Alkema, D., see P. A. Hader 136 (1981) 65 arachidonic acid by rabbit neutrophils 136 (1981) 293 Amons, R., see A. T. Gudkov 136 (1981) 235 Bowers, W. E., see E. H. Harrison 136 (1981) 289 Anzai, H., see F. Kawamura 136 (1981) 244 Braznlkov, E. V., see D. A. Dolgikh 136 (1981) 311 Appelt, K., see M. Kimura 136 (1981) 58 Brethes, D., see C. Garret 136 (1981) 216 Arad, G. and T. J. C. Beebee, Measurement Burdge, E. L. and K. G. Wilson, Regulation of 5 S RNA accumulation in oocytes of of the aspartate pathway in isolated Xenopus laevis using a cDNA probe 136 (1981) 247 pea chloroplasts: Effects of S-2-aminoArseniev, A. S., Yu. N. Utkin, V. S. Pashkov, ethylcysteine and threonine on the V. I. Tsetlin, V. T. Ivanov, V. F. Bystrov metabolism of labeled aspartate and Yu. A. Ovchinnikov, 19F NMR deter136 (1981) 322 Burmeister, M., see P. Graber 136 (1981) 25 mination of intramolecular distances in Bystrov, V. F., see A. S. Arseniev 136 (1981) 269 spinand fluorine-labelled proteins: Bychkova, V. E., see D. A. Dolgikh 136 (1981) 311 Neutrotoxin II Naja naja ox&a 136 (1981) 269 Avigliano, L., J. L. Davis, M. T. Graziani, Carrillo, N., see R. Wagner 136 (1981) 208 A. Marchesini, W. B. Mims, B. Mondovi Charriaut, C., see M. Bare1 136 (1981) 111 and J. Peisach, Electron spin echo specChevallier, J., see C. Garret 136 (1981) 216 troscopy studies of type 1 and type 2 Christen, P., see H. Wacker 136 (1982) 329 copper in Rhus vernicifera lactase and Ciudad, C. J., see M. A. Mor 136 (1981) 131 in Cucurbita pepo medullosa ascorbate Claesson, H.-E., see S. J. Feinmark 136 (1981) 141 oxidase 136 (1981) 80 Clore, G. M., see A. M. Gronenborn 136 (1981) 160 Cohen, P., see A. Morel 136 (1981) 316 Bandman, E., R. Matsuda, J. MicouCook, G. M. W., see N. G. Rutherford 136 (1981) 105 Eastwood and R. Strohman, In vitro translation of RNA from embryonic and Contencas, P., see C. Rodrigues-Pousada 136 (1981) 239 Costa, J. L., C. M. Dobson, D. D. Fay, K. L. from adult chicken pectoralis muscle Kirk, F. M. Poulsen, C. R. Valeri and produces different myosin heavy chains 136 (1981) 301 J. J. Vecchione, Nuclear magnetic resoBarel, M., C. Charriaut and R. Frade, Isolanance studies of amine storage in pig tion and characterization of a C3b recepplatelets 136 (1981) 325 tor-like molecule from membranes of a Cottin, P., P. L. Vidalenc and A. Ducastaing, human B lymphoblastoid cell line (raji) 136 (1981) 111 Ca*+-Dependent association between a Baudras, A., see A. M. Gronenborn 136 (1981) 160 Ca”-activated neutral protelnase Baumann, C. M. and H. Riidiger, Interac(CaANP) and its specific inhibitor 136 (1981) 221 tions between the two lectins from Vi& Cousineau, C., see J. Sinclair 136 (1981) 213 cracca 136 (1981) 279 Cox, R. A. and J. M. Kelly, A study of the Becker, E. L., see B. J. Bormann 136 (1981) 293 arrangement of 18 S rRNA within 40 S Beebee, T. J. C., see G. Arad 136 (1981) 247 subparticles of rabbit ribosomes 136 (1981) 306 Bell, R. A., see D. Alkema 136 (1981) 70 Bennoun, P., Does the chloroplast control D’Alagni, M. de Petris and G. B. Marinimitochondrial functions? 136 (1981) I Bettolo, On the interaction between Ben-Zeev, O., H. Schwalb and M. C. Schotz, Jatrophone and DNA 136 (1981) 175 Interaction of two fractions of heart Dautrevaux, M., see S. Djoumessi 136 (1981) 145 lipoprotein lipase with natural and synDavis, J. L., see L. Avigliano 136 (1981) 80 thetic substrates 136 (1981) 95 Djoumessi, S., J. Rousseaux and M. Blbkberg, L., D. Lombardo, 0. Hernell, Dautrevaux, Structual studies of a new 0. Guy and T. Olivecrona, Bile salthemoglobin: HbJ Lens, p13(AIO) stimulated lipase in human milk and Ala -+ Asp 136 (1981) 145 carboxyl ester hydrolase in pancreatic De Boer, P. A. J., see A. F. M. Moorman 136 (1981) 45 juice: Are they identical enzymes? 136 (1981) 284 De Laaf, R. T. M., see A. F. M. Moorman 136 (1981) 45

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Mg-ATP binds to the iron protein component of nitrogenase. The magnetic field dependence of the linear electric field effect (LEFE) in pulsed EPR is consistent with a single 4Fe-4S cluster. The LEFE is virtually unaltered when Mg-ATP is bound. Electron spin echo envelope modulation techniques were employed to evaluate the possibility of a magnetic interaction between 31P of Mg-ATP and the Fe-S center of the iron protein. None was detected. However, weak modulations possibly attributable to peptide 14N were seen, and these were slightly shifted by Mg-ATP addition. Further, protons in the vicinity of the Fe-S cluster of the protein readily exchange with D2O, and this process is unaffected by Mg-ATP.

Three-pulse electron-spin-echo envelopes have been measured for frozen solution samples of horse heart ferric cytochrome c both before and after exchange against D20. The deuterium modulation pattern was enhanced relative to modulation patterns due to coupled 14N nuclei by dividing the envelope obtained with the nondeuterated sample into the envelope obtained with the deuterated sample. Measurements of the modulation depth were made by fitting single cycles of a decaying waveform having the free deuterium NMR period to early portions of the experimental quotient waveform. The observed modulation depth was compared with the depth calculated theoretically from X-ray crystallographic data. The good agreement obtained in this comparison demonstrates the reliability of the electron-spin-echo method as a means of studying the distance and/or distribution of exchangeable hydrogen nuclei in the vicinity of sufficiently well-characterized protein metal-ion active sites.

Rieske-type iron/sulfur proteins and several NADH-dependent oxygenases contain Fe/S clusters with similar spectral and magnetic properties. Purified Rieske iron/sulfur protein from Thermus thermophilus contains two apparently identical [2Fe-2S] clusters in a polypeptide having only four cysteine residues, and it has been proposed that each Fe/S cluster is coordinated to two cysteine S-atoms and to an unknown number of other non-sulfur atoms (Fee, J. A., Findling, K. L., Yoshida, T., Hille, R., Tarr, G. E., Hearshen, D. O., Dunham, W. R., Day, E. P., Kent, T. A., and Munck, E. (1984) J. Biol. Chem. 259, 124-133). We have examined the Rieske protein from Thermus and the phthalate dioxygenase from Pseudomonas cepacia with electron nuclear double resonance (ENDOR) and pulsed EPR methods and report here evidence for the direct coordination of nitrogenous ligands to the Fe/S clusters in these proteins. The electron nuclear double resonance signals arising from 14N have been interpreted in terms of a strongly coupled ligand with AN = approximately 26-28 MHz and a weakly coupled ligand with AN = approximately 9 MHz. The pulsed EPR spectrum shows a rich pattern of lines in the Fourier transformed data having peaks in the range of 0.8 to 6.7 MHz. The lower frequency resonances are tentatively associated with coupling of the unpaired spin to the remote N-atoms of coordinated imidazole rings.

Using electron spin echo envelope spectroscopy, we have proven that the water close to heme in metmyoglobin is bound to the iron. For protein samples exchanged against D2O, we show that the electron nuclear coupling for 2H is 0.8 MHz. This coupling is considerably smaller in methemoglobin, pointing out a fundamental difference in bonding to water.

From a study of the magnetic field dependence of the linear electric field effect (LEFE) in EPR spectroscopy, we demonstrate that iron-sulfur cluster 3 in air-oxidized, beef heart succinate-ubiquinone oxidoreductase (Complex II) is a 3-iron cluster. This suggests that cluster 3 may arise by oxidative degradation from a 4-iron cluster originally present in the enzyme and may be reconverted back into a 4-iron cluster under reducing conditions. Linear electric field effect studies of succinate-reduced Complex II are in accord with the view that cluster 1 is a 2-iron cluster.

The characteristic deuterium modulation pattern was observed in the electron spin-echo envelopes for laccase, decupro laccase (from which Type 2 copper had been removed), stellacyanin, and azurin that had been exchanged against D2O. From the decay rate of the modulation pattern and from a quantitative analysis of the modulation depth, we conclude that the Cu(II) sites in these proteins are directly accessible to solvent. Similar results were obtained for laccase and decupro laccase.

The electron spin-echo decay envelope is commonly observed to be modulated by frequencies characteristic of nuclei situated near the electron spin. Fourier transformation of this envelope can therefore be made to yield a spectrum similar to the ENDOR spectrum. The echo envelope method possesses some advantages over the ENDOR method, in particular when the electron-nuclear coupling is weak, or when the sample can only be prepared in frozen solution or powder form. However, it is beset by the problem of an instrumental dead time, which prevents observation of the initial portion of the envelope. A technique for estimating the form of this initial portion and thus minimizing the spectral artifacts associated with the dead time is described here. It is illustrated with both simulated and experimental echo envelope data.

We have examined the structure of Cu(II)-(histidine)2 in solution using optical, electron paramagnetic resonance (EPR) and electron spin-echo (ESE) spectroscopies. Histidine is a potential tridentate ligand with three groups capable of binding Cu(II): 1) carboxyl oxygen 2) imidazole nitrogen and 3) amino nitrogen. Histidine is involved in the coordination of metal ions in a number of copper proteins, including superoxide dismutase, ceruloplasmin, ascorbate oxidase, galactose oxidase, etc. In addition, histidine has been implicated in the in vivo transport of copper between albumin and cells.

For both the [2Fe-2S] and the [4Fe-4S] ferredoxins, dialysis against 2H2O prior to single electron reduction leads to the appearance of a deuterium modulation pattern in the electron spin echo decay envelope indicative of deuteron-proton exchange very near the paramagnetic center. In contrast, if the ferredoxin is exposed to 2H2O after its reduction in H2O, far less deuterium exchange near the metal center takes place. Thus, proton exchange with solvent is in part dependent on the redox state of the protein. For high potential iron-sulfur proteins, this type of proton-deuteron exchange near the metal center does not occur unless the protein is partially unfolded in dimethylsulfoxide in 2H2O.

Titrations of the paramagnetic rate earth ions Ce(III), Nd(III), Er(III), and Yb(III) with ATP, ADP, adenosine, and the hexametaphosphate ligands have been performed in order to establish the conditions required to form saturated complexes. These titrations have been made by recording the decay envelope of electron spin echoes for a range of different concentrations of the species concerned and observing the ‘nuclear modulation effect’ in the echo envelope. This novel method can be used when optical titrations are not feasible. It also yields additional information concerning changes in the number and nature of the coordinating groups, in the distances of these groups from the paramagnetic ion, and in the degree of water coordination in the primary sphere. It was shown that: (a) ATP has a greater affinity than ADP for rate earth ions; (b) Ce(III) has a greater affinity than Nd(III) for ATP; (c) the interaction between rate earth ions and 31P nuclei in the added phosphates is greatest for cations with the smallest radii; (d) more phosphate groups are bound in hexametaphosphate complexes of rate earth ions than in the corresponding ATP complexes; (e) some of the coordination sites in rare earth ATP complexes are occupied by water. In othe studies performed with paramagnetic transition metal ions, it was shown that Co(II) can, under certain conditions, bind to the adenine moiety of ATP.

We describe a method for the differentiation of 3iron from 2-iron and 4-iron Fe/S proteins based on consideration of both the magnetic field dependence of shifts in g induced by an externally applied electric field (LEFE) and the continuous wave EPR spectra properties.The magnetic field dependence and the magnitude of the LEFE for 3-iron ferredoxins are similar to those for 4-iron ferredoxins but differ considerably from those for 2-iron ferredoxins or for high potential iron proteins.Furthermore, as 3-iron ferredoxins and high potential iron proteins are EPR-active when oxidized while 2-iron and 4-iron ferredoxins are only EPR-active when reduced, the differentiation among all of them can be made on the basis of both continuous wave EPR and LEFE properties, but not by each individually.

Electron spin echo envelope spectroscopy was used to probe the two metal binding sites of Cu(II)-conalbumin. The echo envelope spectrum of Cu(II)-conalbumin-oxalate, with metal ion at either one or both of the binding sites, contains lines arising from the interaction of the electron spin of Cu(II) with bound imidazole, demonstrating histidine ligation to the metal ion. The 13C superhyperfine interaction of bound [13C]oxalate, obtained from the ratio of the electron spin echo envelopes of Cu(II)-conalbumin-[13C]oxalate to that of Cu(II)-conalbumin-[12C]oxalate, is about twice the free precession frequency and indicates a contact interaction between 13C and Cu(II). This study indicates that oxalate is directly coordinated to the metal ion. Over the pH range 7.0 to 10.0, where Cu(II)-conalbumin binds carbonate as an associated anion, the echo envelope spectrum indicates that at least one imidazole ligand is coordinated to Cu(II). Below pH 6.0 and above pH 11.0, imidazole coordination is not observed.

Optical, electron paramagnetic resonance, and electron spin-echo envelope spectroscopies were used to examine the structure of the Cu(II) complex of glycyl-L-histidyl-L-lysine (GHL) in solution. At neutral pH, GHL forms a mononuclear 1:1 Cu(II) compound having an EPR spectrum resembling that of Cu(II) equatorially coordinated by two or three nitrogen atoms. Electron spin-echo studies demonstrate that one of these is located in the histidyl imidazole ring. A pH titration of Cu(II)-GHL shows three optical transitions with apparent pKs of 3.6, 9.2 and 11.4 and molecularities, with respect to protons, of 2, 2, and 1, respectively. At the lowest pK, GHL binds Cu(II), forming the species present at physiological pH. At elevated pH, spectroscopic experiments suggest that an alteration of the Cu(II) structure occurs, yet the bound imidazole is retained. These solution studies are consistent with nitrogen coordination of Cu(II) in Cu(II)-GHL, but the solid-state polymeric structure, with oxygen-bridged Cu(II) pairs as previously determined by X-ray crystallographic analysis [Pickart, L., Freedman, J. H., Loker, W. J., Peisach, J., Perkins, C. M., Steinkamp, R. E., & Weinstein, B. (1980) Nature (London) 288, 715-717; C. M. Perkins, N. J. Rose, R. E. Steinkamp, L. H. Jensen, B. Weinstein, and L. Pickart, unpublished results], does not exist in solution.

AbstractElectron spin echo studies have been performed on the model compound for cytochrome a, bis imidazole heme a, and the results compared with those obtained for bis imidazole protoheme and for cytochrome a. The 14N coupling with the iron in the heme a model compound, as obtained from a study of the nuclear modulation effect, is comparable with that seen for the bis imidazole complex of protoheme. The magnetic field dependence of the linear electric field effect is essentially the same in both bis imidazole complexes, but is markedly different from that observed for cytochrome a.15 Thus the odd field component of the crystal field in bis imid heme a is different from that in cytochrome a.

Echo envelope spectrometry, a method for obtaining the electron–nuclear superhyperfine spectrum by transforming the electron spin echo decay envelope into the frequency domain, is limited in its effectiveness by the presence of an appreciable dead time following the microwave transmitter pulses. We describe here a simple passive addition to the microwave circuit which can reduce the dead time by 1.5:1. The performance of an electron spin echo spectrometer with and without this accessory is compared.

We have studied the Cu(II), Co(II), and Fe(III) complexes of the antineoplastic drug bleomycin by using electron spin--echo envelope spectroscopy. For all three complexes, nitrogen coordination of the metal ions is demonstrated. For the Cu(II)-- and Co(II)--drug complexes, we have been able to identify imidazole as a metal ligand.

We have measured the linear electric field effect for peroxide-activated yeast cytochrome c peroxidase and for the mercaptoethanol derivative of Neurospora tyrosinase. Although both of these materials have EPR spectra resembling those of free radicals, the linear electric field effect measurements demonstrate that there is a metal ion associated with the paramagnetic centers. In addition, we have also observed superhyperfine interactions with 14N nuclei.