Calcium complexes probes

Figure 2. Reporting of cytosolic free calcium levels by indo-1. Increases in cytosolic calcium, due either to entry of extracellular calcium via calcium channels or to release of intracellular calcium sequestered in organelles such as smooth endoplasmic reticulum, results in formation of the indo-l-calcium complex. Fluorescence intensity at 400 nm (excitation at 340 nm) is proportional to the concentration of this complex the dissociation constant for this complex is about 250 nff (24), making this probe useful for detecting calcium activities in the range of 25 to 2500 nJ. ...

Potentiometry (discussed in Chapter 5), which is of great practical importance, is a static (zero current) technique in which the information about the sample composition is obtained from measurement of the potential established across a membrane. Different types of membrane materials, possessing different ion-recognition processes, have been developed to impart high selectivity. The resulting potentiometric probes have thus been widely used for several decades for direct monitoring of ionic species such as protons or calcium, fluoride, and potassium ions in complex samples. 

Figure 3. Reporting of intracellular calcium sequestration by chlorotetracycline (CTC). CTC preferentially partitions into cell membranes and its fluorescence in this environment is sensitive to calcium bound to the membrane therefore its signal (excitation AOO nm, emission 530 nm) will come largely from organelles that bind or sequester calcium, such as smooth endoplasmic reticulum or mitochondria. Release of calcium from such organelles is accompanied by dissociation of the calcium-CTC complex, a decrease in CTC fluorescence and efflux of unbound probe from the organelle and from the cell.

A metal-nucleotide complex that exhibits low rates of ligand exchange as a result of substituting higher oxidation state metal ions with ionic radii nearly equal to the naturally bound metal ion. Such compounds can be prepared with chromium(III), cobalt(III), and rhodi-um(III) in place of magnesium or calcium ion. Because these exchange-inert complexes can be resolved into their various optically active isomers, they have proven to be powerful mechanistic probes, particularly for kinases, NTPases, and nucleotidyl transferases. In the case of Cr(III) coordination complexes with the two phosphates of ATP or ADP, the second phosphate becomes chiral, and the screw sense must be specified to describe the three-dimensional configuration of atoms. 

Figure 1. (Bottom) Diagram of the electrostatic potential adjacent to a membrane bearing a positive charge. The zeta potential is the potential at the hydrodynamic plane of shear, which should be about 2 A from the surface of the membrane. (Top) Schematic of the location of the probe molecules used to detect the potential produced by the adsorption of calcium and other alkaline earth cations to membranes formed from PC. The divalent cation cobalt and the amphipathic, anionic, fluorescent probe TNS will sense the potential at the interface. The non-actin-Rf complex will sense the potential in the center of the membrane.

Coordination chemistry of RE(III) with amino acids has been attracting much interest since the early 1970s after the discovery that certain RE(III) ions could be used as probes of calcium ion binding sites in proteins and enzymes [118, 119], Since then, a large amount of work on the solution and structural chemistry of rare earth-amino acid complexes has been published. The solution studies involve all of the rare earth elements and 13 (Gly, Ala, Val, Leu, Phe, Met, Pro, Ser, Tyr, His, Lys, Trp, and Arg) of the 20 standard amino acids, and more than 100 of the RE(III)-amino acid complexes have been structurally characterized. This section will cover the synthetic, structural, and solution chemistry of these complexes. 

There are many probes that report on cell activation via the concentration of other cellular molecules (e.g., calcium). We have simultaneously visualized fluo-antagonist binding and agonist-induced Ca2+ activation in single cells. Ideally, we would combine receptor density, location, and functional experiments to determine exactly which receptors, at what location, drive a particular form of activation. The individual components of this process can be digitally captured. However, visualization of such a complex multidimensional process has not yet been achieved. 

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