Mössbauer spectroscopic studies of the cores of human, limpet and bacterial ferritins.

Ferritin cores from human spleen, limpet (Patella vulgata) haemolymph and bacterial (Pseudomonas aeruginosa) cells have been investigated using 57Fe Mössbauer spectroscopy. The Mössbauer spectra were recorded over a range of temperatures from 1.3 to 78 K, all the spectra are quadrupole-split doublets with similar quadrupole splittings and isomer shifts, characteristic of iron(III), while at sufficiently low temperatures the spectra of all the samples show well-resolved magnetic splitting. At intermediate temperatures, the spectra from the human ferritin exhibit typical superparamagnetic behaviour, while those from the bacterial ferritin show behaviour corresponding to a transition from a magnetically ordered to a paramagnetic state. The spectra from the limpet ferritin show a complex combination of the two effects. The results are discussed in terms of the magnetic behaviour of small particles. The data are consistent with magnetic ordering temperatures of about 3 and 30 K for the bacterial and limpet ferritin cores, respectively, while the data indicate that the magnetic ordering temperature for the human ferritin cores must be above 50 K. These differences are interpreted as being related to different densities of iron in the cores and to variations in the composition of the cores. The human ferritin cores are observed to have a mean superparamagnetic blocking temperature of about 40 K, while that of the limpet ferritin cores is about 25 K. This difference is interpreted as being due not only to different mean numbers of iron atoms in the two types of core but also to the higher degree of crystallinity in the cores of the human ferritin.

Mössbauer spectroscopic studies of human haemosiderin and ferritin.

Ferritin and haemosiderin isolated from iron-overloaded human spleens have been investigated by 57Fe Mössbauer spectroscopy at temperatures between 1.3 and 200 K and also in applied magnetic fields. Virtually identical spectra were obtained from both materials at the high and low-temperature ends of this range, and also at 4.2 K in an applied magnetic field of 10 T; this indicates that both must contain iron in a closely similar chemical form. The difference between the two materials lies in the temperature dependence of their Mössbauer spectra in the intermediate temperature range, between 10 and 100 K. The temperature dependence of the Mössbauer spectra is characteristic of superparamagnetic behaviour, which occurs when a magnetically ordered material is present in the form of small particles. The details of this temperature dependence are related to the distribution of particle sizes and the magnetic anisotropy constant of each substance. Electron microscopy shows the haemosiderin cores to be markedly smaller on average than those of ferritin. Combining the Mössbauer spectroscopy and electron microscopy data we have shown that the magnetic anistropy constant of haemosiderin is considerably larger than that of ferritin. This is thought to result from the smaller core size and less symmetrical protein shell of the former. These data are consistent with the proposal that haemosiderin is derived from ferritin.

Case management at work for SSA disability beneficiaries: process results of the Project NetWork return-to-work demonstration.

This article presents the results of the process analysis of the evaluation of the Project NetWork demonstration, a Federal demonstration undertaken by the Social Security Administration (SSA) in 1991 to test alternative methods of providing rehabilitation and employment services to SSA's Disability Insurance beneficiaries and Supplemental Security Income disabled and blind applicants and recipients. The major findings are: (1) from an operational standpoint, it is feasible to expand access to vocational rehabilitation (VR) services to a broad spectrum of SSA beneficiaries, and (2) roughly similar results are achieved, in terms of client intake and provision of services, when case management services are provided by SSA staff, contracted out to State VR agencies, or contracted with private VR providers. Later evaluation reports will trace demonstration impacts on earnings and disability benefits and report the overall benefits and costs of return-to-work services for this population.

Design of the Project NetWork return-to-work experiment for persons with disabilities.

As the Nation's first rigorous large-scale evaluation of vocational rehabilitation (VR) assistance to persons with severe disabilities, the Project NetWork demonstration will provide a wide range of information to policy-makers, researchers, and other interest groups. The evaluation of Project NetWork addresses two key policy questions: Is it feasible to increase participation in VR services among Disability Insurance (DI) beneficiaries and Supplemental Security Income (SSI) applicants/recipients through a combination of intensive outreach, case management, and enhanced work incentives? Do the interventions tested produce net benefits from the perspective of participants, society, the DI Trust Fund, and the Federal Government, as a whole? The study utilizes a randomized field experiment design to evaluate the net impact of the demonstration on participant employment, earnings, receipt of transfer benefits, social and psychological well-being, and other variables of interest to policymakers. A combination of SSA administrative data, information from the demonstration's onsite management information system (MIS), and in-person interviews (containing a rich array of information on disability, health, and attitudes) supports the evaluation. This article summarizes three aspects of the evaluation: Its experimental and sample design; the methods and data to be used to analyze project benefits, costs, and participation; and the challenges faced during demonstration implementation. It also presents preliminary data on the characteristics of Project NetWork participants and eligibles.

A method for the cryopreservation of red blood cells using hydroxyethyl starch as a cryoprotectant.

A simple, quick, inexpensive and long term method of cryopreserving human red cells using hydroxyethyl starch (HES) as a cryoprotectant is described. No sophisticated equipment or skilled labour is required. As HES is a plasma expander, it does not have to be removed prior to transfusion, thereby obviating the requirement for a washing stage. This allows 60 units/h to be prepared. As the microbiological integrity of the system is maintained, there is potential for prolonged storage post-thaw at 4 degrees C. Recoveries of 99% and 30 min saline stabilities in excess of 91% have been consistently achieved. P50O2 and 2,3DPG values are not significantly decreased.

Spectroscopic studies of the nature of the iron clusters in the soluble hydrogenase from Desulfovibrio desulfuricans (strain Norway 4).

57Fe-enriched samples of the soluble hydrogenase from Desulfovibrio desulfuricans (Norway) have been investigated in both the native (oxidized) and the dithionite-reduced states using Mössbauer spectroscopy. The data clearly show that the iron in this enzyme is predominantly in the form of iron-sulphur clusters which are closely similar to the [4Fe-4S] clusters found in a large number of ferredoxins, such as that from Bacillus stearothermophilus. There appear to be two [4Fe-4S] clusters. The iron-sulphur clusters in the oxidized protein are virtually diamagnetic, as indicated by Mössbauer, electron spin resonance and magnetic circular dichroic spectroscopy. On reduction by dithionite + methyl viologen, Mössbauer spectroscopy showed that only 50% of the [4Fe-4S] clusters were reduced. Even reduction with hydrogen up to a pressure of 23 GPa did not reduce the iron-sulphur clusters completely. An ESR signal due to a rapidly relaxing species with g = 2.03, 1.89 was observed in the reduced protein, together with a weaker spectrum from a slower-relaxing species at g = 2.34, 2.12.