O2-sensitive

In A. vinelandii, C-terminal cleavage occurs in crude extracts after restoration of nickel and requires hours rather than minutes, as is the case in vivo. It does not require de novo protein synthesis and surprisingly is not redox or O2 sensitive. Also, it is not inhibited by well-established inhibitors of metallo- or serine protease families (Menon and Robson 1994). 

The work on biomimetic models for [NiFe] and [FeFe] hydrogenase has been described in several review articles [15b 158]. In this work, many of the structural features important for proper function found in the native systems have been successfully incorporated for example, the bimetallic Ni-Fe or Fe-Fe core with rather short metal-metal distances and an open coordination site at one metal, the sulfur-rich environment (terminal and bridging thiolate ligands), CO/CN ligation of the iron(s), and the incorporation of a base for acceptance of the proton and, more recently, of hydride bridges. Still-existing problems of many model systems are the O2 sensitivity, the high overpotentials, and lack of activity (low turnover rates). 

Nitrogenases are also extremely labile in an O2 environment. Cyanobacteria have adopted two strategies to overcome the O2 sensitivity of the nitrogenase reaction, either temporal or spatial separation of O2 evolution and H2 production. Temporal separation has been achieved mainly in non-heterocystous unicellular cyanobacteria such as Gloeothece sp. strain ATCC 27152 and Plectonema boryanum. Nitrogen fixation occurs only in darkness, during which respiration of the carbohydrates, syn... 

Cysteine ligands have also been reported in the synthesis of intricate copper nanoparticles following a literature modified reduction procedure. The Cu° nanoclusters revealed a plasmon resonance band at 398 nm and an average size distribution of 3.5 0.8nm by TEM. Infrared analysis of the stabilized nanoparticles showed a weakened S-H stretch at 2598 cm suggesting uncoordinated cysteine thiols, supporting the possible involvement of the amine functional group from the cysteine alpha carbon in particle stabilization. These particles displayed extreme O2 sensitivity, degrading under aerobic conditions to Cu (I) and then Cu (II) cysteine complexes. Additionally, this sensitivity precluded the convenient determination of nanoparticle crystallinity. ... 

Since conventional nitrogenase is uniformly very O2 sensitive across the spectrum of physiological types (Gallon, 1992), physical mixing in planktonic systems has been recognized as a potentially important factor in regulating N2 fixation, particularly for... 

Secondary arsines are usually oxidized to yield the corresponding diarsines (equation 9) they themselves are often extremely O2 sensitive and can easily be converted to give arsinous acid anhydrides (diarsoxanes) (equation 10) and finally (see above) arsinic acid (equation 11). 

Singlet oxygen O2 Sensitized by light-absorbing dissolved organic matter (humic acids)... 

Archer SL, Weir EK, Reeve HE, MichelaJds E. 2000, Molecular identification of O2 sensors and O2-sensitive potassium channels in the pulmonary circulation. Adv Exp Med Biol 475 219-240,... 

Membrane-covered optochemical sensors (optodes) with O2 sensitive or pH sensitive fluorescence indicators (e.g. pyrene butyric acid or hydroxypyrene trisulfonic acid) have been coupled with different enzyme reactions, such as the conversion of glucose, lactate, ethanol, or xanthine, and with antigen-antibody couples (Opitz and Lubbers, 1987). 

Oscillatory reactions provide one of the most active areas of research in contemporary chemical kinetics and two published studies on the photochemistry of Belousov-Zhabotinsky reaction are very significant in this respect. One deals with Ru(bpy)3 photocatalysed formation of spatial patterns and the other is an analysis of a modified complete Oregonator (model scheme) system which accounts for the O2 sensitivity and photosensitivity. ... 

A Pliotochemically generated O2 sensitizer 1. rubrene 2. methylene blue. 

Studies on Fe-S clusters are generally hindered by the lack of distinctive optical-absorption features and by low reduction potentials and O2 sensitivity. Techniques established for their characterization do not, furthermore, allow the investigator to view and monitor rapid changes in cluster structure as they may occur or be induced during an experiment. Consequently, in what may turn out to be a large number of cases, the rich chemistry that stems from the framework of Scheme 4 has been difficult to define or control. As discussed now and in Sect. 5, voltammetric methods are providing new possibilities and insight. 

Postnatal Maturation of the Carotid Chemoreceptor O2 Sensitivity at the Cellular Level... 

---