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Biomedical subjects

G R Moore

Publications and source records attributed to G R Moore.

At least 145 records · Page 8Linked to original sources

Reactions of mitochondrial cytochrome c with iron-polyaminocarboxylate complexes.

The binding of Fe(III)-polyaminocarboxylate (pac) complexes to mitochondrial ferricytochrome c and ferrocytochrome c has been studied by NMR and four binding sites on cytochrome c have been defined. These sites have different binding preferences for different pac complexes and these are not correlated with the kinetic classification of Wei and Ryan [J. Inorg. Biochem. 17, 237-246 (1982]. It is suggested that the classification of Wei and Ryan is faulty because an assumption made by these authors is incorrect. This assumption is that the reduction of ferricytochrome c by Fe(II)-(pac) complexes proceeds in all cases with similar electron transfer mechanisms with each of the pac complexes having similar self-exchange rates.

Carboxylic Acids↗

Experimental autoimmune encephalomyelitis. Augmentation of demyelination by different myelin lipids.

Alterations in the effect of a known encephalitogenic dose of myelin basic protein (MBP) when inoculated in combination with various myelin lipids have been examined in guinea pigs. A previous study demonstrated that, when MBP was given with galactocerebroside, it produced an acute autoimmune encephalomyelitis similar to that induced by whole white matter in which both inflammation and demyelination were features of the central nervous system lesions. MBP alone, on the other hand, resulted in inflammation only, without demyelination. The present study examined combinations of MBP with the myelin lipids galactocerebroside, sulfatide, ethanolamine phosphoglycerides, and serine phosphoglycerides. The lipids were given with or without MBP, in the same ratio as in intact central nervous system myelin, and were emulsified with complete Freund's adjuvant. An additional group received galactocerebroside and bovine serum albumin in complete Freund's adjuvant. These groups were compared with animals receiving either bovine white matter or MBP in complete Freund's adjuvant. Clinical autoimmune encephalomyelitis was observed in animals receiving bovine white matter, MBP, and all lipid-MBP emulsions; the bovine white matter, galactocerebroside/MBP, sulfatide/MBP, and ethanolamine phosphoglycerides/MBP groups demonstrated central nervous system lesions with a similar picture consisting of inflammation with demyelination, whereas inflammation without demyelination was seen in the MBP and serine phosphoglycerides/MBP groups. Thus, the addition of myelin lipids to MBP leads to the augmentation of demyelination in autoimmune encephalomyelitis lesions in the guinea pig. This might suggest that the immune response against MBP is enhanced by other myelin components. The relevance of these findings to human demyelinating disorders is discussed.

Animals↗

The effect of iron-hexacyanide binding on the determination of redox potentials of cytochromes and copper proteins.

The midpoint redox potentials of Pseudomonas aeruginosa cytochrome c-551 and Rhodopseudomonas viridis cytochrome c2 were measured as a function of pH in the presence of Euglena cytochrome c-558 and the results compared with those obtained in the presence of ferro-ferricyanide. The pattern of pH dependence observed for the two bacterial cytochromes was the same whether it was measured by equilibrium with another redox protein or with the inorganic redox couple. Thus, the pH dependence of redox potential is not a consequence of pH-dependent ligand binding. The midpoint potential of Ps. aeruginosa azurin was measured as a function of pH using both ferro-ferricyanide mixtures and redox equilibrium with horse cytochrome c or Rhodopseudomonas capsulata cytochrome c2. In this case also the pattern of pH dependence obtained did not vary with the redox system used and it closely resembled that of Ps. aeruginosa cytochrome c-551. This is consistent with the observation that the equilibrium between cytochrome c-551 and azurin is relatively independent of pH. An equation was derived which described ph-dependent ligand binding and which can produce theoretical curves to fit the experimental pH dependence of redox potential for both cytochrome and azurin. However, the pronounced effect on such curves produced by varying the ligand association constants, and the insensitivity of the experimental data to changes in ionic strength, suggest that ligand binding effects do not account for the pH dependence of redox potential.

Azurin↗

Batrachotoxin induced axonal necrosis followed by regeneration.

Batrachotoxin (BTX), when applied to peripheral nerve in concentrations sufficient to block impulse transmission and axonal transport, causes axonal necrosis. Quantitation of this phenomenon reveals reduction of both myelinated and unmyelinated fibers 7 days post-BTX injection. Evidence for regeneration correlates with the previously reported recovery of postsynaptic events.

Animals↗

1H-n.m.r. investigation of the interaction between cytochrome c and cytochrome b5.

The interaction between eukaryotic cytochrome c and the tryptic fragment of bovine liver microsomal cytochrome b5 was studied by 1H-n.m.r. spectroscopy, and a procedure was developed that may be generally applicable to the study of macromolecular interactions by n.m.r. At pH6.3 (27 degrees C, I approx. 0.04) the two ferricytochromes were found to form a 1:1 complex with an association constant of approx. 10(3) M -1. The protein--protein-interaction region was found to encompass the region of the surface of horse cytochrome c that includes Ile-81, Phe-82, Ala-83 and Ile-85, and Lys-13 and Lys-72 of horse cytochrome c were suggested to be involved in two important intermolecular interactions. Me3Lys-72 of Candida krusei cytochrome c was shown to be involved in the interaction.

Animals↗

Control of redox properties of cytochrome c by special electrostatic interactions.

An assessment is made of the proposal: electrostatic interactions between the ferric ion of oxidised cytochrome c and its haem propionate sidechains assists in determining the value of the redox potential and plays an important role in the redox state conformation change. Differences between the properties of homologous cytochromes are proposed to be due to differences associated with the charge on their haem propionates.

Animals↗

Ionization of tyrosine and lysine residues in native and modified horse cytochrome c.

1H-n.m.r. and 13C-n.m.r. spectroscopy of horse cytochrome c and 1H-n.m.r. spectroscopy of the lysine-modified proteins N epsilon-acetimidyl-, N epsilon-amidino-, N epsilon-trifluoroacetyl- and N epsilon-maleyl-cytochrome c have shown that, although the lysine modifications do not greatly perturb the protein structure at pH7 and 27 degrees C, at higher temperature or at alkaline pH some parts of the structure are markedly perturbed. At pH7 and 27 degrees C the region of the protein about Ile-57 is affected in all the modified proteins, though not all to the same degree. N epsilon-Maleylation most seriously affects the protein structure, and the fully maleylated protein is readily unfolded. At 27 degrees C all four of the tyrosine residues of native horse cytochrome c have pKa values above 11, but in N epsilon-acetimidyl-cytochrome c the pKa of one tyrosine residue is 10.2.

Animals↗

The conformation of eukaryotic cytochrome c around residues 39, 57, 59 and 74.

1H-n.m.r. studies of horse, tuna, Candida krusei and Saccharomyces cerevisiae cytochromes c showed that each of the proteins contains a similar cluster of residues at the bottom of the protein that assists in shielding the haem from the solvent. The relative positions of the residues forming these clusters vary continuously with temperature, and they change with the change in protein redox state. This conformational heterogeneity is discussed with reference to the conformational flexibility of cytochrome c around residues 57, 59 and 74. Spectroscopic measurements of pKa values for Lys-55 (horse and tuna cytochromes c) and His-33 and His-39 (C. krusei and S. cerevisiae cytochromes c) are in excellent agreement with expectations based on chemical-modification studies of horse cytochrome c. [Bosshard & Zürrer (1980) J. Biol. Chem. 255, 6694-6699] and on the X-ray-crystallographic structure of tuna cytochrome c [Takano & Dickerson (1981) J. Mol. Biol. 153, 79-94, 95-115].

Animals↗

Structural role of the tyrosine residues of cytochrome c.

The tertiary structures of horse, tuna, Neurospora crassa, horse [Hse65,Leu67]- and horse [Hse65,Leu74]-cytochromes c were studied with high-resolution 1H n.m.r. spectroscopy. The amino acid sequences of these proteins differ at position 46, which is occupied by phenylalanine in the horse proteins but by tyrosine in the remaining two, and at positions 67, 74 and 97, which are all occupied by tyrosine residues in horse and tuna cytochrome c but in the other proteins are substituted by phenylalanine or leucine, though there is only one such substitution per protein. The various aromatic-amino-acid substitutions do not seriously affect the protein structure.

Amino Acid Sequence↗

1H NMR studies of the electron exchange between cytochrome c and iron hexacyanides. Definition of the iron hexacyanide binding sites on cytochrome c.

Binding of [Fe(CN)6]3-, [Cr(CN)6]3-, [Co(CN)6]3- and [Cr(C2O4)3]3- to horse, tuna and Candida krusei cytochromes c has been studied by high-resolution 1H NMR spectroscopy. All the reagents bind at the same sites. There are at least two binding sites, and probably three, on horse cytochrome c at pH 7. One of the sites is only a weak binding site and is far from the haem group, whereas the other site(s) is(are) at the haem crevice. Ka for binding of [Fe(CN)6]3- to trimethyllysine-72 of C. krusei ferricytochrome c is 140 +/- 15 M-1 at 27 degrees C and pH 7.

Animals↗

1H NMR studies of eukaryotic cytochrome c. Resonance assignments and iron-hexacyanide-mediated electron exchange.

1H NMR resonance assignments in the spectra of horse, tuna, Neurospora crassa and Candida krusei cytochromes c are described. Assignments have been made using NMR double-resonance techniques in conjunction with electron-exchange experiments, spectral comparison of related proteins, and consideration of the X-ray structure of tuna cytochrome c. Resonances arising from 11 residues of horse cytochrome c have been assigned.

Animals↗

The binding of platinum complexes to tuna cytochrome c.

The binding of [PtCl4]2- and cis-[PtCl2(NH3)2] to methionine-65 of tuna cytochrome c was investigated by 1H n.m.r. The modification at methionine-65 is shown to cause an extremely small structural perturbation to the protein at the site of modification.

Animals↗

Metal coordination centres of class II cytochromes c.

The class II cytochromes Rhodospirillum molischianum cytochrome c', Rhodopseudomonas palustris cytochrome C556 and Agrobacterium tumefaciens (B2a) cytochrome c556 have been investigated with a variety of spectroscopic techniques. The cytochrome c' was found to be high-spin and the two cytochromes c556 were found to be mainly low-spin and sx-coordinate with the fifth and sixth ligands being histidine and methionine. The implications of the different types of iron coordination are discussed.

Cytochrome c Group↗

NMR redox studies of Desulfovibrio vulgaris Cytochrome c3. Electron transfer mechanisms.

The 300-MHz proton NMR spectra of the tetrahaem cytochrome c3 from Desulfovibrio vulgaris were examined while varying the pH and the redox potential. The analysis of the complete NMR reoxidation pattern was done taking into account all the 16 redox states that can be present in the redox titration of a tetra-redox-center molecule. A network of saturation transfer experiments performed at different oxidation stages, between the fully reduced and the fully oxidized states, allowed the observation of different resonances for some of the haem methyl groups. In the present experimental conditions, some of the haems show a fast intramolecular electron exchange rate, but the intermolecular electron exchange is always slow. In intermediate reoxidation stages, large shifts of the resonances of some haem methyl groups were observed upon changing the pH. These shifts are discussed in terms of a pH dependence of the haem midpoint redox potentials. The physiological relevance of this pH dependence is discussed.

Chemical Phenomena↗

Batrachotoxin induced axonal necrosis in peripheral nerves.

Batrachotoxin (BTX) depolarizes electrogenic membranes and also blocks axonal transport. We demonstrate that when applied in doses sufficient to block impulse transmission and axonal transport, BTX induces axonal necorsis. It is postulated that axonal necrosis is secondary to influx of sodium ions and water.

Animals↗