The binding capacity of the L-leucine receptor from
Escherichia coli was measured with L-phenylalanine
and 4-fluoro-L-phenylalanine as substrates by fluorescence. The
apparent dissociation constants (KD)
for L-leucine, L-phenylalanine, and 4-fluoro-L-phenylalanine are
0.40, 0.18, and 0.26 respectively. 19F NMR data show
protein-induced shifts for the 4-fluoro-L-phenylalanine peak and
3-fluoro-L-phenylalanine when receptor is present. Evidence points
to the binding of only the L-isomers of these fluorine analogs.
