2ϩ cluster in the presence of O 2 remains to be elucidated (10). Nevertheless, the decrease in site-specific DNA binding and in the extent of dimerization that occurs concomitant with cluster conversion provides a reasonable explanation for why FNR is only active as a transcription factor under anaerobic conditions in vitro (11,13,14). Furthermore, 2ϩ to 2ϩ cluster conversion in FNR has also been observed in vivo following exposure of anaerobically maintained cells to air (15). Thus, inactivation of FNR by O 2 appears to be mediated by an O 2 -sensitive [4Fe-4S] 2ϩ cluster both in vitro and in vivo. Although these investigations have provided clear insights into how FNR from anaerobic cells is inactivated by O 2 , much less is known about how FNR is maintained in an inactive state under aerobic growth conditions. Although WT-FNR purified from aerobically grown cells has previously been shown to lack any Fe-S cluster 17)), it is not known if this apo-FNR arises from the continuous destruction of [4Fe-4S] cluster assembly under these growth conditions. Techniques to distinguish between these two possibilities for WT-FNR are not * This work was supported in part by National Institute of Health Grants GM-45844 (to P. J. K.) and GM-22701 (to E. M.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.† Deceased.
Background: The nasal valve area is the narrowest region of the entire upper airway. Numerous procedures and spreader devices are published to widen the nasal valve or to stabilize it, but the indications are based only on the surgeon's experience. Methods: In 30 healthy volunteers the deflection of elastic steel elements touching the lower nasal side at its deepest point was precisely measured by means of strain gauges. The deflection was calibrated by standard calibration devices. A special 4-phaserhinomanometer (4RHINO/ Rhinolab/Germany) with a protective face mask allowed simultaneous measurements of the airflow and differential pressure. All signals were recorded simultaneously on both sides. The measurements have been carried out as unilateral measurements according to anterior rhinomanometry. Results: Surprisingly the lateral nasal wall is already moving during quiet breathing. The airflow and its acceleration as well as the pressure difference generating a complete closure of the nose can be determined and has expectedly a high variance between individuals. Conclusions: The elastography confirms the loops in 4-phase-rhinomanometry as symptomatic for the nasal valve elongation and will after developing as medical product allow the systematic quantitative measurement of the influence of the nasal valve on the nasal air stream.
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