Free-Radicals: Chemistry and Biology...Spin Trapping Transition metal 16. Nitric Oxide/NOS 17....
Transcript of Free-Radicals: Chemistry and Biology...Spin Trapping Transition metal 16. Nitric Oxide/NOS 17....
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Free-Radicals:
Chemistry and BiologyProf. Attilio Citterio
Dipartimento CMIC “Giulio Natta”
http://iscamap.chem.polimi.it/citterio/education/free-radical-chemistry/
Department CMIC
Lecture 16 – FR16
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Attilio Citterio
Content
1. Introduction Current Status of Radicals Chemistry
What is a Radical
Free Radicals and Life
2. Historical Aspects
3. Electronic Structure and Bonding
4. Active Oxygen Specie, O2, O2
•-·, HO2•, 1O2, H2O2, HO•
Chemistry
H2O2 and peroxides
5. Radical Reactions• Atom transfer
• Addition to multiple bonds
• Homolytic Aromatic Substitution
• Electron Transfer (oxidation-reduction)
6. Thermodynamics
7. Free Radical Kinetics First-order Reaction
Second-order Reaction
Steady-State
Chain-reactions
Redox chain reactions
Inhibition
8. Radiation Chemistry Tools
Specie: e‾(aq), H•, HO•, H2O2, H2, O2•‾
Pulse Radiolysis/Flash Photolysis
9. Lipid Peroxidation Chemistry
Measurement
Effects
10. Antioxidants Preventive
Chain-breaking
Small molecule (Vit. C/E, CoQ, Urate).
Enzymes
Chelates
11. Iron and Free Radical Chemistry Reactions
Complexes and redox chemistry
12. DNA and Protein (As radical targets)
13. Photo reactions Photochemistry Photosensitization
14. Detection of Radicals TBARS
Fluorescence
Cyt. C /NBT
Chemiluminescence
15. EPR Detection of Radicals Direct Detection
Spin Trapping
Transition metal
16. Nitric Oxide/NOS
17. Oxygen radicals/ROS
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Reactive Nitrogen Species (RNS)
Nitric Oxide / NOSProf. Attilio Citterio
Dipartimento CMIC “Giulio Natta”
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Attilio Citterio
Reactive Nitrogen Species (RNS)
Radicals:
NO• Nitric Oxide
NO2• Nitrogen dioxide
Non-Radicals:
ONOO‾ Peroxynitrite
ROONO Alkyl peroxynitrites
N2O3 Dinitrogen trioxide
N2O4 Dinitrogen tetroxide
HNO2 Nitrous acid
NO2+ Nitronium cation
NO‾ Nitroxyl anion
NO+ Nitrosyl cation
NO2Cl Nitryl chloride
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Attilio Citterio
Nitric Oxide
Persistent radical, until 1989 considered only a pollutant. Then, identified
as a fundamental signaling agent in cells biochemistry with relevant
physiological roles.
Bond Order
= (1/2) [8– 3]
= 2.5
O N
1 s bond
1 p bond
1 “3 electrons” bond
s2p*
p2p*
s2p
p2p
s2s*
s2s
E
Nitric oxide: a molecule of millennium! Circ Res 2000, 87, 85-7.
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Attilio Citterio
Synthesis and Fate of Nitric Oxide in Living
Systems
NOproduction
Chloroplast
Cytoplasm
Chloroplast
PeroxisomesMitochondria
AtNOS1(AtNOA1)?
NO2‾
NO2‾
L-Arginine
Mitochondria
Cytoplasm NO2‾
Nitratereductase
(NR)
Nitrite: NO reductase (Ni-NOR)
Plasma membrane
(root)
NO2‾
(a)
NO
Removal by GSH
and hemoglobin's
Activation of
MAP kinases
Stimuli
e.g. ABA
Thiol group competitionfrom other ROS
Enz-SHS-nitrosylation
Activation of GTP cyclase
Altered gene expression
Altered
enzyme
activity
Increased synthesis
Enz-Tyr nitration
tcGMP
tcADPR t Ca2+
RYP
(b)
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Attilio Citterio
Brief Summary of Nitric Oxide Chemistry
.NO
NO2. ONOO‾
RNO
NO‾
Me-NO
NO+
anti-oxidant
pro-oxidant
one-electron
redox
one-electron
redox
O2 O2.–
R.Me
+ e–
– e–
H. Rubo & R. Radi In Handbook of Antioxidants Cadenas & Packer, Eds., pp. 689-707 (2001)
(E = +0.79 V)(E = +1.0 V)
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Attilio Citterio
NO in Plant
Journal of Experimental Botany 66(10):2827-2837 · April 2015
PLANT CELL
Non-enzymatic
NADPHNADH
NO2‾
L-Arginine
NOS
NR
O2‾GSH
NO
ONOO●
NO2●
Tyrosinenitration NO2-FA
Cell signaling
GSNO
Cys-SNO
ProteinS-nitrosylation
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Attilio Citterio
Reactions of •NO with Other
Free Radicals
Oxidation of NO to NO2 and nitrite:
2 NO + O--O 2 NO2
4 NO + O--O + 2H2O 4HNO2
Nitric oxide reaction with organic alkyl and peroxy radicals:
NO + R RNO R2N-O
NO + ROO ROONO ??
Reaction with superoxide ion and NO2:
O2•‾ + •NO ‾OON=O
ONOONO 2NO2•
NO2• + •NO N2O3
R
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Attilio Citterio
Nitric Oxide Biological Functions
• Cell signaling/effector agent
• increases intracellular levels of cGMP in smooth muscle tissue
• vase-relaxant
• inhibits cell (platelet) adhesion and aggregation
• also made in brain and mitochondria
• Drugs sources of NO: nitro-vasodilator (amyl-nitrite, nitroglycerine)
• Modification of biological molecules by NO via reaction with R-SH
regulator of metal metabolism
RS + NO RS-NO
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Attilio Citterio
Main Biological Chemistry of •NO
• Binding of NO to ferrous heme iron of guanylate cyclase
The first major reaction is binding of NO to ferrous heme iron of guanylate
cyclase or other proteins. This is important for the activation of signal
transduction pathways
Heme—Fe2+ + .NO → Heme—Fe2+—NO
• Reaction with oxyhemoglobin
The second reaction and certainly the major route for the destruction of NO
in vivo is the fast and irreversible reaction with oxyhemoglobin to nitrate:
Hb—Fe2+ —O2 + .NO → Hb—Fe3+ + NO3
-
• Reaction with superoxide anion
The third reaction is the fast (diffusion-controlled) and irreversible reaction
of nitric oxide with superoxide anion to yield peroxynitrite (ONOOˉ):
• Reaction with oxygen
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Attilio Citterio
Reaction with Superoxide Anion
O2 •ˉ +
.NO → ONOOˉ
k = 1.9×1010 M–1·s–1
Peroxynitrite: E°’ = +1.4 V
• Peroxynitrite is in rapid protonation equilibrium with peroxynitrous acid
ONOO– a ONOOH pKa = 6.8
• Peroxynitrous acid may decompose to HO• and NO2•
ONOOH a [HO.
…. NO2.]
• Chemical reactivity includes oxidations and nitrations
[HO.
…. NO2.] + RH → R
.+ H2O + NO2
•
R• + NO2• → RNO2
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Attilio Citterio
Pro-oxidant Properties of Nitric Oxide
• 3-Nitrotyrosine, a fingerprint of peroxynitrite reactivity
Tyr Tyr.
Tyr–NO2
[HO.
…. NO2.] H2O NO2
.
O2.–
.NO
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Attilio Citterio
Nitric Oxide Synthases (NOS-family)
NOS
eNOS, nNOS
Constitutively expressed, regulated by
Ca2+/calmodulin
iNOS
Highly induced after immune stimulation
(LPS, cytokines)
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Attilio Citterio
Nitric Oxide Synthase
Nature Structural Biology 1999, 6, 233 – 242.Biochemistry, 2002, 41, 11073
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Attilio Citterio
Redox Cascade to Fe2+/Fe3+
FADH•NADPH
NADP+ FADH2 FMNH•
FMNH2 Fe3+
Fe2+
-320 mV -280 mV -274 mV -248 mV
FAD
FMNFAD
FMN
Fe
NADPH
Arginine + O2
Citrulline + NO
Arginine + O2
Citrulline + NO
NADPH
Fe
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Attilio Citterio
In vivo Generation of •NO:
Nitric Oxide Synthase (NOS)
L-Arg
BH4
Oxygenase
domain
Reductase
domain
Calmoduline
module
FMN FADNADP+
Chem. Rev. 2002, 102, 1191-1199.
Two
cycles
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Attilio Citterio
Reduction of Oxygen by Oxygenases
H2O
Fe3+
S
RH
e‾
O2
e‾
I
II
III
IV
P•+VII
2 H2O
peroxide shunt
H+
H+
H2O
RHR(O)H
V
VI
H+
Fe3+
S
Fe2+
S
OOH
Fe3+
S
O22‾
Fe3+
S
O2
Fe2+
S
O2‾
Fe3+
S
O2‾
Fe4+
S
Chem. Rev. 2002, 102, 1191-1199;
Curr. Op. in Chem. Bio. 1999, 3:131-
137
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Attilio Citterio
Oxygenation of Arginine by Iron Enzymes
Fe3+
S
Fe3+
S
Arginine
O2
BH4
I
II
III
IV
VI
VII
H+
H2O
Arginine
O2•ˉ
Uncoupledturnover
ArgOH
BH3•
FMNH•
FMNH•ˉ
FMN
FMNH•
Fe2+
S
Fe2+
S
O
2Fe3+
S
O2•‾
Fe3+
S
OOH
P•+
O2 ‾
Fe4+
S
OHˉ
Fe4+
S
P
O2ˉ
Fe4+
S
P•+
Fe3+
S
P
H abstraction
oxygen
rebound
NH
NH2HN
R
OH
+ NH
NH2H2N
R
+
NH
NH2HN
R
+
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Attilio Citterio
In the Absence of Donor Protein
Fe3+
S
Fe2+
S
Fe3+
S
ArgOH
O2O2•ˉ
Fe3+
S
I
II
III
IV
VI
OOH
Fe3+
S
FMNH
2FMNH•
ArgOHArgO•
H+
H2O
ArgO•
NO + Cit.
O2
Fe2+
S
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Attilio Citterio
•NO Generation Detail of Mechanism
O
Fe3+
S
O- H
NH
NH2HN
+
R
O•
S
NH
NH2N
R
H
H
O
O
Fe3+
O
S
Fe3+
NH
R
NH2O
H2O
O=N•
O
Fe3+
S
O•-
I(ferric)IV(oxy) VI(hydroperoxy)TETRAHEDRAL
INTERMEDIATE
NH
R
O
NH2HN
H
+
hydroxyarginine citrulline
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Attilio Citterio
Peroxynitrite
nitrate tyrosine
oxidise lipids, DNA
NO + O2•- → ONOO
-
Nitric oxide + superoxide → peroxynitrite
Protein kinases ion channels
+ +
GMP
phosphodi
esterase
NO
GTP
cGMP
guanylate
cyclase
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Attilio Citterio
Peroxynitrite (PON) as a Free Radical Producer
Beckman and co-workers were the first to propose that when overproduced, •NO
was likely to react with O2•- to form peroxynitrite (PON) (Beckman et al., Proc Natl
Acad Sci. USA 87:1620, 1990). This seminal paper attracted much attention
because based on scanty chemical literature and on the oxidation of DMSO and
deoxyribose, it proposed that (PON) could be a transition metal ion-independent
route for hydroxyl radical production in vivo.
pKa= 6.6ONOOHONOO‾ + H+ [•NO2
•OH]
(DMSO/ deoxyribose)
•NO + O2•‾k ~1010 M-1·s-1
This led to many papers and to a huge controversy about the possibility of free
radical production from (PON) in vitro. The controversy was resolved and the
oxidant is likely to act as free radical producer in vivo. Relevant is the rapid
reaction of (PON) with the biologically ubiquitous CO2 that increases (PON)‾
mediated one-electron oxidation and nitration of biomolecules. In some
environments, reaction of (PON) with hemeproteins may also become
important for biomolecule--derived radical production.
(Augusto et al., Free Rad Biol Med. 32:849, 2002).
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Attilio Citterio
Proton-catalyzed Decomposition of
Peroxinitrite
Peroxynitrite is stable at alkaline pH but upon protonation (pKa = 6.6) it
decomposes to yield 70% NO3‾ and 30% •OH and •NO2 that can oxidize
biomolecules (BM) to the corresponding radicals. In vivo, however,
these one-electron oxidations are likely to become relevant only at acid
pH because at neutral pH the proton-catalyzed decay is too slow to
compete with bio targets such as CO2, bio thiols (RSH) and
hemoproteins P-Fe(III) that react directly with peroxynitrite
ONOO‾
k ~ 102 - 106 M-1·s-1
CO2
BM
(RSH, P-Fe(III)) BMox
(RSOH, P•+-Fe=O)
k = 3 × 104 M-1·s-1
ONOOHH+
[ONO• •OH]cagepKa = 6.6
0.7 NO3‾ + 0.7 H+
0.3 •NO2 + 0.3 •OH
slow
k = 0.17 s-1
(PTyr, RSH)
BM•
BM
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Attilio Citterio
Peroxynitrite Reactions in vitro:
Two- versus One-Electron Oxidations
RSH, P-Fe(III) and CO2 are anticipated to be the most important peroxynitrite bio
targets because of their high biological concentrations and rapid reaction rate
with the oxidant (k ~ 102-106 M-1·s-1). These reactions greatly reduce the half-life
of peroxynitrite (from s to ms) and the targets are usually oxidized by two-
electron mechanisms. An important exception is the reaction with the biologically
ubiquitous CO2 that produces 65% NO3‾ and 35% CO3•‾ and •NO2 (Bonini et al.,
J Biol Chem. 274:10802, 1999).
k ~ 102-106 M-1·s-1
CO2
BM(RSH, P-Fe(III)) BM ox
(RSOH, P•+-Fe=O)
k = 3×104 M-1·s-10.35 CO3
•‾ + 0.35 •NO2
0.65 NO3‾ + 0.65 CO2
ONO • • O─C
O
O‾ cage
ONOO‾H+
ONOOHEPR detection of CO3
•‾ during
fast-flow mixing of ONOO‾ and HCO3‾
g = 2.0113
20 G12CO3•‾
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Attilio Citterio
Peroxynitrite as a biomolecule-derived
radical producer
(i) Peroxynitrite is likely to act through its derived radicals (CO3•‾ and
•NO2) in vivo due to the high concentration of CO2 in equilibrium with HCO3‾ in most biological fluids. In low pH environments, the peroxynitrite-derived •OH radical can also become relevant.
(ii) Both, CO3•‾ (E°’ = 1.8 V; pH 7.0) and •NO2 (E°’ = 0.9 V, pH = 7.0) are
oxidizing radicals that can oxidize several bio targets to their corresponding radicals. A flux of both radicals (as produced from peroxynitrite) is very efficient in nitrating tyrosine and guanine residues by combining the oxidizing power of CO3
•‾ with the radical recombination reactions of •NO2
(iii) The main biomolecules that are likely to be oxidized to their corresponding radicals by peroxynitrite-derived radicals in vivo are GSH, P-SH, P-Tyr, P-Trp, RNA-Gua and DNA-Gua.
(iv) Oxidation of GSH to GS•, occurs even in environments where peroxynitrite reacts preferentially with hemoproteins rather than with CO2. Then, oxidation of GSH to GS• is likely to be a consequence of peroxynitrite production in vivo.
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Attilio Citterio
Cis-trans Isomerization
• •NO2 can induce cis-trans isomerization of cis double bonds in
unsaturated fatty acids
LNO2: Lipid derived
signaling mediators?
Cis-trans isomerization
and vinyl-nitro products
Vinyl-nitro Product
Alkyl-nitro Product
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Attilio Citterio
Nitric Oxide as Cellular Response Signal
Cell line
Bioactivity
Stimulation GlutamateAcetylcholine
BradykininLipopolysaccharide
Cytokline
Macrophage
NO NO NO
Endothelium-derived
relaxing factor NeurotransmitterAntibacterial activity
tumor cell killing
NeuronEndothelial cell
Palmer et al. Nature 1988 Brenman et al. Cell 1996 Xie et al. Science 1992
Blood pressure control
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Attilio Citterio
NO• Signaling in Physiology
Nitric Oxide Synthase
NO•
Binds to heme moiety of guanylate cyclase
Conformational change of the enzyme
Increased activity (production of cGMP)
Modulation of activity of other proteins (protein
kinases, phospho-diesterases, ion channels)
Physiological response (relaxation of smooth muscles, inhibition of
platelet aggregation, etc.)
O2•‾ ONOO‾
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Attilio Citterio
Electrochemical Nitric Oxide Sensor
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Attilio Citterio
Advantages and Disadvantages of Chemiluminescence
Compared to Other Methods of NO Detection
• Advantages
High Sensitivity and Linearity over a Broad Concentration Range
Good Reproducibility and High Specificity for NO (few other
gaseous substances (DMSO, ethylene) react with ozone)
Measurements Possible in Turbid or Colored Samples, Even at
Extreme pH (in solution, in the headspace, in expired air)
Besides Mass Spectrometry the Only Other Method that Allows
Quantification of Absolute Amounts of Nitroso Species
Moderate Running Costs
• Disadvantages
With Some Biological Samples Difficult to Extract NO into Gas
Phase
Provides Limited Structural Information
Limited Sample Throughput, High Purchase Price for Detector
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Attilio Citterio
Photolysis/Chemiluminescence Approach for
Detection of Nitroso Species
Reaction principle: RSNO RS• + NO.
R2NNO R2N• + NO.
Discrimination of RSNOs from other nitroso species and nitrite by measurement
before and after HgCl2 treatment, and with lamp ON and OFF
Stamler et al., 1992, Alpert et al., 1997
light
light
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Attilio Citterio
Sample Processing Using Redox-Active
Reaction Mixtures - Many Choices, Many Pitfalls
Most techniques use Chemical Reactions to convert nitroso and nitrosyl species into NO,
which is then detected by chemiluminescence
• Reducing mixtures differ largely in reducing strengths and reduction capacity
Iodine/iodide (I3-) 60 mM I-/6-20 mM I2/ 1M HCl, RT Samouilov & Zweier, 1998
56 mM I-/ 2 mM I2, 4mM CuCl, CH3COOH, 68°C Marley et al., 2000
60 mM I-/10 mM I2, CH3COOH, 60°C Feelisch et al., 2002
Cysteine/CuCl 1 mM L-cysteine, 0.1 mM CuCl Fang et al., 1998
Hydroquinone/Quinone 0.1/0.01 mM Samouilov & Zweier, 1998
VCl3/H+ 0.1 M in 2M HCl Ewing et al., 1998
• Oxidizing mixture for determination of NO-hemes
Ferricyanide 0.2 M in PBS pH 7.5 Gladwin et al., 2002
Bryan et al, 2004
General Problem:
Neither method is absolutely specific and bears the potential to produce false positive
(nitrate, L-NitroArg, ...) or negative signals
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Attilio Citterio
Reaction Chambers Come in Many Different
Designs
Menon et al., 1991
Cox & Frank, 1982
Dunham et al., 1995
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Attilio Citterio
The Most Frequently Used Type of
Chemiluminescence Set-up
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Attilio Citterio
Which NO-Related Species are Detected and
How can they be Discriminated from One Another?
• Without Reduction Step:
NO (direct injection into buffer or water)
• Upon Acidification:
NO2- (disproportionation of HNO2)
RONO (acid-catalyzed decomposition)
• With Sample Reduction:
NO2-/NO3
- (KI/CH3COOH, RT for nitrite,
VCl3/H+, 90°C for nitrate)
RSNO
RNNO (I3-/CH3COOH, 60°C)
NO-Heme
detection limit: 1-50 nM, depending on flow and inj. volume
250 fmoles NO (at 50 µL injection vol.)
• Discrimination between different species:
Selective NO2- removal Sulfanilamide/H+
RSNOs from other Nitroso-Species HgCl2/sulfanilamide
Nitroso from Nitrosyl Species Reducing vs. Oxidizing Reaction Mix
0 5 10 15 60 65
0
10
20
30
NitriteGSNO
SNOAlb
NOW NOHb
Nitrite
NO
[pbb]
Time [min]
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Attilio Citterio
Bio-imaging of Nitric Oxide Using DAF-2
Detection principle:
Reaction of aromatic vicinal diamines with NO in the presence of oxygen to
produce the corresponding triazenes
Advantages: Sensitivity for NO (5 nM in vitro) with high temporal and spatial resolution
No cross-reactivity to NO2-/NO3
- and ONOO-
Assay limitations: Possible interference by reducing agents and divalent cations, pH sensitive,
subject to photo bleaching, requiring standardized illumination conditions
DAF-2 DA DAF-2 DAF-2 T
non-fluorescent,
cell-permeable
non-fluorescent fluorescent,
Ex 495 nm, Em 515 nm
esterases NOx
cell membrane
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Attilio Citterio
Recent Developments
• Development and commercial availability of red fluorescent chromophores (diamino-rhodamine-based; DAR-4M) increases flexibility for combinations with other green-fluorescent probes and shows reduced interference with tissue auto fluorescence, but is otherwise very similar to DAF-2
• Difluoroboradiaza-s-indacene based fluorophore (similar chemistry)
• Detection of nitroso peptides and proteins on diaminofluoresceine gels(standard SDS-PAGE followed by UV photolysis in the presence of DAF-2 or DAF-FM for detection of C-, O-, N- and S-nitrosated compounds) (Mannick et al, 2005)
• Near-Infrared fluorescent probes for „NO“ detection in isolated organs(tricarbocyanine as NIR fluorochrome coupled to o-phenylenediamine as NO sensor; NIR is potentially very interesting for in vivo imaging approaches as it allows deeper penetration of light into tissues and shows no interference with tissue autofluorescence; promising novel approach
(Nagano et al, 2005)
• Amplifier-coupled fluorescent NO indicator with nanomolar sensitivity in living cells(genetically encoded fluorescent indicator based on the binding of NO to soluble guanyl cyclase and detection of formed cGMP by FRET; interesting, but potentially problematic cross-talk with cGMP generated by particulate GC and modulation of sensitivity by PDE activity)
(Sato et al, 2005)