Arg-Strain
#1 is the only strain with a specific requirement
for
a specific amino acid, in this case
arg. Therefore, arg
must be the last amino acid synthesized in the pathway. The
conversion
of Y to
arg is under control of the last
enzyme in the pathway,
C.
Addition of either X or Y cannot produce growth,
because
although
X can be converted to Y, in the absence of a functional
enzyme C, Y cannot be converted to
Z (arg).
