The electrocatalytic reactions of cysteine and cystine by water-soluble iron porphyrin, manganese porphyrin and iron(II) phenanthrolines

The electrocatalytic reduction of L-cystine to L-cysteine and the reduction of the oxidized form of glutathione to the reduced form of glutathione by the (FeTSPP)-T-I species was investigated in aqueous solution. The electrocatalytic oxidations of L-cysteine to L-cystine by FeTSPP, Mn(4-TMPyP), iron(II) tris(3,4,7,8-tetramethyl-1,10-phenanthroline) and iron(II) tris(1,10-phenanthroline) were investigated in aqueous buffer solutions at room temperature. The water-soluble iron tetrakis(4-sulfonatophenyl)porphine (FeTSPP) catalyzed the rapid reduction of L-cystine to L-cysteine after using an electrochemical method to reduce (FeTSPP)-T-III and the iron (III) mu-oxo dimer (TSPP)Fe-III-O-Fe-III(TSPP) to the (FeTSPP)-T-I species. Iron(II) tris(1,10-phenanthroline) and iron(II) tris(3,4,7,8-tetramethyl-1,10-phenanthroline) may perform the electrocatalytic oxidation of L-cysteine to L-cystine. (FeTSPP)-T-III was reduced to (FeTSPP)-T-II by L-cysteine or the reduced form of glutathione. L-cysteine or the reduced form of glutathione were oxidized in a basic solution. If [Fe-III(TSPP)](3-) is oxidized to [Fe-III(TSPP.+)](2-) by electrochemical method, it can oxidize L-cysteine to L-cystine electrocatalytically or oxidize the reduced form of glutathione in strong acidic solutions. If Mn-III(4-TMPyP) is also reduced by L-cysteine to Mn-II(4-TMPyP), L-cysteine oxidizes to L-cystine. The electrocatalytic oxidation of L-cysteine to L-cystine by Mn(4-TMPyP) is performed by two different pathways. Mn-III(4-TMPyP) is oxidized to either Mn-III(4-TMPyP) or Mn-IV(4-TMPyP) by the electrochemical method, then Mn-IV(4-TMPyP) or Mn-III(4-TMPyP) oxidizes L-cysteine to L-cystine. An electrocatalytic oxidation of L-cysteine similar to the oxidation by Mn-IV(4-TMPyP) or Mn-III(4-TMPyP) can also be performed by the reduced form of glutathione. (C) 1997 Elsevier Science Ltd.