The interaction of anions with native and phenylglyoxal-modified human serum transferrin.
The interaction of various anions with human serum transferrin was investigated due to the concomitant binding of iron and a synergistic anion to form the transferrin-anion-iron complex. Two tetrahedral oxyanion oxidizing agents, periodate and permanganate, were found to partially inactivate transferrin when used at equimolar ratios of oxidizing agent to protein active sites. Hypochlorite, a strong oxidizing agent with little structural similarity to periodate and permanganate, had little effect on iron-binding activity when used at similar low molar ratios of reagent to transferrin active sites. Transferrin treated with a 3:1 molar ratio of periodate or permanganate to active sites lost 74 or 67% of its iron-binding capacity, respectively. The composition of the buffer affected the extent of transferrin inactivation by periodate and permanganate; for example, the extent of inactivation by periodate was threefold greater in a borate buffer than in a phosphate buffer. Comparative oxidations in buffer systems suggest the following order of affinity of three buffer anions for the apotransferrin metal-binding center: phosphate greater than bicarbonate greater than borate. The interaction of phosphate ions with the iron-transferrin complex was also examined due to the increased susceptibility to periodate inactivation of iron-saturated transferrin in phosphate buffer (M. H. Penner, R. B. Yamasaki, D. T. Osuga, D. R. Babin, C. F. Meares, and R. E. Feeney (1983) Arch. Biochem. Biophys. 225, 740-747). The apparent destabilization of the iron-transferrin complex in phosphate buffer was found to be due to the competitive removal of iron by phosphate from the iron-protein complex. We found that phenylglyoxal-modified Fe-transferrin, with no loss of bound iron, was much more resistant to iron removal by phosphate and other competitive chelators.
D000447:Aldehydes; D000838:Anions; D001059:Apoproteins; D001639:Bicarbonates / Q000378:metabolism*; D001881:Borates / Q000378:metabolism*; D055598:Chemical Phenomena; D002621:Chemistry; D006801:Humans; D006997:Hypochlorous Acid / Q000494:pharmacology; D007501:Iron / Q000378:metabolism; D008345:Manganese / Q000494:pharmacology; D017895:Manganese Compounds; D010087:Oxides / Q000494:pharmacology; D010504:Periodic Acid / Q000494:pharmacology; D010658:Phenylglyoxal; D010710:Phosphates / Q000378:metabolism*; D013387:Succinic Anhydrides / Q000378:metabolism; D014168:Transferrin / Q000037:antagonists & inhibitors / Q000378:metabolism*
D000447:Aldehydes; D000838:Anions; D001059:Apoproteins; D001639:Bicarbonates; D001881:Borates; D017895:Manganese Compounds; D010087:Oxides; D010710:Phosphates; D013387:Succinic Anhydrides; D014168:Transferrin; C028284:apotransferrin; D010504:Periodic Acid; C048856:permanganic acid; D008345:Manganese; C031801:succinic anhydride; D006997:Hypochlorous Acid; C009288:metaperiodate; D007501:Iron; D010658:Phenylglyoxal