Photodynamic Inactivation of the Na,K-ATPase Occurs via Different Pathways

Abstract

Abstract. The photodynamic, i.e., the light-induced, inactivation of the Na,K-ATPase in the presence of the sensitizer rose bengal was studied under different conditions. The shape of inactivation curves of the enzyme activity was analyzed as well as partial reactions of the pump cycle. Both experimental approaches showed the existence of two different time constants of inactivation of the ion pump, which reflect two pathways of a photodynamic modification. This is supported by the following observations: (1) The amplitude of the initial fast decay of enzyme activity was enhanced in the presence of D 2 O and reduced in the presence of the singlet oxygen scavenger imidazole. (Similar results were found for the SR Ca-ATPase.) (2) Contrary to the fast enzyme inactivation the slow process shows an inverse doserate behavior. (3) Inactivation of the partial reactions of Na + -binding and of K + -binding to the membrane domain of the Na,K-ATPase showed only a single time constant, which corresponded to the slower time constant of enzyme inactivation. In the presence of high concentrations of singlet oxygen the fast time constant dominated the inactivation of the ATP-induced partial reaction for which the cytoplasmic domains of the enzyme play an important role. The data support the conclusion that fast inactivation is due to modification of the cytoplasmic domains and slow inactivation due to modifications of the membrane domain of the ion pumps.

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

“…The influence by β -carotene of another quencher was not clear and may come from the insolubility of β -carotene. With D 2 O, inhibition by RB was promoted, suggesting, the 1 O 2 played a role in the inhibition function, because of the 16-time long reservation of 1 O 2 in 1 O 2 solution [25]; however, the quencher results were not complete but partial effects in our study. The reason is that UGT1A6 is not a soluble but a membrane-bound enzyme and is buried in lipid bilayers which protect UGT1A6 from 1 O 2 attack.…”

“…There are some papers on the inactivation of enzymes by xanthene dyes. 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].…”

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

“…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.…”

Photoactive antimicrobial agents/polyurethane finished leather

“…1(b)] is a xanthene photosensitizer with high‐absorption coefficient in the visible region of the spectrum and a tendency to transfer electrons from its excited triplet state, producing long‐lived radicals 6, 7. Therefore, RB has been exploited as a promising sensitizer in water treatment due to its water solubility, absorption in the visible region, good quantum yield of singlet oxygen, and inexpensiveness 8–10. The BP or RB containing PU leather finishing solutions were applied onto the surface of leather by a painting method.…”