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T Yonetani

Publications and source records attributed to T Yonetani.

At least 37 records · Page 2Linked to original sources
PubMed1993

Oxygen equilibrium studies of cross-linked iron-cobalt hybrid hemoglobins. Models for partially ligated intermediates of cobalt hemoglobin.

To probe the molecular mechanism of allosteric function of cobaltous protoporphyrin-substituted hemoglobin (CoHb), a series of alpha, alpha-cross-linked symmetric and asymmetric Fe-Co hybrid hemoglobins, which contain (1Co porphyrin/3Fe porphyrins), (2Co porphyrins/2Fe porphyrins), and (3Co porphyrins/1Fe porphyrin) per tetramer, have been prepared. Because only Fe porphyrin-containing subunits react with CO, these Fe-Co hybrids are converted to mono-, di-, and tri-CO-ligated states in the presence of CO, respectively, and are proposed to stand as models for mono-, di-, and tri-ligated intermediates of CoHb, respectively. The oxygen binding properties of these Fe-Co hybrids were investigated by measuring oxygen binding isotherms in the presence of CO as a function of pH in the presence and absence of IHP. The ligation of CO to a beta subunit causes larger changes in the oxygen affinity and the Bohr effect than that to an alpha subunit, indicating that the ligation to a beta subunit induces larger affinity-related structural changes in cross-linked CoHb. Di- and tri-CO-ligated intermediates exhibited substantially increased oxygen affinity, reduced Bohr effect, and reduced IHP effect, indicating that they are in high affinity states. Calculation of the Adair equilibrium constants for the first and last oxygenation steps for each of these intermediates permitted the determination of the level of free energy of cooperation. The intermediately ligated species of cross-linked CoHb are distributed in multiple levels of free energy of cooperation within the free energy difference of 1.14 kcal mol-1 between deoxy and fully ligated states of cross-linked CoHb at pH 7.4. The ligation process in CoHb is determined by the number and distribution of the bound ligands, and ligation takes place through steps that require minimal free energy changes.

Cobalt↗
PubMed1993

The porphyrin-iron hybrid hemoglobins. Absence of the Fe-His bonds in one type of subunits favors a deoxy-like structure with low oxygen affinity.

Protoporphyrin-protoheme hybrid hemoglobins (Hb), in which the protohemes (Fe) in either the alpha- or beta-subunits were substituted with protoporphyrins IX (PP) alpha(PP)2 beta(Fe)2 and alpha(Fe)2 beta(PP)2 have been prepared. The structural and functional properties of these hybrid Hbs were investigated by measuring oxygen equilibrium curves and proton nuclear magnetic resonance spectra. The equilibrium constants of the first ligand, K1, observed for alpha(PP)2 beta(Fe)2 were much smaller than K1 values of HbA. The effects of pH and inositol hexaphosphate on K1 were substantially diminished. On the other hand, K1 values of alpha(Fe)2 beta(PP)2 were similar to those of HbA, including the pH and inositol hexaphosphate effects. The deoxy forms of alpha(PP)2 beta(Fe)2 and alpha(Fe)2 beta(PP)2 showed exchangeable proton resonances at 11 and 14 parts/million arising from the hydrogen bonds at the alpha 1 beta 2 contact in a deoxy-like structure. In the liganded form, these signals were dependent upon solution conditions. As K1 became larger, the reduction in the intensity of these signals was observed for both liganded forms. The resonance position of E11 Val originating from the beta subunits of alpha(PP)2 beta(Fe-CO)2 also varied in accordance with K1. We compare properties of PP-Fe hybrids with those of Co-Fe and Ni-Fe hybrids and conclude that the first oxygen binding to the beta heme may be linked to the metal-proximal His interaction in the alpha subunits. However, the first oxygen binding to the alpha heme is linked minimally to the metal-proximal His interaction in the beta subunits but may be correlated instead to the position of E11 Val relative to the porphyrin plane in the beta subunits.

Hemoglobins↗
PubMed1993

Ligand diffusion in the distal heme pocket of myoglobin. A primary determinant of geminate rebinding.

There are at least two picosecond kinetic components in the rebinding of NO to native sperm whale myoglobin. Petrich et al. (Petrich, J. W., Lambry, J.-C., Kuczera, K., Karplus, M., Poyart, C., and Martin, J.-L. (1991) Biochemistry 30, 3975-3987) attribute the slowing of the reaction to a movement of the iron atom out of the plane of the heme following ligand dissociation. In contrast, Gibson et al. (Gibson, Q. H., Regan, R., Elber, R., Olson, J. S., and Carver, T. E. (1992) J. Biol. Chem. 267, 22022-22034) have explained multiphasic geminate reactions by diffusion of NO into the distal heme pocket as determined by its detailed structure. O2 and NO rebinding to iron and cobalt derivatives of native, V68F, and V68I sperm whale myoglobin has been examined. Each iron protein shows a biphasic time course of NO rebinding reactions with widely different rates and amplitudes. Although cobalt does not move out of the plane of the porphyrin on ligand removal, the reactions of the iron and cobalt derivatives of each protein were closely similar. The time course of O2 rebinding to cobalt was also similar to that of NO rebinding to iron. These results are consistent with a primary role for the structure of the distal pocket in determining diffusion of ligands away from the metal atom and as a result the time course of picosecond ligand rebinding.

Animals↗
PubMed1992

Hydrogen bonding to the bound dioxygen in oxy cobaltous myoglobin reduces the superhyperfine coupling to the proximal histidine.

Electron spin echo envelope modulation (ESEEM) spectroscopy was used to study the electron-nuclear coupling in two oxygenated cobalt-substituted hemoproteins, myoglobin (oxyCoMb) and a monomeric hemoglobin from Glycera dibranchiata (oxyCoHbgly). The modulation frequency components in ESEEM spectra of both proteins arose from the coupling to the N epsilon of the proximal histidyl imidazole. The hyperfine and quadrupole coupling parameters for these two nitrogens, calculated by computer spectral simulation, are Aiso = 2.46 MHz, e2qQ = 2.15 MHz, and eta = 0.4 for oxyCoMb and Aiso = 3.70 MHz, e2qQ = 2.70 MHz, and eta = 0.5 for oxyCoHbgly. A hyperfine coupling of 0.6 MHz, found for oxyCoMb in D2O but not for oxyCoHbgly in D2O, was assigned to the coupling to a deuteron that is hydrogen-bonded to the O2 ligand in oxyCoMb. This hydrogen bonding is believed to be responsible for the reduction in hyperfine and nuclear quadrupole coupling to the proximal histidyl imidazole N epsilon in oxyCoMb. A molecular orbital model for O2 adducts of cobaltous compounds [Tovrog et al. (1976) J. Am. Chem. Soc. 98, 5144] was used to understand the hydrogen bond-induced reduction in 14N superhyperfine coupling in oxyCoMb.

Animals↗
PubMed1991

Experimental resolution of cooperative free energies for the ten ligation species of cobalt(II)/iron(II)-CO hemoglobin.

Cooperative free energies have been determined for the 10 ligation species of human hemoglobin in the Co(II)/Fe(II)-CO system. In this system, subunits containing unligated cobaltous hemes coexist in the same tetramer with naturally occurring ferrous hemes that are ligated with carbon monoxide. Tetramers comprising the 10 structurally unique combinations of ligated and unligated subunits were characterized in terms of their dimer-tetramer assembly free energies. By use of the thermodynamic linkage between assembly and ligation, the experimentally resolved values were used to obtain the corresponding cooperative free energies (i.e., the differences between actual free energies of ligation and the summed contributions of intrinsic values). The results obtained are in general accord with previous findings on this same system (Imai et al., 1980). The present study extends this earlier work by resolving the cooperative properties of each configurational isomer of the doubly ligated tetramers. The 10 ligation species were found to distribute into 5 discrete cooperative free energy levels according to a combinatorial code which includes, as a special case, the code found previously with cyanomethemoglobin and manganese-substituted hemoglobin (Smith et al., 1987; Daugherty et al., 1991). This distribution exhibits additional characteristics found in the oxygenation of normal ferrous hemoglobin including the quaternary enhancement effect (Mills & Ackers, 1979a,b). These results, and those of the following paper (Doyle et al., 1991), strongly support the premise that a common set of qualitative rules governs the cooperative interactions in hemoglobin irrespective of

Carbon Monoxide↗
PubMed1991

Light absorption, electron paramagnetic resonance and resonance Raman characteristics of nitridochromium(V) protoporphyrin-IX and its reconstituted hemoproteins.

A surprisingly stable complex of the photolyzed product of azidochromium(III)protoporphyrin-IX was prepared and examined by light absorption, electron paramagnetic resonance (EPR) and resonance Raman spectroscopies. The characteristic EPR spectrum for this complex was consistent with a nitridochromium(V)-porphyrin complex which was two oxidation equivalents above the resting Cr(III) complex. The Cr(V)-N stretching mode was observed at 1010 cm-1 by resonance Raman spectroscopy. A simple diatomic harmonic oscillation model gave a force constant of 6.7 mdyn/A for the Cr(V)-N bond, in the region characteristic for the metal-nitrogen triple bond. Nitridochromium(V) protoporphyrin-IX reconstituted myoglobin and cytochrome c peroxidase were prepared for the first time. The nitridochromium(V)-porphyrins in these apo-proteins were unstable in contrast with the protein-free chromium(V)porphyrin. Upon irradiation of the azide complexes of the chromium(III) protoporphyrin-IX reconstituted myoglobin and cytochrome c peroxidase with ultraviolet light aerobically at room temperature, the characteristic optical and EPR spectra for nitridochromium(V) derivatives were observed. The optical spectra of these photo-induced products were different from those of the nitridochromium(V) protoporphyrin-IX reconstituted hemoproteins. The electrochemical structures of the unusual metalloporphyrin seemed to be modulated by the heme surrounding amino acid residues.

Chromium↗
PubMed1990

Electronic and stereochemical characterizations of the photoinduced intermediates of nitrosyl complexes of metal (S = 5/2)-substituted hemoproteins trapped at low temperature.

Low temperature photolysis of nitric oxide from the nitrosyl complexes of ferric myoglobin (NO-Fe(III)Mb) and manganese(II)-porphyrin-substituted myoglobin (NO-Mn(II)Mb) was examined by electron paramagnetic resonance (EPR) spectroscopy in order to elucidate the electronic and structural natures of the photoinduced intermediates of these hemoprotein-ligand complexes trapped at low temperature. The photoproduct of NO-Fe(III)Mb at 5 K exhibited entirely new X-band EPR absorptions in the magnetic field strength from 0 to 0.4 tesla. The widespread absorption together with distinct, sharp zero-field absorption was consistently observed in the photoproduct of the isoelectronic NO-Mn(II)Mb. These novel ERP signals indicate a spin-coupled pair with an effective spin of S = 2 between the high spin metal center (S = 5/2) and the photodissociated NO (S = 1/2) trapped adjacent to the metal center. On the other hand, the photolyzed form of nitrosyl complexes of Fe(III)- and Mn(II)-Glycera hemoglobins, in which the distal histidine of Mb is replaced by a leucyl residue, exhibited somewhat broader EPR absorptions similar to those of the corresponding native Fe(III)- or unliganded Mn(II)-Glycera hemoglobins, respectively, indicating that the photodissociated NO molecule moved farther away from the metal center in the heme pocket. These observations show the importance of the interaction of the distal residue with the ligand in determining the nature of the photolyzed states.

Animals↗
PubMed1990

Comparative least-squares analysis of hemoglobin oxygen equilibrium curves.

The oxygen-binding properties of hemoglobin have been studied at 600 microM protein concentration with organic phosphate, and analyzed by a series of different nonlinear least-squares analysis methods to determine whether reports of negligibly small values of the third overall Adair parameter, A3, are consequences of the data or a product of the data analysis. Data from other laboratories were analyzed as well. The single most important factor in creating a measurement that yields a small A3 is the use of equally weighted fitting in the Adair equation, while end-weighted fitting generally yields a larger A3. Endpoint extrapolation is ruled out as a major cause of abnormal A3 values. Monte Carlo simulations of the 600 microM results suggest that, if a small A3 were present, end weighting is at least as sensitive to a small A3 as equal weighting. We conclude that equally weighted fitting of the tetrameric Adair equation is unable to resolve the upper asymptote of the oxygen-binding data, resulting in an unusually small value for A3.

Hemoglobin A↗
PubMed1989

Structural characterization of cytochrome c peroxidase by resonance Raman scattering.

Resonance Raman scattering studies are reported on freshly prepared and aged ferric, ligand-free ferrous, and CO-bound ferrous cytochrome c peroxidase. The ferric form of the fresh enzyme has a heme which is penta-coordinate high spin, independent of buffer over the pH range 4.3-7, as determined by well established Raman marker lines. The aged enzyme displays a mixture of spin and coordination states, but it can be stabilized in the penta-coordinate high spin form in the presence of phosphate. These results can be accounted for by considering the size of the channel (6 A wide, 11 A long) between the distal side of the heme and the outer surface of the protein. A phosphate ion may be accommodated in this channel resulting in the stabilization of the distal heme pocket. The ferrous cytochrome c peroxidase in both the ligand-free and CO-bound states has an acidic and an alkaline form. The acidic form has the characteristic spectral features of peroxidases: a high frequency iron-histidine stretching mode (248 cm-1), a high frequency Fe-CO stretching mode (537 cm-1), and a low frequency C-O stretching mode (1922 cm-1). At alkaline pH these frequencies become similar to those of hemoglobin and myoglobin, with the corresponding modes located at 227, 510, and 1948 cm-1, respectively. We attribute the acid/alkaline transition in the ferrous forms of cytochrome c peroxidase to a rearrangement mainly of the proximal side of the heme, culminating in a change of steric interactions between the proximal histidine and the heme or of the hydrogen bonding network involving the proximal histidine. The new data presented here reconcile many inconsistencies reported in the past.

Buffers↗
PubMed1988

Transient kinetics of oxygen dissociation from ferrous subunits of iron-cobalt hybrid hemoglobins. The principal reaction controlling the co-operativity.

The oxygen dissociation constants from Fe subunits in the half-ligated intermediate states of Fe-Co hybrid hemoglobins, alpha(Fe-O2)2 beta(Co)2 and alpha(Co)2 beta(Fe-O2)2, have been determined as functions of pH, temperature and inositol hexaphosphate. The oxygen dissociation rates from alpha(Fe-O2)2 beta(Co)2 are estimated to be more than 1300 s-1 for the deoxy quaternary state (T-state) and less than 3 s-1 for the oxy quaternary state (R-state) at 15 degrees C in 50 mM-Tris or Bis-Tris buffer containing 0.1 M-Cl-, while those of alpha(Co)2 beta(Fe-O2)2 are more than 180 s-1 and less than 5 s-1 for the T and R-states, respectively. The pH dependence of the oxygen dissociation rate from Fe subunits is large enough to be accounted for by the R-T transition, and implies that those half-ligated intermediate hybrids mainly exist in the R-state at pH 8.8, and in the T-state at pH 6.6, while other studies indicated that the half-ligated hybrids are essentially in the R-state at pH 7. Large activation energies of the oxygen dissociation process of 19 to 31 kcal/mol determined from the temperature dependence suggest that the process is entropy-driven.

Animals↗
PubMed1988

Proton nuclear magnetic resonance study of the ferrous derivatives of the dimeric and tetrameric hemoglobin from the mollusc Scapharca inaequivalvis.

Proton NMR spectra have been measured for the two hemoglobins from the mollusc Scapharca inaequivalvis: HbI, a homodimer, and HbII, a heterotetramer. These hemoglobins are endowed with a unique subunit assembly, since the heme carrying E and F helices are involved in the major intersubunit contact. In the far-downfield region of hyperfine-shifted resonances the spectra of HbI and HbII in the deoxy state show respectively one (66.7 ppm) and two (67.8 and 63.6 ppm) exchangeable signals of the proximal histidine N delta H groups, the resonance position being indicative of a significant strain in the iron-imidazole interaction. In the hydrogen-bonded proton region, inter- and intrasubunit hydrogen-bonded proton signals have been detected for both hemoglobins. Deoxy-HbI shows two unique downfield resonances at 11.83 and 11.51 ppm which disappear in the oxygenated state, suggesting that the corresponding hydrogen bonds are involved in the stabilization of the tertiary and/or quaternary structure of the deoxy form. HbII shows even smaller changes in this region upon changes in ligation state. These results therefore provide further proof that, at variance with the vertebrate hemoglobin tetramer, the unique subunit assembly of these proteins is stabilized mainly by hydrophobic interactions.

Animals↗
PubMed1988

Electron paramagnetic resonance study on crosslinked asymmetric Fe(II)-Co(II) hybrids of hemoglobin.

Asymmetric Fe-Co hybrid hemoglobins (Hbs) containing one, two, and three Co(II) protoporphyrins IX per tetramer have been synthesized. These asymmetric Fe-Co hybrids have been prepared by appropriate combinations of subunits of HbA, HbS, Co(II)HbA, Co(II)HbS, and Fe-Co hybrid Hbs and crosslinking with bis(3,5-dibromosalicyl)fumarate, followed by purification with molecular sieve and ion-exchange chromatography. Electron paramagnetic resonance (EPR) spectra have been measured for the crosslinked asymmetric Fe-Co hybrids to investigate the intermediate ligation states of Hb. The electronic state of the Co(II) ion provides a useful probe to estimate how ligation to iron-containing subunits changes the structure of the cobalt-substituted heme vicinity as described previously (T. Inubushi and T. Yonetani (1983) Biochemistry 22, 1894-1900). The crosslink does not affect the EPR spectra of Fe-Co hybrids. EPR spectra of the alpha (Co) subunits in crosslinked hybrids in the fully deoxy state exhibit a mixture of a broad EPR component and a narrow EPR component which correspond to distorted and undistorted Co(II) coordinate states, respectively, and the ratio of the components varies with pH. EPR spectra of the di-liganded asymmetric hybrid, [alpha (Co) beta (Co)]A-[alpha (Fe-CO) beta (Fe-CO)]sXL, and tri-liganded hybrid, [alpha (Co) beta (Fe-CO)]A-[alpha (Fe-CO) beta (Fe-CO)]sXL, show that the coordination state of the alpha (Co) ion in these hybrids is changed to the completely undistorted state in the pH range between 6.5 and 8.8 upon ligation of carbon monoxide (CO). Mono-liganded hybrids, [alpha (Co) beta (Fe-CO)]A-[alpha (Co) beta (Co)]sXL and [alpha (Fe-CO) beta (Co)]A-[alpha (Co) beta (Co)]sXL show intermediate EPR spectra at pH 6.5-7.6, which represent a mixture of the broad and narrow EPR components. The broad component is converted into the narrow one more extensively upon the ligation to the beta (Fe) subunit than to the alpha (Fe) subunit. However, the coordination state of an alpha (Co) subunit in mono-liganded hybrids corresponds to a completely undistorted coordination structure at pH 8.2-8.8. The EPR signal of the alpha (Co) ion is sensitive to the release of alkaline Bohr proton(s) and consequently to the allosteric quaternary structural change of Hb.

Cobalt↗
PubMed1988

The effect of quaternary structure on the kinetics of conformational changes and nanosecond geminate rebinding of carbon monoxide to hemoglobin.

To determine the effect of quaternary structure on the individual kinetic steps in the binding of carbon monoxide to the alpha subunit of hemoglobin, time-resolved absorption spectra were measured after photodissociation of carbon monoxide from a hemoglobin tetramer in which cobalt was substituted for iron in the beta subunits. Cobalt porphyrins do not bind carbon monoxide. Spectra were measured in the Soret region at room temperature after time delays that varied from a few nanoseconds to the completion of ligand rebinding at about 100 ms. The results show that the liganded molecule, alpha(Fe-CO)2 beta(Co)2, is in the R state, but can be almost completely switched into the T state by the allosteric effectors inositol hexaphosphate and bezafibrate. The geminate yield, which is the probability that the ligand rebinds to the heme from within the protein, is found to be 40% for the R state and less than 1% for the T state. According to the simplest kinetic model, these results indicate that carbon monoxide enters the protein in the R and T quaternary conformations at the same rate, and that the 60-fold decrease in the overall binding rate, of carbon monoxide to the alpha subunit in the T state compared to the R state is almost completely accounted for by the decreased probability of binding after the ligand has entered the protein. The results further suggest that the low probability for the T state results from a decreased binding rate to the heme and not from an increased rate of return of the ligand to the solvent.

Allosteric Regulation↗
PubMed1988

The coordination and spin states of yeast cytochrome c peroxidase and their implication to peroxidase mechanism.

Cytochrome c peroxidase, freshly prepared, contains a penta-coordinated heme iron and is fully reactive with hydroperoxides. On the other hand, the enzyme normally stored in frozen states invariably contains different amounts of an altered, aged species whose heme iron is hexa-coordinated. The aged enzyme reacts with hydroperoxides only after a slow conformation change leading to the formation of a reactive penta-coordinated state. Thus, the reactivity of cytochrome c peroxidase with hydroperoxides is strongly controlled by the coordination state of the heme iron. A penta-coordinated heme iron may be a prerequisite for rapid reactions of hydroperoxidases with hydroperoxides.

Binding Sites↗
PubMed1987

A stopped-flow study of the reaction of cytochrome c peroxidase with hydroperoxides.

Transient kinetic measurements show that cytochrome c peroxidase reacts with excess of hydroperoxides to produce compound ES in two phases. The activation energies for the fast and slow phases are calculated to be 6.3 and 20.5 kcal X mol-1, respectively. The fast phase is assigned to the reaction of native active (pulsed) cytochrome c peroxidase with peroxides, whereas the slow phase is due to the presence of an inactive (aged, resting) enzyme. As the active species is exhausted, the equilibrium between the active and inactive enzymes is shifted by a slow conformational change to replenish the active enzyme. Since the rate-limiting step of the reaction of the inactive enzyme with peroxides is the conformation change, the overall reaction rate is independent of the nature and concentration of peroxides.

Cytochrome-c Peroxidase↗
PubMed1987

Yeast cytochrome c peroxidase. Coordination and spin states of heme prosthetic group.

Electronic absorption and electron paramagnetic resonance (EPR) spectroscopic examinations revealed that a freshly prepared cytochrome c peroxidase (CCP) contains a penta-coordinated high spin ferric protoheme group. The penta-coordinated high spin state of fresh CCP is maintained in a remarkably wide range of pH (4-8). The freezing of fresh CCP induces the reversible coordination of an internal strong field ligand to the heme iron to form a hexa-coordinated low spin compound, which shows EPR extrema at gx = 2.70, gy = 2.20 and gz = 1.78. In the presence of glycerol the freezing-induced artifacts are eliminated and the fresh enzyme exhibits an EPR spectrum of rhombically distorted axial symmetry with EPR extrema at gx = 6.4, gy = 5.3, and gz = 1.97 at 10 K, characteristic of the penta-coordinated high spin enzyme. Upon aging CCP is converted to a hexa-coordinated high spin state due to the coordination of an internal weak field ligand to the heme iron. This conversion is accelerated at acidic pH values, and its reversibility varies from fully reversible to irreversible depending on the degree of enzyme aging. The aging-induced hexa-coordinated CCP is unreactive with hydrogen peroxide and exhibits an EPR spectrum of purely axial symmetry with extrema at g = 6 and g = 2 and an electronic absorption spectrum with an intensified Soret band at 408 nm (epsilon 408 nm = 120 mM-1 cm-1) and a blue-shifted charge-transfer band at 620 nm. Spectroscopic properties of different coordination and spin states of fresh and aged CCPs are compiled in order to formulate a generalized spectroscopic characterization of penta- and hexa-coordinated high spin ferric hemoproteins.

Cytochrome-c Peroxidase↗
PubMed1987

Interaction between cytochrome c and cytochrome c peroxidase: excited-state reactions of zinc- and tin-substituted derivatives.

The effect of cytochrome c peroxidase (CCP) and apoCCP on the fluorescence and phosphorescence of Zn and Sn cytochrome c (cyt c) and the effect of cyt c on the fluorescence and phosphorescence of Zn CCP were examined. We found the following: The fluorescence yields of Zn and Sn cyt c were quenched by about 20% by CCP, consistent with energy transfer between the two chromophores with a separation of about 1.8 nm. The phosphorescence spectrum of Zn cyt c (but not Sn cyt c) shifts by 20 nm to the blue upon complexation with either CCP or apoCCP; at the same time the phosphorescence lifetime of Zn cyt c decreases from 12 +/- 2 to 6 ms with apoCCP addition. Zn CCP phosphorescence decay increases from 8.3 to 9.1 ms upon addition of poly(L-lysine) used to mimic cyt c. It is concluded from these results that binding of the redox partner or an analogue to Zn CCP and Zn cyt c results in a conformational change. The respective phosphorescence lifetimes of Zn and Sn cyt c were 13 and 3 ms in the absence of CCP and 1.6 and 1.1 ms in the presence of CCP; this corresponds to a quenching rate due to CCP of 519 and 570 s-1, for Zn and Sn cyt c, respectively. The phosphorescence of Zn CCP is also affected by native cyt c but is dramatically less than the complementary pair; the quenching rate constant is 17 s-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Cytochrome c Group↗