Luminescence studies on physostigmine, rubreserine and adrenochrome

Physostigmine and Galanthamine Bind in the Presence of Agonist at the Canonical and Noncanonical Subunit Interfaces of a Nicotinic Acetylcholine Receptor

“…This was determined by sequence analysis of α subunit fragments beginning at αTrp-118/αThr-119, which were produced by cyanogen bromide cleavage of rpHPLC-purified αV8-18. While we detected photolabeling only of tyrosines and cysteines, it is likely that different photolysis conditions will favor the formation of rubreserine, a chemically reactive o -quinone decomposition product of physostigmine (Savory and Turnbull, 1985) that reacts efficiently with the primary amine of lysine. However, since o -quinones do not react with tyrosines (Pierpont, 1969), the photolabeled nAChR tyrosines that we have identified reflect photolabeling by [ 3 H]physostigmine and not by an o -quinone decomposition product.…”

“…Photolysis at 312 nm for 5 min resulted in maximal [ 3 H]physostigmine incorporation with minimum protein damage (as judged by aggregation); for [ 3 H]galanthamine, photolysis at 312 for 10 min was optimal. Photodecomposition of physostigmine at 312 nm produces rubreserine, a chemically reactive o-quinone that can cross-link proteins (Savory and Turnbull, 1985), while phototolysis of galanthamine does not produce similar reactive intermediates (Marques et al, 2011). Consistent with the formation of rubreserine, we found in control experiments with non-radioactive physostigmine in TPS that irradiation at 312 nm resulted in the formation of a red reaction product with an absorption peak at 500 nm (t 1/2 ~5 min).…”