351
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Sarti P, Antonini G, Malatesta F, Vallone B, Villaschi S, Brunori M, Hider RC, Hamed K. Reconstitution of cytochrome c oxidase in phospholipid vesicles containing polyvinylic polymers. Biochem J 1989; 257:783-7. [PMID: 2539096 PMCID: PMC1135656 DOI: 10.1042/bj2570783] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Cytochrome c oxidase was reconstituted in phospholipid vesicles in the presence of highly hydrophobic poly(vinyl alkanoate) polymers. Electron-microscopy observations demonstrated that polymer interaction with the lipid phase induces vesicles to adopt smaller diameters than those typical of standard proteoliposomes. Functional characterization of these polymer-proteoliposome structures indicates that the reconstitution of the enzyme proceeds efficiently without causing either scrambling of the protein orientation in the membrane or loss of respiratory control. A clear dependence of respiratory control ratio on vesicle size was also demonstrated, which is in agreement with a previous model proposed for control of activity of cytochrome c oxidase vesicles [Brunori, Sarti, Colosimo, Antonini, Malatesta, Jones & Wilson (1985) EMBO J. 4, 2365-2368].
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352
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Condò SG, Bellelli A, Brunori M, Corda M, Pellegrini MG, Clementi EM, Giardina B. The functional properties of amphibian hemoglobin: The case of Salamander salamander and Hydromantes genei. ACTA ACUST UNITED AC 1989. [DOI: 10.1016/0300-9629(89)90044-3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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353
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Antonini G, Malatesta F, Sarti P, Vallone B, Brunori M. ATP-induced spectral changes in cytochrome c oxidase. A kinetic investigation. Biochem J 1988; 256:835-40. [PMID: 2852006 PMCID: PMC1135491 DOI: 10.1042/bj2560835] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Mixing ATP with soluble oxidized cytochrome c oxidase induces a spectral perturbation in the Soret region of the enzyme. This spectral perturbation is observed at ATP concentrations similar to those found to modulate the catalytic activity of cytochrome c oxidase [Malatesta, Antonini, Sarti & Brunori (1987) Biochem. J. 248, 161-165]. The process is reversible and corresponds to a simple binding with Kd = 0.2 mM at 25 degrees C. The absorbance change follows a first-order time course, and analysis of the ATP-concentration-dependence indicates the presence of a rate-limiting monomolecular step that governs the process. From the temperature-dependence of this process, studied at saturating concentrations of ATP, an activation energy of 44 kJ/mol (10.6 kcal/mol) was measured. The spectral perturbation also occurs when cytochrome c oxidase is reconstituted into artificial phospholipid vesicles, with equilibria and kinetics similar to those observed with the soluble enzyme. Mixing ATP with soluble oxidized cyanide-bound cytochrome c oxidase induces a different spectral perturbation, and the apparent affinity of ATP for the enzyme is substantially increased. There is no absolute specificity for ATP, because EGTA, inositol hexakisphosphate, sulphate and phosphate are all able to induce an identical spectral perturbation with the same kinetics, although the value of the apparent Kd is different for the various anions. The presence of Mg2+ ions decreases, in a saturation-dependent fashion, the apparent affinity of cytochrome c oxidase for ATP. The absorbance change can be correlated to the displacement of the Ca2+ bound to cytochrome c oxidase.
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354
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Coletta M, Ascenzi P, Brunori M. Kinetic evidence for a role of heme geometry on the modulation of carbon monoxide reactivity in human hemoglobin. J Biol Chem 1988; 263:18286-9. [PMID: 3192534] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Kinetics of CO binding to human hemoglobin (Hb) has been followed below neutrality. With respect to the behavior observed at pH 7.0, CO binding to deoxy-Hb at pH 2.3 displays a much faster second-order combination rate constant (1.2 x 10(-7) M-1 s-1) and loss of the autocatalytic character of the kinetic progress curve. The spectroscopic features of the transient deoxy-Hb at pH 2.75 indicate the phenomenon to be related to the cleavage of the proximal histidine N epsilon-Fe bond, as reported for monomeric hemoproteins (Coletta, M., Ascenzi, P., Traylor, T. G., and Brunori, M. (1985) J. Biol. Chem. 260, 4151-4155). The faster CO binding rate constant, higher than that characteristic of the R state, cannot be attributed to either (i) an enhanced dimerization of deoxy-Hb at low pH, or (ii) a quaternary switch of the unliganded form to the R0 state. The data indicate that interaction(s) of the heme on the proximal side is crucial in accounting for the difference in the CO binding rate constant between the two quaternary conformations of hemoglobin.
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355
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Sarti P, Antonini G, Malatesta F, Vallone B, Brunori M. Is the internal electron transfer the rate-limiting step in the catalytic cycle of cytochrome c oxidase? Ann N Y Acad Sci 1988; 550:161-6. [PMID: 2854388 DOI: 10.1111/j.1749-6632.1988.tb35332.x] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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356
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Antonini G, Malatesta F, Sarti P, Vallone B, Brunori M. ATP-induced spectral perturbation in cytochrome oxidase. Kinetic aspects and role of calcium ions. Ann N Y Acad Sci 1988; 550:118-23. [PMID: 2854383 DOI: 10.1111/j.1749-6632.1988.tb35328.x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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357
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Malatesta F, Antonini G, Sarti P, Vallone B, Brunori M. Modulation of cytochrome c oxidase activity by an electrical transmembrane gradient. Ann N Y Acad Sci 1988; 550:269-76. [PMID: 2854399 DOI: 10.1111/j.1749-6632.1988.tb35342.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
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358
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Bellelli A, Benedetti PL, Coletta M, Ippoliti R, Brunori M. Human erythrocytes cross-linked with glutaraldehyde general properties and significance as a blood substitute. Biochem Biophys Res Commun 1988; 156:970-7. [PMID: 3142468 DOI: 10.1016/s0006-291x(88)80939-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Human erythrocytes extensively crosslinked with glutaraldhyde display very high mechanical and chemical resistance, but still bind oxygen reversibly. Depending on the initial reaction conditions the oxygen affinity of fixed erythrocytes is either high or (partially) low, the binding curve being always non cooperative. Cells which are extensively crosslinked but still active may find a number of biotechnological applications; fixed erythrocytes may (for example) be investigated as possible blood substitutes.
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359
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Bertollini A, Santucci R, Amiconi G, Ascoli F, Currell DL, Mursal O, Brunori M. Multiplicity of interactions between dromedary hemoglobin and solvent components. A structural and functional study. EUROPEAN JOURNAL OF BIOCHEMISTRY 1988; 176:669-73. [PMID: 3169019 DOI: 10.1111/j.1432-1033.1988.tb14329.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The interaction of dromedary hemoglobin with various solvent components [2-(p-chlorophenoxy)-2-methylpropionic acid (CFA), 2,3-bisphospho-D-glycerate (glycerate-2,3-P2) and chloride] has been studied. 1. CFA greatly lowers the oxygen affinity of dromedary hemoglobin. 2. The oxygen-linked CFA binding sites are probably located in the deoxy derivative at the alpha cleft, while in the oxy form and in the presence of two other effectors (glycerate-2,3-P2 and chloride) additional, structurally and possibly functionally relevant binding site(s) should be considered. 3. Both CFA and glycerate-2,3-P2 stabilize the deoxy-like tertiary structure in the oxy derivative. 4. Chloride appears to be fundamental to obtain quaternary structural changes. 5. Interaction energy, retained in the protein when the three ligands (CFA, glycerate-2,3-P2 and chloride) are bound to the oxy form, favours intermediates not stable if only one or two allosteric effector(s) is (are) present on the protein. 6. The oxygen affinity appears to be related to both tertiary and quaternary structural changes, while cooperatively is largely invariant with solvent conditions. In conclusion, the functional properties of dromedary hemoglobin do not depend in any simple way on the variety of stabilized conformations.
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360
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Coletta M, Amiconi G, Bellelli A, Bertollini A, Carsky J, Castagnola M, Condò S, Brunori M. Alteration of T-state binding properties of naturally glycated hemoglobin, HbA1c. J Mol Biol 1988; 203:233-9. [PMID: 3184188 DOI: 10.1016/0022-2836(88)90104-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The thermodynamic and kinetic properties of the most abundant glycated hemoglobin in human blood, HbA1c, have been studied in detail. They display significant differences as compared to normal hemoglobin, HbA0, in that (1) the shape of the oxygen binding curve of HbA1c in the Hill plot is markedly asymmetrical, with a lower asymptote extending up to approximately 40% oxygen saturation, and the oxygen affinity of the T state being tenfold higher than in HbA0; (2) oxygen pulse experiments on HbA1c show a slower rate of ligand dissociation (k = 25 s-1) even at low levels of oxygen saturation, where the T state is largely predominant; (3) kinetics of CO combination to deoxy HbA1c followed by means of stopped-flow experiments reveal the presence of a quickly reacting component, whose fraction increases upon dilution of hemoglobin. These results show that in contrast to what has been stated by other authors, HbA1c displays functional properties markedly different from HbA0. Analysis indicates that glycation of human hemoglobin affects the T quaternary structure, bringing about a more "relaxed" T state and leading to preferential binding to one type of chain (which is unaffected by chloride ions).
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361
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Ascenzi P, Desideri A, Amiconi G, Bertollini A, Bolognesi M, Castagnola M, Coletta M, Brunori M. Effect of inositol hexakisphosphate on the spectroscopic properties of the nitric oxide derivative of ferrous naturally glycated human hemoglobin HbA1c. J Inorg Biochem 1988; 34:19-24. [PMID: 2851030 DOI: 10.1016/0162-0134(88)85014-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The effect of inositol hexakisphosphate (IHP) on the spectroscopic (EPR and absorbance) properties of the nitric oxide derivative of ferrous naturally glycated human hemoglobin HbA1c (HbA1cNO) has been investigated quantitatively. The results obtained show that 1) both in the absence and presence of IHP, the EPR and absorbance spectra of HbA1cNO show the same basic characteristics described for the nitrosyl derivative of ferrous HbA0, the nonglycated major component of human hemoglobin (HbA0NO); and 2) HbA1cNO binds IHP with an apparent dissociation equilibrium constant (upsilon = 1.8 x 10(-2) M), which is at least four orders of magnitude higher than that estimated for the polyphosphate interaction with HbA0NO (less than or equal to 3 x 10(-6) M). These data provide further independent evidence that interaction(s) of polyphosphates at the specific cleft between beta-chains along the dyad-axis is sterically hindered in HbA1c by the presence of the two glucose residues covalently bound to the N-termini of beta-chains, this finding being in agreement with the reduced effect of polyanions on HbA1c spectral and ligand-binding properties.
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362
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Coletta M, Alayash AI, Wilson MT, Benedetti PA, Evangelista V, Brunori M. Single cell microspectroscopy reveals that erythrocytes containing hemoglobin S retain a 'memory' of previous sickling cycles. FEBS Lett 1988; 236:127-31. [PMID: 3402610 DOI: 10.1016/0014-5793(88)80299-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Red blood cells from patients homozygotes for hemoglobin S (HbS) have been studied using a computer-controlled microspectrophotometer, which allows measurements of spectra and dynamics to be undertaken in a single erythrocyte. Complete photodissociation of HbCO results in polymerization of intracellular deoxyhemoglobin S and deformation of the cell. This is associated with a delayed optical change, which, for the same cell, was found to be highly reproducible between repeated cycles of sickling. Comparison of photographic records and absorbance time courses indicates that an erythrocyte, once having undergone a photochemically induced sickling event, always deforms along the same axis during subsequent cycles. This behaviour implies that the cell retains a 'memory' of its previous cycle(s), possibly via slow relaxations of the membrane. In addition, rebinding of CO to intracellular hemoglobin was found to be slower if measured after deformation of the cell, with possible important implications for the pathological mechanism of sickling.
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363
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364
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De Sanctis G, Falcioni G, Giardina B, Ascoli F, Brunori M. Mini-myoglobin. The structural significance of haem-ligand interactions. J Mol Biol 1988; 200:725-33. [PMID: 3411608 DOI: 10.1016/0022-2836(88)90483-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The properties of purified mini-myoglobin, the fragment 32-139 of horse heart myoglobin reconstituted with protohaem, have been investigated from a structural and functional view point. The recovery of secondary structure observed in the carbon monoxide derivative of mini-myoglobin, as shown by circular dichroism, and the overall similarity of the haem pocket to that of myoglobin, as deduced from the fluorescence properties of the complex with 1-anilino-8-naphthalene sulphonate, indicate that, in the presence of the constraints imposed by the haem and its ligands, the miniprotein reacquires a conformation close to that of native myoglobin. These spectroscopic data parallel the conclusions drawn from the results of ligand combination and dissociation kinetics; stopped-flow experiments indicate that carbon monoxide and oxygen bind to mini-myoglobin with rates almost identical with those of myoglobin itself. The significance of mini-myoglobin as a model of an oxygen-carrying protein, with some of the expected functional characteristics of an ancestor haemoprotein, is discussed, with reference to the mosaic structure of the myoglobin gene and the role of different exons in the evolution of proteins.
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365
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Brunori M, Malatesta F. Biochemistry, Bioenergetics and Clinical Applications of Ubiquinol. J Electroanal Chem (Lausanne) 1988. [DOI: 10.1016/0022-0728(88)87134-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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366
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Di Prisco G, Giardina B, D'Avino R, Condò SG, Bellelli A, Brunori M. Antarctic fish hemoglobin: an outline of the molecular structure and oxygen binding properties—II. Oxygen binding properties. ACTA ACUST UNITED AC 1988. [DOI: 10.1016/0305-0491(88)90299-4] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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367
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Brunori M, Antonini G, Malatesta F, Sarti P, Wilson MT. Cytochrome-c oxidase. Subunit structure and proton pumping. EUROPEAN JOURNAL OF BIOCHEMISTRY 1987; 169:1-8. [PMID: 2445564 DOI: 10.1111/j.1432-1033.1987.tb13572.x] [Citation(s) in RCA: 89] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
This article reviews the significance of the subunit structure of cytochrome-c oxidase in proton pumping and in particular summarizes available evidences for or against a role of subunit III in the control of this important function of the enzyme.
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368
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Malatesta F, Antonini G, Sarti P, Brunori M. Modulation of cytochrome oxidase activity by inorganic and organic phosphate. Biochem J 1987; 248:161-5. [PMID: 2829818 PMCID: PMC1148513 DOI: 10.1042/bj2480161] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
The activity of cytochrome oxidase reconstituted into phospholipid vesicles has been studied as a function of orthophosphate, ATP and inositol hexakisphosphate concentrations. The respiratory-control ratio was found to be quite sensitive to these compounds and was inversely related to the anion concentration. This effect is related to a phosphate-dependent decrease in the rate constant for ferrocytochrome c oxidation observed in the presence of ionophores. The data cannot be interpreted simply on the basis of ionic strength, which is known to limit cytochrome c binding to cytochrome oxidase, since cytochrome oxidase-containing vesicles responded differently to phosphate depending on the energization state of the phospholipid membrane.
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369
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Condò SG, Giardina B, Bellelli A, Brunori M. Xenopus laevis hemoglobin and its hybrids with hemoglobin A+. Biochemistry 1987; 26:6718-22. [PMID: 3427040 DOI: 10.1021/bi00395a022] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Isolated alpha and beta chains from Xenopus laevis hemoglobin have been purified. The isolation procedure yields native alpha chains whose functional behavior has been characterized and compared with that of human alpha chains. Isolated beta chains in the presence of oxygen are characterized by low stability, and hence their functional characterization was limited to the CO binding kinetics. When stoichiometric amounts of the isolated alpha and beta chains are mixed, a tetramer characterized by heme-heme interactions and oxygen affinity comparable to that of the native molecule is readily reconstituted. Moreover, both chains, under appropriate conditions, form stable hybrid tetramers with the partner subunits from human hemoglobin; results on the functional properties of these hybrid hemoglobins are presented and discussed in relation to the stereochemical model of the Root effect.
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370
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Coletta M, Santucci R, Focesi A, Ascoli F, Brunori M. Redox properties of components I and IV of trout hemoglobins: kinetic and potentiometric studies. BIOCHIMICA ET BIOPHYSICA ACTA 1987; 915:415-9. [PMID: 3651480 DOI: 10.1016/0167-4838(87)90028-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Redox properties of component I and IV from trout hemoglobin (Salmo irideus) have been studied kinetically and at equilibrium. In the case of component I of trout hemoglobin, the mid-point potential (Eh) is pH independent below the acid-alkaline transition (pKa approximately equal to 8.6) and decreases at higher pH, following the deprotonation of the water molecule. Similarly to human hemoglobin, the mid-point potential of component IV of trout hemoglobin is pH-dependent, but the redox Bohr effect is extended to more acid pH. Moreover, the cooperativity of the redox equilibrium process is higher than in human hemoglobin. These features parallel the oxygen-binding properties of the same hemoglobin components from trout hemolysate. Differently from human hemoglobin, the oxidation kinetics of the two hemoglobins from trout by potassium ferricyanide show markedly biphasic progress curves with pH-independent second-order rate constants. This behavior suggests a different energy barrier for the interaction with ferricyanide in the two types of subunit of both Hb components from trout.
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371
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Bellelli A, Foon R, Ascoli F, Brunori M. Haem disorder in two myoglobins: comparison of reorientation rate. Biochem J 1987; 246:787-9. [PMID: 3689333 PMCID: PMC1148347 DOI: 10.1042/bj2460787] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The globins from sperm whale and from Aplysia limacina myoglobins were reconstituted by addition of stoichiometric ferric protohaem and the Soret c.d. was followed as a function of time. For both reconstituted proteins, the Soret c.d. changes with time, reflecting haem reorientation inside its pocket, as previously described [Aojula, Wilson & Drake (1986) Biochem. J. 237, 613-616] for sperm whale myoglobin. The time course of the c.d. transition is found to be approx. 10 times faster in Aplysia than in sperm whale myoglobin, a result which is in agreement with the known structural and physicochemical properties of the two myoglobins; furthermore, these results confirm that c.d. and n.m.r. data on haem orientation in haemoproteins reflect the same molecular phenomenon.
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372
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Falcioni G, Cincolà G, Brunori M. Glutathione peroxidase and oxidative hemolysis in trout red blood cells. FEBS Lett 1987; 221:355-8. [PMID: 3622774 DOI: 10.1016/0014-5793(87)80955-9] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Red blood cells from the trout Salmo irideus contain several hemoglobin components that are prone to oxidation with production of oxygen radicals. The rate of hemolysis has been correlated to the extent of methemoglobin formation. A difference in the rate of hemolysis between red blood cells saturated with either CO or O2 was evident only when diminished glutathione peroxidase activity was observed. These results confirm the important role of this enzyme in providing protection against or repair of oxidative damage to the red cell membrane.
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373
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Abstract
The reaction of Xenopus hemoglobin with oxygen and carbon monoxide has been reinvestigated over the pH range 8.5-6.0, in the absence and presence of organic phosphates (2,3-diphosphoglycerate or inositol hexakisphosphate), to establish if the tetramer can be stabilized in a T-quaternary state by protons and polyphosphate; the equilibrium and kinetic data indicate that Xenopus hemoglobin does exhibit a Root effect. These new results are discussed with reference to those reported by Bridges et al. [(1985) Resp. Physiol. 61, 125-136] on Xenopus blood and, more generally, to the molecular definition and the structural basis of the Root effect as an extreme form of the Bohr effect.
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374
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Santucci R, Brunori M, Ascoli F. Unfolding and flexibility in hemoproteins shown in the case of carboxymethylated cytochrome c. BIOCHIMICA ET BIOPHYSICA ACTA 1987; 914:185-9. [PMID: 3038191 DOI: 10.1016/0167-4838(87)90062-8] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
A circular dichroism study of carboxymethylated cytochrome c has been performed to obtain further information on the structural basis responsible for the observed changes in ligand binding and redox properties of the modified cytochrome c. The results give additional evidence of local structural changes occurring in the heme environment upon rupture of the (Met-80)-heme iron bond in the modified protein. This produces no alterations of the overall molecular conformation, but results in drastic changes in redox potential. In addition, analysis of the reversible conformational transitions induced by urea in the native and the modified proteins supports the idea that the modified derivative can be considered as an 'intermediate state' between the native and the fully unfolded protein.
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375
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Antonini G, Brunori M, Malatesta F, Sarti P, Wilson MT. Reconstitution of monomeric cytochrome c oxidase into phospholipid vesicles yields functionally interacting cytochrome aa3 units. J Biol Chem 1987; 262:10077-9. [PMID: 3038866] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
When the carbon monoxide complex of fully reduced cytochrome c oxidase, reconstituted into liposomes, is mixed with oxygen-containing buffer, complex kinetic progress curves are observed. This pattern is seen irrespective of whether the oxidase used in reconstitution is the dimeric or monomeric (subunit III-depleted) enzyme. These findings are interpreted in the light of similar experiments on the detergent-solubilized enzyme reported by Gibson and Greenwood (Gibson, Q.H., and Greenwood, C. (1963) Biochem. J. 86, 541-554) and confirmed by ourselves. We conclude that reconstitution of monomeric (subunit III-less) enzyme yields, preferentially, vesicles containing more than one functional unit, possibly associated as dimers. This result is of significance to our understanding of the relationships between aggregation state and proton pumping capacity of cytochrome oxidase.
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