Reactions of triethylphosphine gold(I) complexes with heme proteins: novel spin-state changes in cytochrome b562, myoglobin, and hemoglobin.

Reactions of bacterial Fe(III) cyt b562, HbO2, met Hb and met Mb with Et3PAuCl and Et3PAuNO3 (and some related complexes) have been investigated by electronic absorption and EPR and NMR spectroscopy. Except for met Hb, which denatured, the products were novel high-spin Fe(III) heme proteins. The reactions of cyt b562 and Mb were reversible. Two distinct kinetic steps were observed in the autoxidation of HbO2 and MbO2. These may involve the liberation of superoxide. Autoxidation of HbO2 occurred more rapidly than that of MbO2. The kinetics of the spin-state change of cyt b562 were too fast to measure by conventional (spectrophotometric) methods. The reaction of Et3PAuCl with HbO2 was not blocked by N-ethylmaleimide. The reactions are discussed in terms of attack by Et3PAu+ on histidine residues in the hydrophobic haem pockets of the proteins.