Heme proteins high spin forms

These workers have proposed that when heme proteins are crystallized, low-spin forms are favored in the equilibrium high-spin form low-spin form, and changes in conformation can also be involved. [A discussion of spin forms has been given by Kotani (1964).] The use of polarized spectra of single crystals permitted an assignment of all the absorption bands in the spectra. 

UV-Vis, ESR, and reflectance FT-IR spectroscopy were used to monitor protein conformation in the films. The Soret band for absorbance of visible light by the Fe(III)heme group of native Mb occurs at about 409 nm in solution, and at 410-414 nm for films of Mb alone. This band appears between 412 and 415 nm for films of the surfactants in Fig. 2 [19,24]. Completely denatured Mb gives a band at < 400 nm. Thus, results are consistent with native Mb in the surfactant films. ESR spectra are fully consistent with this view [24,49], and also indicate that the heme iron is in the high spin form with water as the sixth axial ligand. 

MCD spectroscopy in range 300 to 2000 nm at both ambient and liquid helium (4.2 K) temperatures can yield information about the spin, oxidation, and coordination states of each heme in a multiheme protein such as CCP (75). This technique, in combination with low-temperature X-band EPR spectroscopy, was used to great effect in characterizing the properties of the fully oxidized and MV forms of the P. aeruginosa CCP in solution. At 4.2 K, both hemes in the oxidized enzyme are low-spin ferric, with diagnostic features in the near infrared-MCD (NIR-MCD) spectrum consistent with one heme with His/Met axial coordination and the other with bis-histidine axial coordination this is entirely consistent with the crystal structure. In contrast, at room temperature only the low-potential (bis-histidine coordinated) heme in the C-terminal domain remains completely low-spin, whereas the high-potential (His/Met coordinated) heme exists as mixture of high- and low-spin forms 58). 

Electronic absorption maxima for LIP, MnP, horseradish peroxidase (HRP) and various llganded forms of these enzymes are shown in Table I. The spectra of native LIP and MnP are characteristic of high-spin ferric heme proteins, with Soret and visible maxima ( 407, 502 and... 

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