Search

Numerous phenolic compounds have been reported to have an inhibitory role on amyloid formation of proteins. The present study, utilizing lysozyme as a model system, examined the anti-amyloidogenic effects of phenol and three diphenol epimers. The results indicated that catechol and hydroquinone dose-dependently inhibited lysozyme fibrillation and covalently bound to the peptide chains to form quinoproteins, showing a similar effect to benzoquinone. In contrast, phenol and resorcinol did not modify the peptide with a quinone moiety, showing no effect on lysozyme fibrillation. We suggest that quinone intermediates are the active form for a phenolic compound to inhibit lysozyme fibrillation. The modification of lysozyme with quinone moieties alters the interacting forces between peptide chains and consequently interrupts the process of lysozyme fibrillation., (Copyright © 2012 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.)

Increasing evidence has demonstrated that EGCG possesses prooxidant potential in biological systems, including modifying proteins, breaking DNA strands and inducing the generation of reactive oxygen species. In the present study, the prooxidant effect of EGCG on erythrocyte membranes was investigated. SDS-PAGE and NBT-staining assay were utilized to detect the catechol-protein adducts that generated upon treating the membranes with EGCG. The results indicated that EGCG was able to bind covalently to sulfhydryl groups of membrane proteins, leading to the formation of protein aggregates with intermolecular cross-linking. We suggested that the catechol-quinone originated from the oxidation of EGCG acted as a cross-linker on which peptide chains were combined through thiol-S-alkylation at the C2- and C6-sites of the gallyl ring. EGC showed similar effects as EGCG on the ghost membranes, whereas ECG and EC did not, suggesting that a structure with a gallyl moiety is a prerequisite for a catechin to induce the aggregation of membrane proteins and to deplete membrane sulfhydryls. EDTA and ascorbic acid inhibited the EGCG-induced aggregation of membrane proteins by blocking the formation of catechol-quinone. The information of the present study may provide a fresh insight into the prooxidant effect and cytotoxicity of tea catechins., (Copyright © 2011 Elsevier Inc. All rights reserved.)