CHAPTER 19 MOLECULAR IMAGING 409
A
B
0.2
0.4
0.6
0.8
1.0
(a)
0.0
300 350 400 450 500 550
Absorbance
Wavelength (nm)
0.2
0.4
0.6
0.8
1.0
(b)
0.0
56789
Normalized fluorescence
pH
Figure 19.5The pH dependence of the optical spectrum of YFP. (a) The amplitudes of the
two absorption bands have a distinct pH dependence with an isosbestic point. (b) The relative
amplitude can be fit to a pH dependence with a pKAof 7. Modified from Elsliger et al. (1999).
O
O
cyclization
H 2 O
H 2 O
dehydrogenation
second
dehydrogenation
DsRed
chromophore
GFP
chromophore
HO
R
O
NH
O (^2) O
O
HO
N
N
R
O
NH
O
O
HO
N
N
R
O
N
O
O
HO
N
N
R
O 2
O
NH
N
NH
H
O
Figure 19.6A general scheme for chromophore formation in GFPs consisting of a cyclization step
followed by dehydration. In DsRed, the chromophore undergoes an additional step that results in a
longer conjugated system. Modified from Matz et al. (2003).