Native system

Serotoninergic System. Figure 1 Graphical representation of the current classification of 5-hydroxytryptamine (5-HT) receptors. Receptor subtypes represented by shaded boxes and lowercase designate receptors that have not been demonstrated to definitively function in native systems. Abbreviations 3-5r cyclic adenosine monophosphate (cAMP) phospholipase C (PLC) negative (-ve) positive (+ve)... 

Long-term aim of our project is the construction of a biomolecular device for hydrogen production in combination with light-driven water-splitting as it occurs in the natural process of photosynthesis in plants. Such a semiartificial device should combine the best suited components found in various native systems which - up to now - cannot be found in an individual native system due to incompatibilities and/or different origin (pro- and eukaryotic, meso- and thermophilic, aerobic - anaerobic environment). Advantage of such a system is... 

Cytochrome P-450 has been characterized in four stable states [Fe, Fe " RH, Fe RH, (O2—Fe ) RH (metastable)] during its oxygenase reaction cycle. In the complete native system a flavoprotein and a redoxin (putidaredoxin) act as electron donors but also as effectors that complement the cytochrome. In the more complex microsomal system the sequence and intermediates are less well defined the electron-transfer chain contains two flavoproteins and one cytochrome, whose interactions with cytochrome P-450 are still the subject of great controversy. 

Due to this early work it became clear that the application of EPR techniques to the OEC would deliver very valuable information on the electronic and geometrical structure of this important enzyme. The work led to an enormous amount of publications in this field both on the native system and on related model compounds. These cannot all be discussed here in detail. In particular, the diverse field of synthetic Mn complexes serving as models for the OEC will not be reviewed the reader is referred to some review articles41 432 438 and a monograph edited by Pecoraro.439... 

Biophysical investigations of mutant Cavl.l channels in a variety of heterologous and native systems have also given varying results, some contradictory (Table 4). Although contested, a dominant theme appears to be a reduced current density and reduced rate of activation in mutant channels relative to wild-type (Sipos et al., 1995 Morrill and Cannon, 1999). Both effects are loss of function and could result in less calcium influx into the muscle cells during depolarizations. In... 

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). 

The a subunit is the most essential component of an ion channel. It is an integral membrane protein that requires a phospholipid environment to maintain a functional three-dimensional structure. Most a subunits are capable of forming functional channels when expressed alone in an artificial system, but they are often associated in native systems with transmembrane or cytosolic auxiliary subunits that modulate and fine-tune the properties of the channel. It is important to note that ion channel subunits often co-assemble in a tissue-specific manner and sometimes the expression patterns of individual subunits may be altered in disease. Therefore, when one is developing an assay using a heterologously expressed ion channel target, it is always preferable to employ a combination of subunits appropriate to the tissue and/or disease of interest. 

The N-alkylation reaction represents a bifurcation of the normal alkene epoxidation reaction cycle and, therefore, N-alkylation is a suicide event that leads to catalytic inhibition in the native system. With synthetic tetraarylporphyrins that mimic the N-alkylation reaction, the use of halogen-substituted catalysts that are stable toward oxidative degradation (26, 27) provide the most useful model systems because the heme model remains intact for a significantly greater number of turnovers than the partition number. The partition number is the ratio of epoxidation cycles to N-alkylation cycles, i.e., N-alkyl porphyrins are formed before the heme is oxidatively destroyed. 

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