Variational theory for g tensor in electron paramagnetic resonance experiments: application to ferricytochrome c and azidomyoglobin

1989 ◽  
Vol 93 (1) ◽  
pp. 194-200 ◽  
Author(s):  
J. N. Roy ◽  
K. C. Mishra ◽  
Santosh K. Mishra ◽  
T. P. Das
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Variational Theory ◽  
Paramagnetic Resonance ◽  
Ferricytochrome C ◽  
Electron Paramagnetic

Electron Paramagnetic Resonance Study of Single Crystals of Horse Heart Ferricytochrome c at 4.2 °K

1972 ◽  
Vol 50 (10) ◽  
pp. 1048-1055 ◽  
Author(s):  
Colin Mailer ◽  
C. P. S. Taylor
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Single Crystals ◽  
Electron Paramagnetic Resonance Study ◽  
Field Potential ◽  
Personal Communication ◽  
Chem Phys ◽  
Paramagnetic Resonance ◽  
Ferricytochrome C ◽  
G Value ◽  
Electron Paramagnetic

Electron paramagnetic resonance (E.P.R.) spectra from single crystals of horse heart ferricytochrome c at 4.2 °K were analyzed to obtain the orientation of the principal g values relative to the crystallographic axes. The axis of the largest principal g value (g3 = 3.06) was within 5° of the heme normal direction reported in the X-ray structure of the same crystals (Dickerson et al.: J. Biol. Chem. 246, 1511 (1971)). The other two g axes (g1 = 1.25, g2 = 2.25) lie within 5° of the N–Fe–N directions in the heme ring, in contrast to met-myoglobin azide (Helcké et al.: Proc. R. Soc. B169, 275 (1968)) and cyanide (Blumberg, W. E.: personal communication) where they lie ~ 45° from the N–Fe–N directions. A version of Eisenberger and Pershan's theory (J. Chem. Phys. 47, 327 (1967)) was used to explain the 400–2000 G variation in linewidth on crystal rotation. The results were explained by combining the broadening produced by a distribution of rhombic crystal field potential (r.m.s. deviation 11%) over the molecular population, with that from a variation in the directions of the principal g values caused by misorientation (r.m.s. deviation 1.5°) of the molecules in the crystal.

The pH-Induced Transition of Iodinated Ferricytochrome c: Electron Paramagnetic Resonance and Absorption Spectra

1973 ◽  
Vol 51 (4) ◽  
pp. 472-475 ◽  
Author(s):  
R. A. Morton
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Liquid Nitrogen Temperature ◽  
Heme Iron ◽  
Paramagnetic Resonance ◽  
Frozen Solution ◽  
Type Iii ◽  
Type Iv ◽  
Ferricytochrome C ◽  
Iron Coordination ◽  
Electron Paramagnetic

The heme-associated, pH-induced transition in iodinated ferricytochrome c has been studied by electron paramagnetic resonance (E.P.R.) and absorption spectroscopy. The conversion from type III to type IV (as defined by Theorell, H., and Åkesson, Å.: J. Am. Chem. Soc. 63, 1812 (1941)) ferricytochrome c forms was dramatically altered by iodination of tyrosyl residues. Both absorption and E.P.R. spectra suggested that a transition between similar heme-iron coordination structures occurred with a pK of about 6 as compared with about 9 for native ferricytochrome c. At pH 4.4 the E.P.R. spectrum (liquid nitrogen temperature) of a frozen solution of iodinated ferricytochrome c was similar to the native type III at pH 7, except for an increased g = 6.0 signal from high-spin heme iron. At neutral pH the E.P.R. spectrum of the iodinated derivative was similar to type IV ferricytochrome c. The results give further support to the hypothesis that the pK of tyrosine 67 plays an important role in determining the pK of the III to IV transition.

The Electron Paramagnetic Resonance Spectrum of Ferricytochrome c and Lysine-Modified Derivatives at Alkaline pH

1973 ◽  
Vol 51 (4) ◽  
pp. 465-471 ◽  
Author(s):  
R. A. Morton
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Liquid Nitrogen ◽  
Liquid Nitrogen Temperature ◽  
Alkaline Ph ◽  
Coordination Structure ◽  
Paramagnetic Resonance ◽  
Type Iii ◽  
Type Iv ◽  
Ferricytochrome C ◽  
Electron Paramagnetic

The heme-associated, pH-induced transition of ferricytochrome c and two lysine-modified derivatives was investigated by absorption and electron paramagnetic resonance (E.P.R.) spectroscopy. The transition from type III to type IV ferricytochrome c (as defined by Theorell, H., and Åkesson, Å.: J. Am. Chem. Soc. 63, 1812 (1941)) produced a new E.P.R. spectrum in frozen solution measured at liquid nitrogen temperature. The measured g values were 3.2 and 2.1 (9.16 GHz). The third component of the expected set of three principal g values for low-spin type IV ferricytochrome c was not observed in this study. In two derivatives with modified lysyl residues, trifluoroacetylated and guanidinated ferricytochrome c, the type III to type IV transition was absent, and instead, at alkaline pH, a brown–red form was produced which had a strong absorption band at about 605 nm. The apparent pK's were 10.3 (trifluoroacetylated) and 9.4 (guanidinated). When an alkaline solution of the guanidinated ferricytochrome was frozen, the E.P.R. spectrum had a set of sharp lines (g values 2.79, 2.21, and 1.76) similar to those observed from low-spin type V ferricytochrome c (pH 14). The alkaline trifluoroacetylated protein gave a similar set of signals but in addition contained the signals observed at neutral pH. These results were interpreted by assuming that, at alkaline pH, a hydroxide ion displaced one of the normally coordinated iron ligands with a temperature-dependent equilibrium between high-spin and low-spin states. Freezing the solution to liquid nitrogen temperature shifted the equilibrium to the low-spin form, and, for the trifluoroacetylated derivative, led to partial recovery of the coordination structure present at about pH 7. The E.P.R. spectrum of the guanidinated cytochrome at neutral pH indicated that the iron electronic structure was essentially identical to type III ferricytochrome c. In contrast, the E.P.R. spectrum of the trifluoroacetylated protein was significantly different, but whether the coordination structure has been geometrically distorted or chemically changed remains to be determined.

The Electron Paramagnetic Resonance Spectrum at 77 °K of Lyophilized and Frozen Solutions of Horse Heart Ferricytochrome c

1971 ◽  
Vol 49 (3) ◽  
pp. 328-331 ◽  
Author(s):  
R. A. Morton ◽  
T. L. Bohan
Keyword(s):  
Molecular Structure ◽  
Electron Paramagnetic Resonance ◽  
Electron Paramagnetic Resonance Spectrum ◽  
Resonance Spectrum ◽  
Paramagnetic Resonance ◽  
Commercial Preparation ◽  
Frozen Solution ◽  
Ferricytochrome C ◽  
Frozen Solutions ◽  
Electron Paramagnetic

The electron paramagnetic resonance spectrum of a repurified, commercial preparation of horse heart ferricytochrome c was measured both in frozen solution, and as a lyophilized powder at 77 °K. The solution spectrum agreed with previous measurements reported at 20 °K. The lyophilized powder had both high-spin (g ~ 6), and low-spin components. The latter were significantly different from that of the solution spectrum. Thus, the molecular structure of the protein near the iron atom must be considerably, but reversibly, distorted by drying. In addition, it was suggested that a g = 4.29 line was due to acid-denatured forms of cytochrome c present as an impurity.

The Temperature Dependence of the Electron Paramagnetic Resonance Spectrum of Ferricytochrome c Solutions Between 4.2 °K and 77 °K

1971 ◽  
Vol 49 (6) ◽  
pp. 695-699 ◽  
Author(s):  
C. Mailer ◽  
C. P. S. Taylor
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Temperature Dependence ◽  
Electron Spin ◽  
Heme Iron ◽  
Spin Lattice Relaxation ◽  
Paramagnetic Resonance ◽  
Gaussian Shape ◽  
Electron Spin Relaxation ◽  
Ferricytochrome C ◽  
Electron Paramagnetic

Electron paramagnetic resonance (E.P.R.) signals from tuna ferricytochrome c solutions were obtained in the temperature range 4.2–77 °K. The microwave power and temperature dependence of the spectra obtained fit the theory for a Kramer's doublet split by a magnetic field. The g-values obtained are 1.25, 2.24, and 3.05 in agreement with other workers (Salmeen, I., and Palmer, G.: J. Chem. Phys. 48, 2049 (1968)). The g = 3.05 line changes from 380 G wide at 20–40 °K with Gaussian shape to 700 G wide at 77 °K with Lorentzian shape. Analysis shows that the Gaussian shape can be explained by variation in the rhombic symmetry of the heme iron environment, a ± 6% spread in rhombic potential being required to give a 380 G line width. At higher temperatures the line appears to be determined by the electron spin-lattice relaxation time. Below 20 °K the E.P.R. absorption signal is saturated, and a large E.P.R. dispersion signal appears, due to fast passage effects, which can be used to give further information on electron spin relaxation times.

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