Hemeproteins ferric

Although, relevant information about ferrous hemeproteins kinetics, dynamics and ligand photodissociation pathways has been obtain, less is known about ferric hemeproteins photophysic processes. Recent studies performed with Hbl-CN and Mb-CN at ultrafast time scale, have suggested that some of the transients intermediaries observed after ferrous complexes ligand photodissociation are observed in ferric Mb and Hbl [7], However, time-resolved infrared data shows that the complex remained six coordinated after photoexcitation. In this work we present ultrafast data on ferric Hbl-NO, HM-N3, HM-H2S and metHbl complexes that suggest a mechanism for the photoinduced reduction of Hbl species. 

The intermediate-spin state has been suggested both for ferrous (21) and ferric hemeproteins (22, 23). Direct participation of the intermediate-spin iron porphyrins in biological processes might be less probable however, any reasonable theoretical account of the varied electronic structure of iron in hemeproteins should explain the fact that the so-called intermediate-spin iron porphyrin can exist only when the axial ligand field is extremely weak. 

Figure 1 shows that after photoexcitation the ferric complexes HM-H2S, Hbl-N3, Hbl-NO and metHbl exhibit an absorption transient formation near -435 nm, which were formed in -300 fs. Time decays varies from 4.5 ps to 6 ps. More than 95 % of signal recovery was observed within 20 ps after photoexcitation. These transients appear to be similar to those observed and assigned to a reduced species of ferrous hemeprotein complexes [6]. An absorption transient formation at 455 nm was also observed and corresponds to formation of the excited states Hbn [3]. As with the ferrous Hbl complexes, the species formed was observed immediately... 

Pin S, Hickel B, Alpert B, Ferradini C. (1989) Parameters controlling the kinetics of ferric and ferrous hemeproteins reduction by hydrated electrons. Biochim Biophys Acta 994 47-51. 

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