Study on binding area of benzodiazepine receptors by chemical modification

This paper first reports the effect of chemical modification on benzodiazepine receptor (BZ-R) reversible binding and photoaffinity labeling, and the hypothetical mechanism of BZ-R photoaffinity labeling. There was no effect on BZ-R reversible binding activity by modifying the amino group (-NH2) and the thiol group (-SH) of BZ-R, while the photoaffinity labeling between BZ-R and [methyl-3H]flunitrazepam ([3H]FNZP) was inactivated. The chemical modification of BZ-R by NBS inhibited both BZ-R reversible binding and photolabeling. The binding was inhibited 85 and 91%, respectively. FNZP added before NBS modification could prevent BZ-R from chemical modification. These results suggest that lysine (or arginine) and cysteine residues are the active groups in photoaffinity labeling, and tryptophan residue not only locates in BZ-R binding area but also is a necessary group of BZ-R binding. BZ-R reversible binding depends much more on the integration of receptor conformation than the photolabeling reaction.