Principles of Fluorescence Spectroscopy

562 PROTEIN FLUORESCENCE
Figure 16.60. Structure of bovine adrenodoxin (top) and closeup views of W11 and W82 in the mutant proteins. Courtesy of Dr. Rita Bernhardt from
Saarlandes University, Germany.
Figure 16.61. Emission spectra and acrylamide Stern-Volmer plots
for adrenodoxin mutants F11W and Y82W. Revised from [163].
each step along the sequence (Figure 16.64). Hence,
residues from positions 94 to 105 are alternately exposed or
shielded from the solvent.
Figure 16.65 shows a summary of the tryptophan emission
maxima for about 150 mutants. Also indicated are
regions of α-helical and β-sheet structure. In β-sheet
regions the emission maxima oscillate with each step along
the sequence. For the α-helical region the emission maxima
oscillates with a periodicity of about 3.6 residues per cycle.
These data showed a close correlation between tryptophan
emission and the x-ray structures of lipocalin.
16.11. TRYPTOPHAN ANALOGUES
Advanced Topic
For calmodulin and other tyrosine-only proteins a genetically
inserted tryptophan residue can serve as a useful
probe. However, most proteins contain several tryptophan
residues that must all be removed to selectively observe the
inserted tryptophan. It is useful to have tryptophan analogues
that could be selectively observed in the presence of
tryptophan-containing proteins. This can be accomplished