High Protection Factor Research Articles

The pH dependence of hydrogen-deuterium exchange in trp repressor: the exchange rate of amide protons in proteins reflects tertiary interactions, not only secondary structure.

The pH dependence of amide proton exchange rates have been measured for trp-repressor. One class of protons exchanges too fast to be measured in these experiments. Among the protons that have measurable hydrogen-deuterium exchange rates, two additional classes may be distinguished. The second class of protons are in elements of secondary structure that are mostly on the surface of the protein, and exchange linearly with increasing base concentration (log kex versus pH). The third class of amide protons is characterized by much higher protection against exchange at higher pH. These protons are located in the core of the protein, in helices B and C. The exchange rate in the core region does not increase linearly with pH, but rather goes through a minimum around pH 6. The mechanism of exchange for the slowly exchanging core protons is interpreted in terms of the two-process model of Hilton and Woodward (1979, Biochemistry 18:5834-5841), i.e., exchange through both a local mechanism that does not require unfolding of the protein, and a mechanism involving global unfolding of the protein. The increase in exchange rates at low pH is attributed to a partial unfolding of the repressor. It is concluded that the formation of secondary structure alone is insufficient to account for the high protection factors seen in the core of native proteins at higher pH, and that tertiary interactions are essential to stabilize the structure.

Stability of alpha-helices in a molten globule state of cytochrome c by hydrogen-deuterium exchange and two-dimensional NMR spectroscopy.

To distinguish between intrinsically stable helices and those stabilized by the protein three-dimensional structure, we report the hydrogen-deuterium exchange (H2H) rates of 29 amide protons of ferricytochrome c in a molten globule state (at 35 degrees C, pH 2.0 with 0.5 M KCl), monitored by 2D-NMR. The results of the H2H-exchange experiments have been analyzed to calculate the protection factors. The helices were not uniformly stable and amide protons of residues belonging to the N and C-terminal helices had high protection factors. The protection factors of amide protons involved in the 50's helix were low, and could not be determined quantitatively. In the 60's helix we found two amide protons with protection factors comparable to those of the N and C-terminal helices. These results, compared with previously reported intrinsic helicities of peptide fragments, indicate that the relative helicities of isolated fragments are not directly reflected in the stability of the helices in the molten globule state, even though this state has no rigid tertiary structure. This suggests that loose interactions between helices are present in the molten globule state of cytochrome c, and that they are essential for keeping the helicity of the helical segments. The loose tertiary interactions discussed here differ from the usual tertiary interaction found in the native state in that the specific interdigitization between side-chains is absent.

Stability of α-helices in a molten globule state of cytochrome c by hydrogen-deuterium exchange and two-dimensional NMR spectroscopy

To distinguish between intrinsically stable helices and those stabilized by the protein three-dimensional structure, we report the hydrogen-deuterium exchange (H2H) rates of 29 amide protons of ferricytochrome c in a molten globule state (at 35°C, pH 2.0 with 0.5 M KCl), monitored by 2D-NMR. The results of the H2H-exchange experiments have been analyzed to calculate the protection factors. The helices were not uniformly stable and amide protons of residues belonging to the N and C-terminal helices had high protection factors. The protection factors of amide protons involved in the 50's helix were low, and could not be determined quantitatively. In the 60's helix we found two amide protons with protection factors comparable to those of the N and C-terminal helices. These results, compared with previously reported intrinsic helicities of peptide fragments, indicate that the relative helicities of isolated fragments are not directly reflected in the stability of the helices in the molten globule state, even though this state has no rigid tertiary structure. This suggests that loose interactions between helices are present in the molten globule state of cytochrome c, and that they are essential for keeping the helicity of the helical segments. The loose tertiary interactions discussed here differ from the usual tertiary interaction found in the native state in that the specific interdigitization between side-chains is absent.

実作業場におけるマンテスト法による全面マスクの防護性能評価

From a practical angle of view to estimate the protection factors (PFs) provided by full-face masks, a number of protection factors were measured with a man-test apparatus just before the wearers started to do radiation work in radiation controlled area. PFs of the total number of 2, 279 cases were measured under five simulated working conditions. The measured PFs were widely distributed from 2.3 to 6, 700. About 95% of workers obtained PFs more than 50, and about 64% showed much higher PFs more than 1, 000 due to good fitting. In the case of some persons, the measured PFs irregularly varied and changed to a large degree. This method is a reliable technique that has been confirmed to protect unexpected internal exposure. From the results obtained, the method should be necessary to provide a better mask and higher PF for each worker.

Composite Materials for X-ray Protection

We have developed and tested a radiation protection material that provides similar attenuation for diagnostic x-ray spectra to that of conventional Pb apron materials with approximately 30% reduced weight. By combining a number of elements with different K absorption energies, such as Ba, W, and Pb, energy attenuation for given spectra can be optimized with respect to total cross-sectional mass loading. Alternatively, garments with much higher protective factors at equivalent weight to conventional garments could be produced. The reduction in the amount of Pb used also reduces problems associated with the toxicity of the material during manufacture and disposal. Back strain can be reduced for personnel performing special radiological procedures that require wearing protective garments for long periods of time.

Sunscreens and phototesting

The last decade has seen numerous advances in the development of photoprotective sunscreens. There have been significant improvements in the sunscreening chemicals as well as vehicle preparations, yielding much higher protection factors and enhanced substantivity. In addition, novel sunscreening chemicals are currently being explored that provide protection against ultraviolet A (UVA) radiation. This chapter briefly describes both traditional and novel methods for evaluating sunscreening agents, discusses the recent evidence supportive of the view that UVA and infrared radiation exert pathologic changes in the skin, and provides the private dermatologist with additional information by which he or she can better understand the sunscreen literature and manufacturers' claims.

Hydroa vacciniforme—a review of ten cases

Ten patients, eight female and two male, with Bazin's hydroa vacciniforme (HV) are reviewed. Onset occurred between the ages of 1 and 11 years and has persisted indefinitely in all but three cases where the disease gradually improved during adolescence. Recurrent episodes of itching occurred on light-exposed areas within hours of sun exposure, leading to scattered erythematous papules followed by small tense vesicles. Gradual healing left pock-like scars. Cutaneous phototesting by monochromator revealed reduced minimal erythema doses at 340 nm in three patients and also at 360 nm in one of these. Histology showed focal intraepidermal spongiotic vesiculation leading to epidermal and upper dermal necrosis with a chronic inflammatory cell infiltrate. One patient showed features of leukocytoclastic vasculitis. Direct immunofluorescence in one patient showed granular C3 and fibrin deposits below the basement membrane zone. Viral studies, assessment of DNA repair, antinuclear factor titre, urinary amino acid screen, porphyrin screen and routine haematology and biochemistry were all normal. High protection factor UV-A-filtering sunscreens in six patients, low dose UV-B therapy in two patients and antimalarials in two patients were moderately helpful. β-Carotene, thalidomide and low dose PUVA were ineffective. HV is therefore a distinct clinical and histological entity associated with demonstrable UV-A sensitivity approximately: in 30% of patients. Sunscreens are the most effective therapeutic agents, but low-dose UVTB or antimalarial therapy may also be tried.