Terminator complexes

Phosphinidenes differ from carbenes because of the additional lone pair. This lone pair enables interactions with, e.g., a transition metal group for increased stability, while maintaining carbene-hke behavior. These terminal /] -complexed phosphinidenes differ from the p2-> fi3-> and p4-complexes, which are not part of this survey. Phosphinidenes that are stabilized by a transition metal group also relate to carbene complexes. A distinction in Fischer and Schrock-type complexes has been advanced to distinguish phosphinidene complexes with nucleophilic properties from those that are electrophiHc [ 13 ]. In this survey we address this topic in more detail. 

The ribosome recycling factor (RRF) is a 21 kDa protein which is involved in the termination step of protein biosynthesis and catalyses the breakdown of the post termination complex into ribosome, tRNA and mRNA. The solution structure of RRF from the hyperthermophilic bacterium Aquifex aeolicus (7 opt = 85°Q was determined by heteronuclear multidimensional NMR spectroscopy, whereas the backbone NMR assignment was recently carried out for RRF from Themotoga maritima and Thermus thermophilus ... 

The Terminal Complex Hypothesis and Its Relationship to Other Contemporary Research Topics... 

The terminal complex hypothesis proposes that the cellulose synthesizing enzyme complex can be visualized with electron microscopy. Terminal complex is the name given to collections of plasma membrane particles thought to represent the cellulose synthase. While direct evidence is still not available to support this hypothesis, the amount of indirect supporting evidence has grown dramatically in the past few years. The relationship between terminal complexes, cellulose physical structure and the biochemical events of cellulose biosynthesis will be discussed. 

The terminal complex hypothesis proposes that structural manifestations of the cellulose synthase enzyme complex can be visualized with the freeze fracture specimen preparation technique for electron microscopy. These... 

Direct microscopic evidence demonstrating that terminal complex particles are cellulose synthesizing enzymes is not currently available and will await the production of antibodies against cellulose synthase following its isolation and purification. However, the proposal that terminal complexes are part of the cellulose synthase complex is increasingly becoming accepted... 

The identification of terminal complexes in the Gram-negative bacterium Acetobacter xylinum now appears to be in doubt. Previously, a single linear row of particles observed on the outer lipopolysaccharide membrane... 

PF had been proposed as the terminal complex (23) and associated pores were reported on the outer membrane EF (24). Due to their proximity to the site of cellulose ribbon extrusion from the cell surface, these structures were assumed to be responsible for cellulose synthesis. A model was advanced in which cellulose synthase was localized on the outer membrane, which invoked adhesion sites between the outer and plasma membranes as a mechanism to explain the transfer of uridine-diphosphoryl-glucose (UDPG) from the cytoplasm to the cellulose synthases (25,26). However, when the outer and plasma membranes of Acetobacter were isolated separately by density-gradient centrifugation, the cellulose synthase activity was localized only in the plasma membrane fraction (27). Therefore, the linear structures observed on the Acetobacter outer membrane, while they may be associated in some manner with cellulose biosynthesis, are probably not the cellulose synthase terminal complexes. Since no ultrastructural evidence for adhesion sites between the outer and plasma membranes has been presented, a thorough investigation of the mechanism of / (1-4) glucan chain translocation from the cytoplasmic membrane to the outer membrane in Acetobacter xylinvm is now in order. 

Terminal complex consolidation has also been reported in vascular plants as loosely aligned files of rosettes associated with secondary wall formation (13,14,34,35). Similar rosette files were also observed during primary wall formation in rapidly elongating regions of Avena coleoptiles... 

Consolidation of linear terminal complexes. The correlation between linear consolidation of terminal complexes and microfibril width does not appear to be as consistent for linear terminal complexes, although this correlation... 

In both genera terminal complex linear consolidation was reported to increase during primary wall formation, reaching a maximum length as secondary wall formation commenced. Similar results also were observed in Boodlea (Siphonocladales) during primary and secondary wall formation... 

Thus, linear terminal complex consolidation appears to be a manifestation of the stage of cell wall development rather than a significant factor in the determination of microfibril dimensions. 

Klaholz BP, Pape T, Zavialov AV, Myasnikov AG, Orlova EV, Vestergaard B, Ehrenberg M, van Heel M (2003) Structure of the Escherichia coli ribosomal termination complex with release factor 2. Nature 421 90-94... 

This is the terminal complex in the electron transport chain, which transfers electrons to oxygen, reducing it to water (Fig. 7.68). Cyanide binds to the Fe3+ form of iron (Fig. 7.69), which is found in cytochromes such as cytochrome a3, which undergo redox cycling. Thus, oxidized hemoglobin, cytochrome P-450, and cytochrome c are all targets. However, the effects on the mitochondria are the most significant because of the rapid effects on cell metabolism. 

Cellulose synthesis takes place in terminal complexes (rosettes) in the plasma membrane. Each cellulose chain begins as a sitosterol dextrin formed inside the cell. It then flips to the outside, where the oligosaccharide portion is transferred to cellulose synthase in the rosette and is then extended. Each rosette produces 36 separate cellulose chains simultaneously and in parallel. The chains crystallize into one of the microfibrils that form the cell wall. 

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