S. G. Cohen

Mössbauer spectroscopy of Escherichia coli and its iron-storage protein

57Fe Mössbauer spectra of whole frozen Escherichia coli cells and of an iron storage protein isolated from iron-rich cells of E. coli have been measured over a range of temperatures down to 0.08 K. The spectra of E. coli cells with high iron content and of the iron storage protein were found to be very similar. Above 4 K these spectra consist of a quadrupole split doublet characteristic of Fe3+. Below 3.5 K, the spectra display magnetic hyperfine splitting which is temperature dependent, and point to the existence of an ordered magnetic phase associated with a saturation magnetic hyperfine field of 43 tesla in both samples. The results indicate that the bulk of iron in the iron-rich cells is in the form of aggregates similar in nature to the iron cores in the isolated protein, although the latter account for not more than 1% of the total iron in the cells. The Mössbauer spectra of the isolated protein are different from those observed in ferritin, the iron-storage protein of plants and higher animals, showing that the iron cores in these two proteins are different.

Study of storage iron in cultured chick embryo fibroblasts and rat glioma cells, using Mössbauer spectroscopy

57Fe Mössbauer spectra of normal and Rous sarcoma virus-infected cultured chick embryo fibroblasts and rat glioma cells have been measured between 0.08 and 318 K. Ferritin-like iron and bacterio-ferritin-like iron have been found in these cells, in various relative amounts, indicating a close relationship between the two storage materials. The bacterio-ferritin-like iron was found to be predominantly membrane-bound. Above 260 K very wide lines were observed in the Mössbauer spectra, yielding an effective viscosity of about 1 poise in the normal chick embryo fibroblasts and about 0.5 poise in the virus-infected chick embryo fibroblasts.

Bound-state beta-decay and kinematic search for neutrino mass

A new method involving Doppler spectroscopy with laser techniques is proposed to observe bound-state β-decay of tritium. This process, although theoretically expected to occur, has not yet been observed. The proposed method is, in principle, capable of exposing a finite mass of the neutrino. The low source temperatures and laser spectroscopic resolution necessary for a neutrino mass measurement, although extremely difficult to achieve, appear accessible with conceivable advances of these techniques.

Ferredoxin from Halobacterium of the Dead Sea--Mössbauer and EPR spectra and comparison with Mössbauer spectrum of whole cells.

Recoil-free measurements were carried out on a 2 Fe-ferredoxin, which was isolated and purified from an extreme halophile, Halobacterium of the Dead Sea. The spectrum of this ferredoxin in the oxidized state at 82 K is a superposition of two quadrupole doublets, representing two non-equivalent Fe3+ sites of equal intensity. The spectrum of the reduced ferredoxin is consistent with the presence of two pure classes of iron atoms, ferric (lower isomer shift) and ferrous (higher isomer shift). Interpretations of the recoil-free spectra are discussed. Mössbauer measurements were also carried out on frozen whole bacterial cells and the resulting spectrum was found to be quite different from that observed in the isolated ferredoxin. Tentative conclusions are reached concerning the localization of this ferredoxin in the cytosol of the Halobacteria.The EPR spectrum of the reduced ferredoxin obtained at 24 K exhibits rhombic symmetry with the following g values: 1.894, 1.984 and 2.07. These values are similar to those obtained with 2 Fe-ferredoxins of the plant type, except that the gy and gz values are somewhat higher. Both from the EPR and Mössbauer data, it is deduced that the spin relaxation times in reduced halophilic ferredoxins are faster than in the reduced plant ferredoxins.

Evidence for temperature dependent anisotropic diffusive motion of heme iron in crystals of myoglobin through Mossbauer spectroscopy

A careful investigation of Mössbauer absorption of57Fe in an assembly of unaligned crystals of deoxymyoglobin has revealed asynimetric shapes of the spectra in the range of temperatures between −25C and 25C, which includes the physiological significant temperatures. The asymmetry increases with temperature. The spectral shapes, displaying wide wings, show the presence of modes of collective diffusive motion in which the Fe atoms participate. The results are interpreted in terms of temperature-dependent anisotropic dynamics of the slow collective diffusive modes, based on a model of bounded diffusion assuming absorption in an anisotropic harmonic oscillator in Brownian motion. For example, assuming eqQ > 0, and axial symmetry, we obtain at 20C,=0.040Å2 and = 0.016Å2.