Tyrosine isothiocyanates

XU K and thornalley p j (2001) Signal transduction activated by the cancer chemopreventive isothiocyanates cleavage of BID protein, tyrosine phosphorylation and activation of INK , Br J Cancer, 84 670-73. 

Isothiocyanates react with nucleophiles such as amines, sulfhydryls, and the phenolate ion of tyrosine side chains (Podhradsky et al., 1979). The only stable product, however, is with primary amine groups, and so TRITC is almost entirely selective for modifying s- and N-terminal amines in proteins. The reaction involves attack of the nucleophile on the central, electrophilic... 

Lysine may also present problems because its e-amine couples with phenyl-isothiocyanate to form the e-phenylthiocarbamyl derivative, which is sensitive to any trace of peroxides in the sequencer solvents that may decrease its yield. Its chromatographic elution close to leucine frequently requires special attention to gradient conditions as well. Tryptophan, tyrosine, and methionine are sensitive to severe oxidation, although this is usually an infrequent problem, especially with the latter two. Those residues with sidechains containing only carbon and hydrogen (e.g., Ala, Val, lie. Leu, and Phe) are the most stable and are not known to present any complications from the Edman degradation procedure. 

Capillary zone electrophoresis with microchip-based SCCE has been used to separate fluorescent dye from degradation products and to separate fluorescein isothiocyanate (FITC) labeled amino acids. Capillary zone electrophoresis (CZE) in fused-silica capillaries has been used to separate the racemic mixtures of (a-hydroxybenzyl)methyltrimethylammonium and (2-hydroxy-l-phenyl)ethyltrimethylammonium with f)-cyclodextrin as the chiral pseudo-stationary phase. L-Phenylalanine and L-phenylalanine-ring-D5 (the hydrogens in the aromatic ring were substituted with deuterium) and another separation of the closely related amino acids phenylalanine and tyrosine have been resolved using CZE with capillary-based SCCE. ... 

Sulphhydryl groups react with fluorescein isothiocyanate, and phenolic groups (of tyrosine) react to a small extent under the above reaction conditions. Fluorescein thiohydantions in amounts exceeding 1 nmol are visible as yellow spots on TLC plates and show up as intense greenish-yellow fluorescent spots under UV light. 

Sinalbin p-hydroxybenzyl isothiocyanate Tyrosine Brassica alba... 

Progoitrin 2-hydroxy-3-butenyl isothiocyanate Tyrosine Brassica oleracea... 

Figure 3 shows data obtained in another device, Jet-1, with the layout indicated in the figure. The resistances of each of the channels of this device were determined as described above. The separation of fluorescein isothiocyanate (FITC) labelled arginine (arg) and tyrosine (tyr) is shown. For these experiments sample solution was present in reservoir 2, which was held at ground. As shown in the diagram at the top, samples were injected across a "double T" injector towards reservoir 1, which was at -3 kV. This injector creates a sample plug in the separation channel about 150 pm in length. 

Isothiocyanates also react with the hydroxyl group of tyrosine and other hydroxyamino acids. The addition of a hydroxy compound usually yields N-substituted thiocarbamates, which are esters of AT-substituted thiocarbamoic acids (Figure 2.67). 

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