COMPLEXES OF IRON WITH PHENOLIC-COMPOUNDS FROM SOYBEAN NODULES AND OTHER LEGUME TISSUES - PROOXIDANT AND ANTIOXIDANT PROPERTIES

The low-molecular-mass fraction of the soybean nodule cytosol contains Fe capable of catalyzing free radical production through Fenton chemi stry. A large portion of the pool of catalytic Fe, measured as bleomyc in-detectable Fe, was characterized as complexes of Fe with phenolic c ompounds of three classes: phenolic acids, cinnamic acids, and flavono ids. Many of these compounds, along with other phenolics present in le gume tissues, were used for a systematic structure-activity relationsh ip study. All phenolics tested were able to chelate Fe, as judged from their inhibitory effect on site-specific deoxyribose degradation (min us EDTA assay). However, only those having catechol, pyrogallol, or 3- hydroxy-4-carbonyl groupings were potent chelators and reductants of F e3+ at pH 5.5. The same phenolics promoted oxidative damage to DNA (bl eomycin assay) and to deoxyribose (plus EDTA assay), but inhibited lin olenic acid peroxidation by chelating and reducing Fe3+ and by neutral izing lipid radicals. Also, phenolics having a pyrogallol nucleus atte nuated the free radical-mediated inactivation of glutamine synthetase, which was used as a model system, by chelating Fe2+. It is reasoned t hat under the microaerobic (10-20 nM O-2) and acidic (pH 5.5-6.4) cond itions prevailing in nodules, phenolics are likely to act primarily as antioxidants, decreasing oxidative damage to biomolecules. Copyright (C) 1997 Elsevier Science Inc.