Redox Reactions of Metalloporphyrins in Biological Systems

The concept of the photosynthetic and respiratory systems is that they are based on the rapid flow of electrons through a graded sequence of redox steps mediated by a continuous sequence of carriers [Change (27)]. Hemoproteins play an important role here, as do other organic carriers like quinones, flavins, and copper and iron proteins. 

Heme Proteins which Bind and/or Activate Molecular Oxygen Hemoglobin 

The structural changes in the hemoglobin subunits, accompanying the oxygenation of hemoglobin have been attributed to a 0.8-A shift of the iron atoms out of the porphyrin planes [Perutz (145)]. If this 

The heme enzyme, tryptophan dioxygenase, activates molecular oxygen to undergo the following reaction [Cragh (125), Yamamoto (215), Marks (128)  

In this case the formation of the superoxide anion from molecular oxygen has been substantiated by quenching experiments with superoxide dismutase [Brady (14), Strobel (169), Hirata (93)), although these cannot be accepted as definite proof because the specifity of the enzyme for superoxide anions has not been conclusively demonstrated. 

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