Photoinactivation of acetylcholinesterase by erythrosin B and related compounds

Abstract

Acetylcholinesterase was rapidly inactivated when exposed to light in the presence of xanthene dyes. Photosensitizing efficiency paralleled the dye triplet state quantum yields, increasing in the order fluorescein less than eosin B less than eosin Y less than erythrosin B less than rose bengal. The observed first-order rate constants of photoinactivation increased hyperbolically with dye concentration. Evidence for the formation of a dye-enzyme complex prior to inactivation was obtained from spectrophotometric and protein fluorescence quenching methods. The latter technique allowed estimates of the dye-enzyme dissociation constants for rose bengal (20 microM) and erythrosin B (30 microM). After photoinactivation, a portion of the dye became covalently bound to the enzyme. The photoinactivation reaction occurs in both aerobic (air saturated) and anaerobic (argon saturated) solution, with the rates of photoinactivation being about three to five times greater under the latter conditions. The aerobic reaction exhibits a large deuterium isotope enhancement effect and is largely (but not completely) quenched by 10(-2) M azide. The anaerobic reaction is unaffected by azide and exhibits only a small deuterium isotope effect. These results indicate that the photoinactivation reaction proceeds mainly by a type II (singlet oxygen mediated) pathway under aerobic conditions and by a type I (radical) pathway under anaerobic conditions. The enzyme was protected from inactivation by edrophonium, a competitive inhibitor, but not by d-tubocurarine, a peripheral-site ligand, indicating that destruction of a crucial residue at or near the catalytic site is an important component of the inactivation process. Extensive destruction of tryptophan undoubtedly occurs, at least under aerobic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition Mechanism of UDP-Glucuronosyltransferase 1A6 by Xanthene Food Dyes

“…[17][18][19][20][21][22] 8,14) Our previous results showed that the activity levels of CYP2A6 and UGT in bovine liver microsomes were similar to human liver microsomes 4,28,29) but differed from rat microsomes, as rat microsomes did not involve CYP2A6 activity. Thus, it was considered that bovine microsome data were very similar to human microsome data.…”

“…16) Meanwhile, phenyl-xanthene dyes, such as rose bengal (RB), ET, phloxine (PL), eosin (ES), uranine (UR), rhodamine (RM), and fluorescein are known as light-enhancing reagents (catalytic light reaction) by the generation of 1 O 2 on those dyes. [17][18][19][20][21][22][23] There are two types of reaction: the first is that drug energy enhanced by light is transferred to biomolecules and free radicals originate on the molecules. The second is that energy is transferred to oxygen, which changes to 1 O 2 .…”

“…Na,K-ATPase was inactivated by light in the presence of RB. 23,24) Acetylcholineesterase and some microorganims, such as Escherichia coli, Staphylococcus aureus, and influenza virus, are inactivated, 17,18,22,25) therefore, it is possible that xanthene dyes inactivate drug-metabolizing enzymes. 26) In the previous study, we clarified that RB inhibited the activity of UGT1A6 and CYP2A6 by mixed-type inhibitory mechanism.…”

Toxicity of Xanthene Food Dyes by Inhibition of Human Drug-Metabolizing Enzymes in a Noncompetitive Manner

“…Na,K-ATPase was inactivated by light in the presence of RB [24, 25]. Acetylcholineesterase and some microorganims, such as Escherichia coli , Staphylococcus aureus , and influenza virus, are inactivated [18, 19, 23, 26]. …”

Adsorption of xanthene food additive dyes to cellulose granules

“…There are some reports of inactivation of enzymes by xanthene dyes. Acetylcholine esterase (Tomlinson et al 1986) and some microorganisms such as Escherichia coli, Staphylococcus aureus (Wang et al 2006), and influenza virus (Lenard and Vandeloef 1993) are inactivated. So it is possible that xanthene dyes inactivate drug-metabolizing enzymes (Kuno and Mizutani 2005).…”