Analysis of low-spin ESR spectra of ferric heme proteins: A reexamination

Bohan, Thomas L.

doi:10.1016/0022-2364(77)90240-2

Cited by 48 publications

(42 citation statements)

References 12 publications

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“…Highly anisotropic low-spin (HALS) hemes have been known since the early work of Griffith ( 27, 28 ), Blumberg and Peisach ( 29, 30 ), Taylor ( 31 ), Bohan ( 32 ), Loew ( 33 ), Walker ( 26, 34-36 ) and many others (for reviews see ref. ( 35, 37, 38 )).…”

Section: Discussionmentioning

confidence: 99%

Role of Calcium in Metalloenzymes: Effects of Calcium Removal on the Axial Ligation Geometry and Magnetic Properties of the Catalytic Diheme Center in MauG

Chen¹,

Naik²,

Krzystek

et al. 2012

Biochemistry

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MauG is a diheme enzyme possessing a five-coordinate high-spin heme with an axial His ligand and a six-coordinate low-spin heme with His-Tyr axial ligation. A Ca2+ ion is linked to the two hemes via hydrogen-bond networks, and the enzyme activity depends on its presence. Removal of Ca2+ alters the EPR signals of each ferric heme such that the intensity of the high-spin heme was decreased and the low-spin heme was significantly broadened. Addition of Ca2+ back to the sample restored the original EPR signals and enzyme activity. The molecular basis for this Ca2+-dependent behavior was studied by magnetic spectroscopy. The results show that in the Ca2+-depleted MauG the high-spin heme was converted to low-spin and the original low-spin heme exhibited a change in relative orientations of its two axial ligands. The properties of these two hemes are each different than in native MauG and are now similar to each other. The EPR spectrum of Ca2+-free MauG appears to describe one set of low-spin ferric heme signals with a large gmax and g-anisotropy and a greatly altered electromagnetic relaxation property. Both EPR and Mössbauer spectroscopic results show that the two hemes are present as unusual highly axial low-spin (HALS)-like hemes in Ca2+-depleted MauG, with a smaller orientation angle between the two axial ligand planes. These findings provide insight into the correlation of the enzyme activity with the orientation of axial heme ligands, and describe a role for the calcium ion in maintaining this structural orientation that is required for activity.

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Section: Discussionmentioning

confidence: 99%

Role of Calcium in Metalloenzymes: Effects of Calcium Removal on the Axial Ligation Geometry and Magnetic Properties of the Catalytic Diheme Center in MauG

Chen¹,

Naik²,

Krzystek

et al. 2012

Biochemistry

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“…The apparent g factors were determined using the WINEPR or XeprView programs (Bruker). The ligand field parameters were calculated from the experimental g values using a method previously described (41)(42)(43). The obtained values are summarized in Table S1 together with representative values of relevant cysteine thiolate ligation of heme from the literature.…”

Section: Methodsmentioning

confidence: 99%

Heme impairs the ball-and-chain inactivation of potassium channels

Sahoo

Goradia

Ohlenschläger

et al. 2013

Proc. Natl. Acad. Sci. U.S.A.

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Significance Heme, traditionally viewed as a stable protein cofactor such as in hemoglobin, also serves as an acute signaling molecule and is cytotoxic at high concentrations. Here, we show that free intracellular heme potently enhances A-type potassium channel function. Such channels determine action potential frequency in excitable cells, and their dysfunction often contributes to pathological hyperexcitability, such as in pain and epilepsy. Binding of free heme at nanomolar concentrations to the “ball-and-chain” N terminus of A-type potassium channels, which typically closes the channels, introduces a stable structure in the otherwise disordered region and allows for a greater efflux of potassium ions, thus reducing cellular excitability. Heme therefore could be a powerful negative-feedback regulator in brain and muscle function.

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“…11,25,28,29) Blumberg 28) and Peisach et al 29) proposed two crystal field parameters: rhombicity (jR= j) and tetragonality (j = j), both calculated from three g values in various types of low-spin ferric heme complexes. Table 1 shows, for the present samples, the crystal field parameters, calculated by employing a method developed by Bohan,30) together with those for P450-ligand systems for comparison. A crystal field diagram constructed from the data in Table 1 is shown in Fig.…”

Section: Chemical Treatment and Crystal Field Analysismentioning

confidence: 99%