Calcium fluorophores

Study of calcium ions in living cells has been immensely aided by calcium fluorophores (Box 6-D), which are often derivatives of EDTA (Table 6-9). One of these, calcein, is also very specific toward Fe. The natural calcium-dependent luminous protein, aequorin (Section J), is also widely used. 

Altinoglu El, Russin TJ, Kaiser JM, Barth BM, Eklund PC, Kester M, Adair JH (2008) Near-infrared emitting fluorophore-doped calcium phosphate nanoparticles for in vivo imaging of human breast cancer. ACS Nano 2 2075-2084... 

M-5 (Quin-2) was the first practical fluorescent indicator for cytosolic calcium with a simple 6-methoxyquinoline as its fluorophore. Ca2+-binding increases the fluorescence intensity about six-fold (without spectral displacement, in contrast to Fura 2 see Section 10.3.3). The fluorescence lifetime of Quin-2 is highly sensitive to calcium concentration Quin-2 can thus be used as a probe in the technique of fluorescence lifetime imaging. 

For practical applications it is better to use fluorescent probes excitable at high wavelengths, so that autofluorescence of the sample (especially biological samples) does not interfere. Calcium indicators based on fluorescein and rhodamine fluorophores(70) fulfill this requirement and are thus more convenient for fluorescence... 

Brown JQ, Srivastava R, McShane MJ. Encapsulation of glucose oxidase and an oxygen-quenched fluorophore in polyelectrolyte-coated calcium alginate microspheres as optical glucose sensor systems. Biosensors Bioelectronics 2005, 21, 212-216. 

Fig. 8.2. Examples of ion exchange, monitored by FCS. (a) FITC measured at different pH. Decays of the correlation curves in the 1ms, 2-80 xs, and l xs time range are attributed to translational diffusion, proton exchange and single-triplet state transitions of the fluorophores, respectively, (b) FITC at pH6, with different concentrations of phosphate buffer. Inset Measured fcprot vs. concentration of buffer/salt at pH6. (c) FCS curves of GFP (S65T) at different pH. (d) The calcium sensitive dye Rh-II, measured at different concentrations of free calcium...

Fig. 4. A molecular OR gate in the shape of compound 3. With both proton and calcium ion sensitivity, the tertiary amine atom will quench fluorescence of the fluorophore a in the absence of both stimuli. The presence of one b or c the other stimulus reduces the ability of the nitrogen lone pair to participate in PET. The same is true when d both stimuli are added to the solution...

Marriott and Heidecker reported a Cys-caged heavy meromyosin (HMM) using DMNB-Br and evaluated the capacity of photoactivated HMM to couple the energy of calcium/actin-activated ATP hydrolysis to the movement of F-actin filaments in an in vitro motility assay [29, 86], It was known from labeling studies with the thiol-reactive fluorophore tetramethylrhodamine... 

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