Photo-affinity label

Herbicidal Inhibition of Enzymes. The Hst of known en2yme inhibitors contains five principal categories group-specific reagents substrate or ground-state analogues, ie, rapidly reversible inhibitors affinity and photo-affinity labels suicide substrate, or inhibitors and transition-state, or reaction-intermediate, analogues, ie, slowly reversible inhibitors (106). 

Bergmann, K.E., Carlson, K.E., and Katzenellenbogen, J.A. (1994) Hexestrol diazirine photo-affinity labeling reagent for the estrogen receptor. Bioconjugate Chem. 5, 141-150. 

It has been demonstrated that cis- (76) and frarcs-flupentixol (75) (see Fig. 5) inhibited the photo affinity labeling of P-gp by substrate analogues [173] Binding of several MDR modulators, among them TFP (5), to P-gp was shown by means of fluorescence quenching of the MIANS probe [174] or P-gp tryptophan fluorescence [175]. CPZ (9) is likely a P-gp substrate, as was shown in studies of its transport in membrane vesicles obtained from multidrug-resistant CCRF-CEM cells [176], and therefore it was used as a competitive inhibitor of drug transport mediated by P-gp [177]. 

Routine syntheses of nucleotides have not been covered. Syntheses of more unusual derivatives have included adenosine and uridine 5 -(1-amino)ethylphos-phonate, which are unaffected by alkaline phosphatase, and 5-fluoro-2 -deoxy-uridine 5 V-azidophenylphosphate, used as a photo-affinity label for thymidylate synthetase. 

Phytohaemagglutinins.—pH-Acetyl]concanavalin A has been shown to bind to, and partially inhibit the enzymic activity of, proline 2-oxoglutaratedioxygenase. The products obtained when concanavalin A is labelled with 4-azidophenyl a-D-mannopyranoside under u.v.-irradiation have been separated by affinity chromatography on Sephadex G-lOO at pH 5. One of the products is a monovalent dimer at pH 5 and a divalent tetramer at pH 7, indicating that photo-affinity labelling did not alter the quaternary structure of concanavalin A, although the haemagglutinating activity of the derivatized lectin was reduced. 

Affinity Labeling by Other Mechanisms. Tw o types of controls are useful to establish that covalent linking takes place from the photo-affinity-labeled base of tRNA and not from another residue. First, there should be no linking in the absence of photolysis. While this may appear to be a trivial control, we have in fact observed such a light-independent covalent reaction with NAG-tRNA at the ribosomal A site, which otherwise had all the characteristics of a specific reaction in that labeling required EF-Tu and poly(U), and no labeling w as observed from the ribosomal P site. 

Maassen, J.A. and Moller, W., 1974, Identification by photo-affinity labelling of the proteins in Escherichia coli ribosomes involved in elongation factor G-dependent GDP binding, Proc. Nat. Acat. Sci. USA, 71 1277. 

Slipetz DM, Scoggan KA, Nicholson DW, Metters KM. Photo-affinity labelling and radiation inactivation of the leukotriene B4 receptor in human myeloid cells. Eur J Pharmacol 1993 244 161-173. 

Galardy, R. E., Craig, L. C., Jamieson, J. D., and Printz, M. P., 1974, Photo-affinity labeling of peptide hormone binding sites, /. Biol. Chem. 249 3510. 

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