
operate for dibasic amino acids makes it potentially a comprehensive system. 3 In contrast,
systems LI 4 and T, 5 which were for a time unrecognized and hence lumped with system L …