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Author |
Pierce, M.M.; Nall, B.T. |
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Title |
Coupled kinetic traps in cytochrome c folding: His-heme misligation and proline isomerization |
Type |
Journal Article |
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Year |
2000 |
Publication |
Journal of Molecular Biology |
Abbreviated Journal |
J Mol Biol |
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Volume |
298 |
Issue |
5 |
Pages |
955-969 |
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Keywords |
Amino Acid Sequence; Amino Acid Substitution/genetics; Binding Sites; Cytochrome c Group/*chemistry/genetics/*metabolism; *Cytochromes c; Enzyme Stability/drug effects; Fluorescence; Guanidine/pharmacology; Heme/*metabolism; Histidine/genetics/*metabolism; Hydrogen-Ion Concentration; Isomerism; Kinetics; Models, Molecular; Molecular Sequence Data; Mutation/genetics; Proline/*chemistry/metabolism; Protein Conformation/drug effects; Protein Denaturation/drug effects; *Protein Folding; Protein Renaturation; Saccharomyces cerevisiae/enzymology/genetics; Sequence Alignment; Thermodynamics |
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Abstract |
The effect of His-heme misligation on folding has been investigated for a triple mutant of yeast iso-2 cytochrome c (N26H,H33N,H39K iso-2). The variant contains a single misligating His residue at position 26, a location at which His residues are found in several cytochrome c homologues, including horse, tuna, and yeast iso-1. The amplitude for fast phase folding exhibits a strong initial pH dependence. For GdnHCl unfolded protein at an initial pH<5, the observed refolding at final pH 6 is dominated by a fast phase (tau(2f)=20 ms, alpha(2f)=90 %) that represents folding in the absence of misligation. For unfolded protein at initial pH 6, folding at final pH 6 occurs in a fast phase of reduced amplitude (alpha(2f) approximately 20 %) but the same rate (tau(2f)=20 ms), and in two slower phases (tau(m)=6-8 seconds, alpha(m) approximately 45 %; and tau(1b)=16-20 seconds, alpha(1b) approximately 35 %). Double jump experiments show that the initial pH dependence of the folding amplitudes results from a slow pH-dependent equilibrium between fast and slow folding species present in the unfolded protein. The slow equilibrium arises from coupling of the His protonation equilibrium to His-heme misligation and proline isomerization. Specifically, Pro25 is predominantly in trans in the unligated low-pH unfolded protein, but is constrained in a non-native cis isomerization state by His26-heme misligation near neutral pH. Refolding from the misligated unfolded form proceeds slowly due to the large energetic barrier required for proline isomerization and displacement of the misligated His26-heme ligand. |
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Center for Biomolecular Structure, Department of Biochemistry, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA |
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0022-2836 |
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PMID:10801361 |
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no |
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Call Number |
refbase @ user @ |
Serial |
3853 |
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Author |
Saigo, S. |
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Title |
Kinetic and equilibrium studies of alkaline isomerization of vertebrate cytochromes c |
Type |
Journal Article |
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Year |
1981 |
Publication |
Biochimica et Biophysica Acta |
Abbreviated Journal |
Biochim Biophys Acta |
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Volume |
669 |
Issue |
1 |
Pages |
13-20 |
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Keywords |
Amino Acid Sequence; Animals; Cytochrome c Group/*metabolism; Dogs; Hydrogen-Ion Concentration; Isomerism; Kinetics; Vertebrates/metabolism |
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Abstract |
Equilibria and kinetics of alkaline isomerization of seven ferricytochromes c from vertebrates were studied by pH-titration and pH-jump methods in the pH region of 7-12. In the equilibrium behavior, no significant difference was detected among the cytochromes c, whereas marked differences in the kinetic behavior were observed. According to the kinetic behavior of the isomerization, the cytochromes c examined fall into three classes: Group I (horse, sheep, dog and pigeon cytochromes c), Group II (tuna and bonito cytochromes c) and Group III (rhesus monkey cytochrome c). The kinetic results are interpreted in terms of the sequential scheme: Neutral form in equilibrium with fast Transient form in equilibrium with slow Alkaline form where the neutral and alkaline forms are the species stable at neutral and alkaline pH, respectively, and the transient form is a kinetic intermediate. From comparison of the primary sequences of the seven cytochromes c and the classification of these cytochromes c, it is concluded that the amino acid substitution Phe/Tyr at the 46-th position has a major influence on the kinetic behavior. In Group II and III cytochromes c, the ionization of Tyr-46 is suggested to bring about loosening of the heme crevice and thus facilitate the ligand replacement involved in the isomerization. |
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0006-3002 |
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PMID:6271238 |
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Call Number |
refbase @ user @ |
Serial |
3871 |
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Author |
Hasumi, H. |
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Title |
Kinetic studies on isomerization of ferricytochrome c in alkaline and acid pH ranges by the circular dichroism stopped-flow method |
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Journal Article |
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Year |
1980 |
Publication |
Biochimica et Biophysica Acta |
Abbreviated Journal |
Biochim Biophys Acta |
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Volume |
626 |
Issue |
2 |
Pages |
265-276 |
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Keywords |
Circular Dichroism; *Cytochrome c Group; Hydrogen-Ion Concentration; Isomerism; Kinetics; Spectrophotometry |
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Abstract |
The isomerization of horse-heart ferricytochrome c caused by varying pH was kinetically studied by using circular dichroism (CD) and optical absorption stopped-flow techniques. In the pH range of 7--13, the existence of the three different forms of ferricytochrome c (pH less than 10, pH 10--12, and pH greater than 12) was indicated from the statistical difference CD spectra. On the basis of analyses of the stopped-flow traces in the near-ultraviolet and Soret wavelength regions, the isomerization of ferricytochrome c from neutral form to the above three alkaline forms was interpreted as follows (1) below pH 10, the replacement of the intrinsic ligand of methionine residue by lysine residue occurs; (2) between pH 10 and 12, the uncoupling of the polypeptide chain from close proximity of the heme group occurs first, followed by the interconversion of the intrinsic ligands; and (3) above pH 12, hydroxide form of ferricytochrome c is formed, though the replacement of the intrinsic ligand by extrinsic ligands may occur via different routes from those below pH 12. The CD changes at 288 nm and in the Soret region caused by the pH-jump (down) from pH 6.0 to 1.6 were compared with the appearance of the 620-nm absorption band ascribed to the formation of the high-spin form of ferricytochrome c. Both CD and absorption changes indicated that the isomerization at pH 1.6 consisted of two processes: one proceeded within the dead-time (about 2 ms) of the stopped-flow apparatus and the other proceeded at a determinable rate with the apparatus. On the basis of these results, the isomerization of ferricytochrome c at pH 1.6 was explained as follows: (1) the transition from the low-spin form to the high-spin forms occurs within about 2 ms, the dead-time of the stopped-flow apparatus; and (2) the polypeptide chain is unfolded after the formation of the high-spin form. |
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0006-3002 |
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Notes |
PMID:6260152 |
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no |
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Call Number |
refbase @ user @ |
Serial |
3876 |
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Author |
Czerlinski, G.H.; Wagner, M.; Erickson, J.O.; Theorell, H. |
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Title |
Chemical relaxation studies on the system liver alcohol dehydrogenase, NADH and imidazole |
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Journal Article |
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Year |
1975 |
Publication |
Acta Chemica Scandinavica. Series B: Organic Chemistry and Biochemistry |
Abbreviated Journal |
Acta Chem Scand B |
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Volume |
29 |
Issue |
8 |
Pages |
797-810 |
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Keywords |
Alcohol Oxidoreductases/*metabolism; Animals; Computers; Hydrogen-Ion Concentration; Imidazoles/*metabolism; Kinetics; Liver/enzymology/*metabolism; Mathematics; Models, Chemical; NAD/*metabolism; Time Factors |
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Abstract |
Several years ago, Theorell and Czerlinski conducted experiments on the system of horse liver alcohol dehydrogenase, reduced nicotinamide adenine dinucleotide and imidazole, using the first version of the temperature jump apparatus with detection of changes in fluorescence. These early experiments were repeated with improved instrumentation and confirmed the early experiments in general terms. However, the improved detection system allowed to measure a slight concentration dependence of the relaxation time of around 3 ms. Furthermore, the chemical relaxation time was smaller than the one determined earlier (by factor 2). The data were evaluated much more rigorously than before, allowing an appropriate interpretation of the results. The observed relaxation time is largely due to rate constants in an interconversion of ternary complexes, which are faster than three (of the four) dissociation rate constants, determined previously by Theorell and McKinley-McKee.1,2 This fact contributed to earlier difficulties of finding any concentration dependence. However, the binding of imidazole to the binary enzyme-coenzyme complex can be made to couple kinetically into the interconversion rate of the two ternary complexes. The observed signal derives largely from the ternary complex(es). A substantial fluorescence signal change is associated with the observed relaxation process, suggesting a relocation of the imidazole in reference to the nicotinamide moiety of the bound coenzyme. Nine models are considered with two types of coupling of pre-equilibria (none-all). Quantitative evaluations favor the model with two ternary complexes connected by an interconversion outside the four-step (bimolecular) cycle. The ternary complex outside the cycle has much higher fluorescence yield than the one inside. The interconversion equilibrium is near unity for imidazole. If it would be shifted very much to the side of the “dead-end” complex (as in isobutyramide?!), stimulating action could not take place. |
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0302-4369 |
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PMID:882 |
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Call Number |
refbase @ user @ |
Serial |
3887 |
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Author |
Nicol, C.J.; Davidson, H.P.D.; Harris, P.A.; Waters, A.J.; Wilson, A.D. |
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Title |
Study of crib-biting and gastric inflammation and ulceration in young horses |
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Journal Article |
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Year |
2002 |
Publication |
The Veterinary record |
Abbreviated Journal |
Vet. Rec. |
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Volume |
151 |
Issue |
22 |
Pages |
658-662 |
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Keywords |
Animal Husbandry/methods; Animals; Antacids/therapeutic use; *Behavior, Animal; Diet/veterinary; Endoscopy, Gastrointestinal/veterinary; Feces/chemistry; Female; Gastritis/diet therapy/physiopathology/*veterinary; Horse Diseases/diet therapy/*physiopathology/psychology; Horses; Hydrogen-Ion Concentration; Male; Random Allocation; Stereotyped Behavior/*physiology; Stomach Ulcer/diet therapy/physiopathology/*veterinary; Treatment Outcome; Weaning |
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Nineteen young horses that had recently started to perform the stereotypy of crib-biting were compared with 16 non-stereotypic horses for 14 weeks. After initial observations of their behaviour and an endoscopic examination of the condition of their stomachs, the horses were randomly allocated to a control or an antacid diet At the start of the trial, the stomachs of the crib-biting foals were significantly more ulcerated and inflamed than the stomachs of the normal foals. In addition, the faecal pH of the crib-biting foals (6.05) was significantly lower than that of the normal foals (6.58). The antacid diet resulted in a significant improvement in the condition of the horses' stomachs. The crib-biting behaviour declined in most of the foals, regardless of their diet, but tended to decline to a greater extent in the foals on the antacid diet. |
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Department of Clinical Veterinary Science, University of Bristol, Langford House, Bristol BS40 5DU |
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0042-4900 |
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PMID:12498408 |
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Call Number |
refbase @ user @ |
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83 |
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Author |
Ziegler, W.H. |
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[Endocrinological studies in arterial hypertension. Search for phaeochromocytoma] |
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Journal Article |
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Year |
1976 |
Publication |
Schweizerische Medizinische Wochenschrift |
Abbreviated Journal |
Schweiz Med Wochenschr |
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Volume |
106 |
Issue |
34 |
Pages |
1148-1150 |
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Keywords |
Angiography; Blood Volume; Catecholamines/urine; Glucagon/diagnostic use; Histamine/diagnostic use; Humans; Hydrogen-Ion Concentration; Hypertension/*etiology; Methods; Pheochromocytoma/*complications/diagnosis; Tyramine/diagnostic use |
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Elevated urinary catecholamines and their metabolites are the only findings which confirm the presence of pheochromocytoma. This examination is of particular interest if carried out in urine produced after spontaneous hypertensive episodes. Pharmacologic tests when carried out under standard conditions have proven to be a reliable aid in cases of suspected pheochromocytoma. Roentgenographic studies, determination of local plasma catecholamine concentrations and blood volume control should be undertaken in these patients before surgical procedure. |
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German |
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Endokrinologische Untersuchungen bei arterieller Hypertonie. Suche nach Phaochromozytom |
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0036-7672 |
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PMID:12561 |
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Equine Behaviour @ team @ |
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4047 |
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Author |
Rodier, F. |
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Title |
[Spectral properties of porcine plasminogen: study of the acidic transition (author's transl)] |
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Journal Article |
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Year |
1976 |
Publication |
European journal of biochemistry / FEBS |
Abbreviated Journal |
Eur J Biochem |
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Volume |
63 |
Issue |
2 |
Pages |
553-562 |
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Keywords |
Animals; Binding Sites; Guanidines; Hydrogen-Ion Concentration; *Plasminogen; Protein Binding; Protein Conformation; Spectrometry, Fluorescence; Spectrophotometry; Spectrophotometry, Ultraviolet; Swine; Temperature |
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Abstract |
The acidic transition of porcine plasminogen, prepared by affinity chromatography, was studied by non-destructive methods. These methods are based on the analysis of the behaviour of the tryptophyls under various conditions. The perturbation of the absorption and emission spectra by pH or temperature and the dynamic quenching of the intrinsic fluorescence are used to obtain information on structural changes which affect the environment of these residues. It is shown that by decreasing pH the fluorescence emission spectra are shifted toward the long wavelengths, with a broadening of the fluorescence band. The same effect can be obtained at constant pH by heating the protein solution. In order to analyze these phenomena, it is assumed that the fluorescence intensities at 355 nm and 328 nm reflect the proportion of the tryptophans which are exposed to the solvent, and buried, respectively. The plot of the ratio of the fluorescence intensities at these wavelengths versus pH or temperature leads to a titration curve showing an unmasking of tryptophans. The proportion of exposed tryptophans is measured by the dynamic fluorescence quenching technique and the data analyzed according to Lehrer. The plot of the fraction of exposed tryptophyls versus pH also shows the unmasking of these chromophores. Thermal perturbation of a solution of plaminogen at neutral pH induces a difference absorption spectrum whose amplitudes at the maxima are proportional to the number of exposed aromatic residues. The comparison with a solution of fully denatured plasminogen in 6 M guanidium chloride, where all the tryptophyls are exposed, shows that the percentage of exposure is equal to 59%. This number is significantly higher than the percentage found by the fluorescence quenching technique (20%), indicating that some tryptophyls are located in crevices, exposed to the solvent but not to the iodide. At acidic pH the absorption difference spectra induced by thermal perturbation are not classical, since they show an inversion and a new band between 300 nm and 305 nm. This band is mentioned in the literature as a minor band of tryptophan which appears when this chromophore is located in an asymmetric environment. On plotting the maximum amplitude of these spectra obtained at acidic pH versus temperature, we obtain a curve indicating that two types of antagonistic interactions are involved in the perturbation of the chromophores spectra. The spectrophotometric titration of plasminogen gives classical absorption difference spectra. By plotting the maximum amplitude at 292 nm versus pH, we obtain a titration curve with an apparent pK of 2.9 units. This pK is acidic which respect to the pK value of a normal carboxyl. This low value can be due to a positively charged group in the neighbourhood of a carboxyl, which interacts with one or more chromophores. When the carboxyl becomes protonated, this positively charged group is free and available to perturb the environment of some chromophores... |
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French |
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Proprietes spectrales du plasminogene porcin. Etude de la transition acide |
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0014-2956 |
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PMID:4326 |
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Admin @ knut @ |
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22 |
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