RESUMO
BACKGROUND: Many changes can occur in proteins, including amino acid modification, fragmentation, changes in absorption and fluorescence spectra and others. All these modifications can be used as markers of protein damage by free radicals. AIM OF THE WORK: The aim of the present study was to investigate the antioxidant activities of the aqueous extracts of dry green of pods Phaseolus vulgaris, leaves of Olea europaea, unripe fruits of Bitter melon and leaves of Morus nigra. The pro-oxidant activities of the aqueous extracts of the above plants towards protein and estimation of some markers of the protein oxidation were also investigated. METHODS: The antioxidant activities of the above plants extracts, such as superoxide dismutase (SOD)- like and scavenging of diphenyl picrylhydrazyl (DPPH) radicals were observed. A soluble protein (bovine serum albumin: BSA) was incubated with different concentrations of the aqueous extracts of the plants of the present study. An aliquot from this mixture was used for sodium dodecyl sulphate/polyacrylamide gel electrophoresis (SDS-PAGE). Oxidative protein damage was assessed as tryptophan oxidation, carbonyl, quenone and advanced oxidation protein products (AOPP) generation in BSA in separate aliquots of the mixture. RESULTS: All the plant extracts of this study had an antioxidant activity, but the aqueous extracts of both Olea europaea and Morus nigra leaves showed the highest antioxidant activities. In addition only the extracts of the Olea europaea and Morus nigra leaves showed highly oxidative fragmentation on BSA, but not the other plant extracts, which was evaluated by sodium dodecyl sulphate/polyacrylamide gel electrophoresis (SDS-PAGE) technique. The increase in protein oxidation products was in concentration dependent manner. The carbonyl, quenone and AOPP contents were highly significantly elevated in Olea europaea and Morus nigra leaves-treated protein when compared to the control protein. The tryptophan fluorescence was also significantly decreased in Olea europaea and Morus nigra leaves-treated protein when compared to the control sample. CONCLUSION: [corrected] These data demonstrate the antioxidant and pro-oxidant activities of the aqueous extracts of the plants examined, while the highly effective are Olea europaea and Morus nigra leaves. The pro-oxidant activity of these plant extracts may be attributed to the unstable state of their phenoxyl radicals.
