An intramolecular electron-transfer process has previously been shown to take place between the Cys3 - Cys26 radical-ion (RSSR-) produced pulse radiolytically and the Cu(II) ion in the blue single... Show moreAn intramolecular electron-transfer process has previously been shown to take place between the Cys3 - Cys26 radical-ion (RSSR-) produced pulse radiolytically and the Cu(II) ion in the blue single-copper protein, azurin [Farver, O. & Pecht, I. (1989) Proc. Natl Acad Sci. USA 86, 6868 - 6972]. To further investigate the nature of this long-range electron transfer (LRET) proceeding within the protein matrix, we have now investigated it in two azurins where amino acids have been substituted by single-site mutation of the wild-type Pseudomonas aeruginosa azurin. In one mutated protein, a methionine residue (Met44) that is proximal to the copper coordination sphere has been replaced by a positively charged lysyl residue ([M44K]azurin), while in the second mutant, another residue neighbouring the Cu-coordination site (His35) has been replaced by a glutamine ([H35Q]azurin). Though both these substitutions are not in the microenvironment separating the electron donor and acceptor, they were expected to affect the LRET rate because of their effect on the redox potential of the copper site and thus on the driving force of the reaction, as well as on the reorganization energies of the copper site.The rate of intramolecular electron transfer from RSSR - to Cu(II) in the wild-type P. aeruginosa azurin (DELTAG-degrees = -68.9 kJ/mol) has previously been determined to be 44 +/- 7 s-1 at 298 K, pH 7.0. The [M44K]azurin mutant (DELTAG-degrees = - 75.3 kJ/mol) was now found to react considerably faster (k = 134 +/- 12 s-1 at 298 K, pH 7.0) while the [H35Q]azurin mutant (DELTAG-degrees = - 65.4 kJ/mol) exhibits, within experimental error, the same specific rate (k = 52 +/- 11 s-1 298 K, pH 7.0) as that of the wild-type azurin. From the temperature dependence of these LRET rates the following activation parameters were calculated: DELTAH double dagger = 3 7.9 +/- 1.3 kJ/mol and 47.2 +/- 0.7 kJ/mol and DELTAS double dagger = - 86.5 +/- 5.8 J/mol . K and - 46.4 +/- 4.4 J/mol . K for [H35Q]azurin and [M44K]azurin, respectively. Using the Marcus relation for intramolecular electron transfer and the above parameters we have determined the reorganization energy, lambda and electronic coupling factor, beta. The calculated values fit very well with a through-bond LRET mechanism. Show less
Ab-initio calculations at the UHF and CASSCF levels have been performed in which the geometry of pyrimidine in the B-3(1)(npi*), 3A2(npi*), and 3A1(pipi*) states has been optimized. The... Show moreAb-initio calculations at the UHF and CASSCF levels have been performed in which the geometry of pyrimidine in the B-3(1)(npi*), 3A2(npi*), and 3A1(pipi*) states has been optimized. The calculations clearly demonstrate the influence of vibronic coupling on the molecular and electronic structure of the molecule in these states. For the npi* states, conformations corresponding to minimum energy are found that deviate significantly from planar. For the 3A1(pipi*) state, vibronic coupling similar to that between the B-3(1u) and 3E1u states of benzene has been found. From the calculations, we deduce a dynamic out-of-plane distortion of the molecule in the B-3(1u)(npi*) state, which provides for a coherent description of the results of optical and magnetic-resonance data available for the lowest triplet state of pyrimidine. The out-of-plane distortions occurring in the B-3(1)(npi*) and 3A2(npi*) states conform to the increased antibonding character of the pi-electron system upon npi* excitation. Show less
Het jaarplan 1993 van de Rotterdamse politie heeft beroering gebracht in de kalme wateren van het drugsbeleid. De Rotterdamse politie stijgt het water wellicht tot aan de lippen op het gebied van... Show moreHet jaarplan 1993 van de Rotterdamse politie heeft beroering gebracht in de kalme wateren van het drugsbeleid. De Rotterdamse politie stijgt het water wellicht tot aan de lippen op het gebied van de openbare orde. De overheid moet volgens hen als gratis afhaalchinees gezien worden. Een plek waar de zware drugsverslaafden een stempel op hun stempelkaart krijgen als bewijs van ontvangst. Waarna zij dan heerlijk op de hoek van de straat naar hartelust kunnen chinezen (na verhitting inhaleren van de heroïne-dampen vanaf aluminiumfolie). Show less
Met de Wet Persoonsregistratie probeert Big Brother (de overheid) de privacy van ''us" (de burgers) te beschermen. Hieronder volgt een korte beschouwing van het al dan niet werken... Show moreMet de Wet Persoonsregistratie probeert Big Brother (de overheid) de privacy van ''us" (de burgers) te beschermen. Hieronder volgt een korte beschouwing van het al dan niet werken van de wet en de bijzondere positie van de bevolkingsadministratie. Show less
Het lijkt in te zijn tegenwoordig: ontsnappen uit zwaar bewaakte gevangenissen. Als ware professionals gebruiken de inmates de spectaculairste middelen en weten de heren Gevangenisdirecteuren zich... Show moreHet lijkt in te zijn tegenwoordig: ontsnappen uit zwaar bewaakte gevangenissen. Als ware professionals gebruiken de inmates de spectaculairste middelen en weten de heren Gevangenisdirecteuren zich steeds weer geconfronteerd met de "boze buitenwereld". De nood is de vader aller commissies. Helaas blijkt hij maar al te vruchtbaar. Als een ware Athena ontsprong de commissie Hoekstra aan het brein van Kosto. Show less
De kop van dit artikel luidt "Scheiden doet leiden". Lees verder om er achter te komen of dit een goede benaming is of dat er beter "Scheiden doet lijden" had kunnen staan!
Al direct vanaf de wieg word je geconfronteerd met de overheid en zelfs na de dood laat die overheid je niet met rust. Wellicht moet je de hemelse paden betreden zonder nier, hart of lever om... Show moreAl direct vanaf de wieg word je geconfronteerd met de overheid en zelfs na de dood laat die overheid je niet met rust. Wellicht moet je de hemelse paden betreden zonder nier, hart of lever om andere mensen beneden te houden. Orgaandonaties verkeren nog steeds in de sociale en ethische nevel van de taboesfeer. Vandaar dat er een tekort bestaat aan orgaandonoren, wat mensenlevens kost. De overheid wil dan ook niet passief toekijken. Er ligt een wetsvoorstel in de Tweede Kamer, dat de huidige situatie wil veranderen. Show less
Leij, I. van der; Berg, M. van den; Boot, R.G.; Franse, M.; Distel, B.; Tabak, H.F. 1992
Complete sequential H-1 and N-15 resonance assignments for the reduced Cu(I) form of the blue copper protein azurin (M(r) 14 000, 128 residues) from Pseudomonas aeruginosa have been obtained at pH... Show moreComplete sequential H-1 and N-15 resonance assignments for the reduced Cu(I) form of the blue copper protein azurin (M(r) 14 000, 128 residues) from Pseudomonas aeruginosa have been obtained at pH 5.5 and 40-degrees-C by using homo- and heteronuclear two-dimensional (2D) and three-dimensional (3D) nuclear magnetic resonance spectroscopic experiments. Combined analysis of a 3D homonuclear H-1 Hartmann-Hahn nuclear Overhauser (3D H-1 HOHAHA-NOESY) spectrum and a 3D heteronuclear H-1 nuclear Overhauser H-1{N-15} single-quantum coherence (3D H-1{N-15} NOESY-HSQC) spectrum proved especially useful. The latter spectrum was recorded without irradiation of the water signal and provided for differential main chain amide (NH) exchange rates. NMR data were used to determine the secondary structure of azurin in solution. Comparison with the secondary structure of azurin obtained from X-ray analysis shows a virtually complete resemblance; the two beta-sheets and a 3(10)-alpha-3(10) helix are preserved at 40-degrees-C, and most loops contain well-defined turns. Special findings are the unexpectedly slow exchange of the Asn-47 and Phe-114 NH's and the observation of His-46 and His-117 (NH)-H-epsilon2 resonances. The implications of these observations for the assignment of azurin resonance Raman spectra, the rigidity of the blue copper site, and the electron transfer mechanism of azurin are discussed. Show less
Groenen, E.J.J.; Poluektov, O.G.; Matsushita, M.; Schmidt, J.; Waals, J.H. van der; Meijer, G. 1992
Electron-spin-echo experiments at 95 GHz and 1.2 K reveal that the triplet excitation of a single crystal of C60 is delocalized over either a pair or a chain of C60 molecules along <110>... Show moreElectron-spin-echo experiments at 95 GHz and 1.2 K reveal that the triplet excitation of a single crystal of C60 is delocalized over either a pair or a chain of C60 molecules along <110> directions. Two distinct triplet species have been observed in a one-to-one ratio which verifies the proposed 2 a0 face-centred cubic superstructure of the crystal at low temperature. The C60 molecules on the two sublattices differ by a rotation over 60-degrees about <111> directions. Show less
In this paper we show how the use of the Irving–Kirkwood expression for the pressure tensor leads to expressions for the pressure difference, the surface tension of the flat interface, and the... Show moreIn this paper we show how the use of the Irving–Kirkwood expression for the pressure tensor leads to expressions for the pressure difference, the surface tension of the flat interface, and the Tolman length which agree with the expressions found using microscopic sum rules. The use of the Schofield–Henderson expression for the pressure tensor for a particular contour different from the contour that leads to the Irving–Kirkwood expression is found to give incorrect results for the pressure difference and, in particular, also for the Tolman length. The distance between the so‐called mechanical surface of tension and the Gibbs dividing surface is found not to be given by Tolman’s length. Using an approximate expression for the pair density it is possible to find values for the location of the mechanical surface of tension and for Tolman’s length which are in reasonably good agreement with values found by Nijmeijer etal. in molecular dynamics simulations. Show less
