Photochemical labeling

Gorman, J.J., and Folk, J.E. (1980) Transglutaminase amine substrates for photochemical labeling and cleavable cross-linking of proteins./. Biol. Chem. 255, 1175. 

In general, it is advisable to perform photochemical labeling in the absence of oxygen (Chapter 4). Occasionally, with the less common reagents, a requirement for the presence of oxygen has been noted, e.g. for the reaction of 4-thio-UMP with ribonuclease (Sawada and Kanbayashi, 1973), and when covalent attachment of dyes occurs during photo-oxidation experiments (Brandt et al., 1974). 

The thermal reaction between trans-[Co(CN)4(S03)2]5- and 13CN- in aqueous solution results in stereospecific incorporation of label to form tranj-[Co(13CN)(CN)4(S03)]4, whereas when the reaction is carried out photochemically, labelled cyanide is randomly incorporated.71 Photodisso-ciative loss of SO2- appears to lead to an electronically or vibrationally excited intermediate which has a chemistry quite distinct from the intermediate produced in the thermal reaction. Whatever its exact nature, the photoexcited intermediate has a short configurational lifetime and this causes random introduction of l3CN-. 

Light-induced charge separation was treated in the porphyrin section 4.4, activities of entrapped dyes in section 4.5. In the following, we discuss the effect of vesicle viscosity on photoreactions and photochemical labelling. 

The location of binding of EF-Tu on ribosomes has been established directly by cryo-EM. It binds both to the L7/L12 stalk and to the body of the 505 ribosomal subunit. The other end of the P site is at the pepti-dyltransferase locus and has been photochemically labeled by azide derivatives of aminoacyl groups bound to a tRNA. The labeling is primarily in the 505 subunit of E. coli ribosomes and involves the central loop of domain V (residues 2043 - 2625) of the 235 RNA. Residues U2584 and U2585 are major sites of crosslinking (see Fig. 29-14). The presence of nearby sites of mutation leading to resistance to chloramphenicol or erythromycin (Box 29-B) served to confirm the central loop as part of the peptidyltrans-ferase. Domain II of 235 RNA is also involved, and there is evidence that the unique sequence UGG at positions 807-809 may also interact with the CCA end of tRNA in the P site. ... 

Biomembranes are not static structures, but are rather built on a fluid lipid matrix (Chapman, 1975). Mass spectrometry offers interesting possibilities in the area of affinity labelling, particularly photochemical labelling aimed at the formation of crosslinks between nearest neighbours in membranes. We shall focus our attention on the problem of lipid-lipid interactions, as studied by MS. 

The labeling site should be both saturable and show saturation kinetics for photochemical labeling. The half-maximally effective ligand concentration should be close to the binding or inhibition constant of the ligand in a biological assay (see, e.g., references cited in footnotes 24, 52, 60, 95, 96). 

Low extents of labeling, and nonspecific labeling, have been the two major difficulties encountered in photochemical labeling studies. Low... 

Trifluoromethyl derivatives of diazirines have been largely used as precursors of carbenes, as an example for indole derivatives, 8 for the functionalization of C60 fullerene and for photochemical labeling of biological molecules. 

Photochemical labeling via azides has been largely applied. The introduction of a photoreactive azide groups is often used for following a biochemical path, as in the case of a dopamine transporter. ... 

Attempts to detect initial structures either using isotope exchange followed by a chemical or NMR analysis in order to identify the formation of local structures, or methods such as differential labeling or photochemical labeling are accessible approaches. The existence of intermediates in the folding pathway is rather well established however, the nature of these intermediates is generally not yet identified. 

Recall that the symmetry labels e and o refer to the symmetries of the orbitals under reflection through the one Cy plane that is preserved throughout the proposed disrotatory closing. Low-energy configurations (assuming one is interested in the thermal or low-lying photochemically excited-state reactivity of this system) for the reactant molecule and their overall space and spin symmetry are as follows ... 

Chlonne-36-labeled 1,1-dichlorotetrafluoroethane is produced photochemically from chlonne-36 and l-chloro-l,2,2,2-tetrafluoroethane in better than 90% yield [22]... 

Shimomura, O., and Johnson, F. H. (1979c). Elimination of the effect of contaminating CO2 in the lsO-labeling of the CO2 produced in biolu-minescent reactions. Photochem. Photobiol. 30 89-91. 

Complexed arenediazonium salts are stabilized against photochemical degradation (Bartsch et al., 1977). This effect was studied in the former German Democratic Republic in the context of research and development work on diazo copying processes (Israel, 1982 Becker et al., 1984) as well as in China (Liu et al., 1989). The comparison of diazonium ion complexation by 18-crown-6 and dibenzo-18-crown-6 is most interesting. Becker at al. (1984) found mainly the products of heterolytic dediazoniation when 18-crown-6 was present in photolyses with a medium pressure mercury lamp, but products of homolysis appeared in the presence of dibenzo-18-crown-6. The dibenzo host complex exhibited a charge-transfer absorption on the bathochromic slope of the diazonio band. Results on the photo-CIDNP effect in the 15N NMR spectra of isotopically labeled diazonium salts complexed by dibenzo-18-crown-6 indicate that the primary step is a single electron transfer. 

Oswald B, Gruber M, Bohmer M, Lehmann F, Probst M, Wolfbeis OS (2001) Novel diode laser-compatible fluorophores and their application to single molecule detection, protein labeling and fluorescence resonance energy transfer immunoassay. Photochem Photobiol 74 237-245... 

Campbell, R, and Gioannini, T.L. (1979) The use of benzophenone as a photoaffinity label. Labeling in p-benzoylphenylacetyl chymotrypsin at unit efficiency. Photochem. Photobiol. 29, 883. 

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