Tyrosine sensor

Suzuki H., Tamiya E. and Karube I. (1989) A hybrid L-tyrosine sensor using an enzyme and bacterial CO2 sensor. Anal. Letters, 22, 15-24. 

Tissue also contains some endogenous species that exhibit fluorescence, such as aromatic amino acids present in proteins (phenylalanine, tyrosine, and tryptophan), pyridine nucleotide enzyme cofactors (e.g., oxidized nicotinamide adenine dinucleotide, NADH pyridoxal phosphate flavin adenine dinucleotide, FAD), and cross-links between the collagen and the elastin in extracellular matrix.100 These typically possess excitation maxima in the ultraviolet, short natural lifetimes, and low quantum yields (see Table 10.1 for examples), but their characteristics strongly depend on whether they are bound to proteins. Excitation of these molecules would elicit background emission that would contaminate the emission due to implanted sensors, resulting in baseline offsets or even major spectral shifts in extreme cases therefore, it is necessary to carefully select fluorophores for implants. It is also noteworthy that the lifetimes are fairly short, such that use of longer lifetime emitters in sensors would allow lifetime-resolved measurements to extract sensor emission from overriding tissue fluorescence. 

Figure 16.7 Schematic representation illustrating the selective diffusion of dopamine over glutamic acid and tyrosine into the mesopores of PLA-coated MSN-based fluorescence sensor system.

Lawrence, D.S. and Q. Wang. 2007. Seeing is beheving peptide-based fluorescent sensors of protein tyrosine kinase activity. Chem. BioChem. 8, 373-378. 

An early attempt to make a real electrochemical sensor based on a molecularly imprinted methacrylate polymer utilised conductometric measurements on a field-effect capacitor [76]. A thin film of phenylalanine anilide-imprinted MAA-EDMA copolymer was deposited on the surface of semiconducting p-type silicon and covered with a perforated platinum electrode. An AC potential was applied between this electrode and an aluminium electrode on the back side of the semiconductor and the capacitance measured as a function of the potential when the device was exposed to the analyte in ethanol. The print molecule could be distinguished from phenylalanine but not from tyrosine anilide and the results were very variable between devices, which was attributed to difficulties in the film production. The mechanism by which analyte bound to the polymer might influence the capacitance is again rather unclear. 

D. Chin and A.R. Means. 2000. Calmodulin a prototypical calcium sensor Trends Cell Biol. 10 322-328. (PubMedl A.P. Dawson. 1997. Calcium signalling How do IP3 receptors work Curr. Biol. 7 R544-R547. (PubMedl Protein kinases, including receptor tyrosine kinases... 

This system is employed by prokaryotic organisms, and homologous pathways have recently been identified in eukaryotes. The prototypical two-component pathway consists of two proteins A protein histidine kinase (sensor kinase) and a response regulator. Histidine kinases are very distinct from the superfamily of conventional protein serine/threonine and tyrosine kinases. The histidine kinases auto-phosphorylate on histidine residues and are involved in the phosphorylation of aspartate amino acids and their targets. 

RNP-based fluorescent probes would be ideal to detect protein tyrosine phosphorylation directly in the solution. To develop a fluorescent RNP sensor for the pTyr residue, RNP receptors has been developed for the pTyr residue.57 RNP receptors for pTyr were isolated from a pool of RNA sequences (430) as described... 

The following substrates can be determined with almost identical sensitivity by using D-amino acid oxidase in combination with an ammonium ion sensitive electrode D-alanine, D-leucine, D-norleucine, D-methionine, and D-phenylalanine. L-amino acid oxidase sensors have been described for L-leucine, L-cysteine, L-methionine, L-tryptophan, and L-tyrosine (Guilbault and Hrabankova, 1971), and L-histidine and L-arginine (Tran-Minh and Broun, 1975). 

Yao and Wasa (1988a) assembled modified electrodes for amino acids by crosslinking L- or D-amino acid oxidase with glutaraldehyde on silanized platinum probes. The sensors were employed as detectors in high pressure liquid chromatography. Whereas the L-amino acid oxidase electrode responded to L-tyrosine, L-leucine, L-methionine, and L-phenylalanine in amounts as low as 2 pmoles, the D-amino acid electrode measured only D-methionine and D-tyrosine. The response time in steady state measurements was only 5-10 s. 

Decarboxylases of phenylalanine, tyrosine, and lysine and ammonia lyases of histidine, glutamine, and asparagine are also highly selective. Guilbault et al. (1988) described a potentiometric enzyme sensor for the determination of the artificial sweetener aspartame (L-aspartyl-L-phen-ylalanine methylester) based on L-aspartase (EC 4.3.1.1). The ammonia liberated in the enzyme reaction created a slope of 30 mV/decade for the enzyme-covered ammonia sensitive electrode. The specificity of the sensor was excellent however, the measuring time of 40 min per sample appears not to be acceptable. The measuring time has been decreased to about 20 min by coimmobilizing carboxypeptidase A with L-aspartase (Fatibello-Filho et al., 1988). 

Toyota et al. (1985) developed a protein assay with use of a tyrosinase sensor. Tyrosine was measured after complete proteolysis of the sample by pepsin. The results agreed well with those obtained by the method of Lowry. 

Figure 1 Potential supramoleciiLar sensors for potassium (top) and tyrosine (bottom)...

An enzyme sensor based on tyrosine can be used for assay of phenolic compounds at the millimole-per-liter level.103 The method is based on the following reactions ... 

---