Principles of Fluorescence Spectroscopy

566 PROTEIN FLUORESCENCE
Figure 16.71. Amino-acid analogues inserted using a modified genetic
code. From [196–200].
320 nm so that intrinsic tryptophans do not interfere with
this probe. The mutant streptavidin with mchAla showed a
change in emission intensity upon binding biotin (Figure
16.73). Streptavidin was also synthesized with the anthracene-like
amino acid, yielding an unusual protein with the
emission of anthracene. It seems probable that these methods
for synthesis of labeled proteins will become more
widely used as the methodology becomes more available.
16.12. THE CHALLENGE OF
PROTEIN FLUORESCENCE
The intrinsic fluorescence of proteins represents a complex
spectroscopic challenge. At the initial level one has to deal
with multiple fluorophores with overlapping absorption and
emission spectra. The presence of multiple fluorophores is
itself a significant challenge. However, the actual situation
is still more complex. The dominant fluorophore tryptophan
displays complex spectral properties due to the presence of
two overlapping electronic states. It is now accepted that
Figure 16.72. Structures of streptavidin containing mchAla at position 120 or streptavidin with 2,6-dnsAF at position 44. From [199–200].