Biology Reference
In-Depth Information
III. DM-Nitrophen
A. Chemical Properties
Graham Ellis-Davies followed a di
erent strategy for releasing Ca 2 þ —by
attaching a 2-nitrobenzyl group to one of the chelating amines of ethylenediami-
netetraacetic acid (EDTA) to form the photosensitive chelator dimethoxynitro-
phenyl-EDTA or DM-nitrophen ( Ellis-Davies and Kaplan, 1988; Kaplan and
Ellis-Davies, 1988 ). Photolysis by UV light in the wavelength range 330-380 nm
cleaves the DM-nitrophen with a quantum e
V
ciency of 0.18 through multiple
intermediate pathways ( McCray et al., 1992 ) to form iminodiacetic acid and a
H þ -absorbing 2-nitrosoacetophenone derivative, with 65% of the photoproducts
formed with a time constant of 15 m s and the rest with
Y
1.9 ms ( Faas et al., 2005,
2007 ). A simplified reaction is shown in Fig. 3 . Although DM-nitrophen binds
Ca 2 þ with an a
t ¼
nity of 7 nM at pH 7.2, Ca 2 þ -bound chelator forms a photoprod-
uct-binding Ca 2 þ with a 4-mM a
Y
nity, while the free form (and Mg 2 þ -bound
forms, see below) photolyze to a 90 m M-K D photoproduct at an ionic strength of
150 mM. These values are from the most recent of the continually evolving models
of DM-nitropen photolysis ( Ayer and Zucker, 1999; Bollmann and Sakmann,
2005; Faas et al., 2005, 2007; Kaplan and Ellis-Davies, 1988; Neher and Zucker,
1993 ). Thus, complete photolysis of Ca 2 þ -DM-nitrophen can elevate Ca 2 þ over
50,000-fold, much more than photolysis of the nitr compounds or azid-1. This
significant advantage is counterbalanced to some extent by the facts that the
photoproducts bu
Y
er Ca 2 þ so weakly that the final [Ca 2 þ ] i will be determined
largely by native cytoplasmic bu
V
ers, and that the Ca 2 þ liberated by photolysis of
DM-nitrophen will be removed more readily by extrusion and uptake pumps.
V
CO
Ca 2+
CO
O 2 C
CO
CO
O 2 C
N
N
Ca 2+
N
O
NO 2
NO
CO
CO
h n
+
N
H
OCH 3
OCH 3
OCH 3
OCH 3
DM-nitrophen
(high Ca 2+ affinity)
DM-nitrophen photolysis products
(low Ca 2+ affinity)
Fig. 3
Structure of and reaction scheme for DM-nitrophen, which releases calcium on exposure to
light.
 
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