Study Of The Metalloporphyrins Catalyzed Protein Tyrosine Nitration

Protein tyrosine nitration is an oxidative post-translational modification that affects protein structure and function and attributes to the pathogenesis of many inflammatory diseases.Metal porphyrins,iron porphyrins and manganese porphyrins,function as highly active peroxynitrite decomposition catalysts at physiological pH and temperature and protect cells from either exogenously introduced or endogenously induced peroxynitrite damage.However,under inflammatory conditions,it is most likely that several nitrating pathways operate simultaneously.For example,hemin or heme peroxidase/H₂O₂/NO₂^-system cause protein tyrosine nitration in hemolytic diseases and atherosclerotic plaque.Hence,it becomes interesting to know whether other hemin water-soluble derivatives,such as iron porphyrins and manganese porphyrins,effectively catalyze protein tyrosine nitration in vitro in the presence of H₂O₂ and NO₂^-.And the finding will surely provide a great contribution in the designing of balanced therapies for pharmacological intervention in peroxynitrite related diseases.We systemically investigated catalytic properties of FeTPPS,FeTMPyP and FeTBAP on protein nitration.The study showed that FeTPPS,FeTBAP and FeTMPyP all exhibited higher peroxidase activity in compared with hemin.FeTPPS and FeTBAP could effectively catalyze BSA nitration in the presence of H₂O₂ and NO₂^-,but FeTMPyP failed to do so.By comparing with FeTPPS and FeTBAP,FeTMPyP can more rapidly scavenge oxo-Fe（IV）intermediates of FeTMPyP by significant self-degradation,resulting in the shortest lifetimes of O=Fe^IV–TMPyP,O=Fe^IV-TMPyP^+·and the lowest catalytic activity on oxidation tyrosine and nitrite,which might be the principle factor on FeTMPyP inactivation in protein nitration.The failed binding may keep away of target residue of BSA from the center of FeTMPyP center where the RNS is generated,which might be another minor factor on FeTMPyP inactivation in protein nitration.Water-soluble manganese porphyrin,such as MnTPPS,MnTMPyP and MnTBAP,are efficient peroxynitrite reductase when coupled with biological antioxidants.Hence,we investigated the effect of manganese porphyrins catalysed protein tyrosine nitration to find the properties of central metal of porphyrins on protein nitration.By the dot blotting,we found that the quantity of protein tyrosine nitration calatyzed by MnTPPS and MnTBAP reached the maximum at pH=8,which were involved in the different principle in contrast to that of FeTPPS and FeTBAP.But MnTMPyP failed to do so,which was similar to FeTMPyP.In the further study,we raised the hypothesis that the oxidation of tyrosine to tyrosine radical was promoted as pH increased,but the high potential of oxidation nitrite was as barriers at high pH that inhibited the formation of nitrogen dioxide radical.