Fluorescence Technologies for Monitoring Interactions Between Biological Molecules In Vitro - Progress in Molecular Biology and Translational Science - page 113

Blue shift Red shift

Quantum
yield

Ex Em

Wavelength (nm)

Figure 4.3 Hypsochromic (blue) or bathochromic (red) shift with quantum yield
increase.

other amphiphilic molecules generally induces changes in the environment,
providing information on the surrounding of tryptophan and thereby of
proteins. 10 If a globular protein containing several tryptophans in its
“hydrophobic” core is denatured, the environment of tryptophans is
modified and a shift of the emission spectrum maximum to a longer
wavelength (bathochromic/red shift) is observed. This effect arises from
the exposure of tryptophan to an aqueous environment as opposed to a
hydrophobic protein core. In contrast, the addition of a surfactant such as
phospholipid vesicles to a protein that contains a tryptophan exposed to
the aqueous solvent will induce a shift of the emission spectrum maximum
to a shorter wavelength (hypsochromic/blue shift) if the tryptophan
becomes embedded in the phospholipid vesicle. Thus the transfer of
tryptophan residues from a polar to a less polar environment such as the
membrane bilayer is usually associated with a blue shift. In addition, this
blue shift may be accompanied by an increase in the quantum yield of
tryptophan ( Fig. 4.3 ).
An alternative approach to the intrinsic fluorescence of tryptophan is the
covalent attachment of an extrinsic fluorophore to a single site on the target
biomolecule. Indeed, there are a large number of fluorescent probes with
photochemical properties that are more attractive than tryptophan and
which are also sensitive to environmental changes. 5,11 By conjugating
these to proteins, nucleic acids, or lipids, the sensitivity and quality of
information provided by fluorescence spectrometry can be clearly
improved. Synthesized for the first time in 1871 by Adolf von Baeyer,