Site bundling

As stated above, rail transports in chemical industry are often used for distribution of intermediate and basic chemicals with moderate demand. Often the transported chemicals serve as raw materials for other chemical plants which either belong to a customer s or the shipper s production network. Since rail transports require cargo consoUdation to operate economically efficiently, at large-scaled chemical production sites bundles of chemicals are handled. I.e. rail transports are a viable option even if the individual demands of each chemical cannot be shipped efficiently by rail. 

Automa-ticity. Special cardiac cells, such as SA and AV nodal cells, His-bundle cells, and Purkinje fibers, spontaneously generate an impulse. This is the property of automaticity. Ectopic sites can act as pacemakers if the rate of phase 4 depolarization or resting membrane potential is increased, or the threshold for excitation is reduced. 

Figure 8.22 The lac repressor molecule is a V-shaped tetramer in which each arm is a dimer containing a DNA-hinding site. The helix-tum-helix motifs (red) of each dimer bind in two successive major grooves and the hinge helices (purple) bind adjacent to each other in the minor groove between the two major groove binding sites. The four subunits of the tetramer are held together by the four C-terminal helices (yellow) which form a four helix bundle. The bound DNA fragments are bent. (Adapted from M. Lewis et al., Science 271 1247-1254, 1996.)...

The coiled-coil structure of the leucine zipper motif is not the only way that homodimers and heterodimers of transcription factors are formed. As we saw in Chapter 3 when discussing the RNA-binding protein ROP, the formation of a four-helix bundle structure is also a way to achieve dimerization, and the helix-loop-helix (HLH) family of transcription factors dimerize in this manner. In these proteins, the helix-loop-helix region is preceded by a sequence of basic amino acids that provide the DNA-binding site (Figure 10.23), and... 

The microtubule-associated proteins MAP2 and tau both have two separate functional regions (Lewis et al., 1989). One is the microtubule-binding site, which nucleates microtubule assembly and controls the rate of elongation (by slowing the rate of assembly). The second functional domain shared by MAP2 and tau is a short C-terminal a-helical sequence that can cross-link microtubules into bundles by self-interaction. This domain has some of the properties of a leucine zipper. Likely it is responsible for the organization of microtubules into dense stable parallel arrays in axons and dendrites (Lewis et al., 1989). 

In 1996, the 3D-structure of D. vulgaris Rr was published by de-Mare and collaborators 48), and all the studies earlier published were proved to be correct. The protein is described as a tetramer of two-domain subunits (Fig. 4). Each subunit contains a domain characterized by a four-helix bundle surrounding a diiron-oxo site and a C-terminal rubredoxin-like Fe(RS)4 domain (see Fig. 2). In this last do-... 

The ontogenesis of the AOS then, is closely bound up with the formation of its principal connection site within the mature brain. The sequence of events in mammals is revealed as a process which involves (1) early specialisation of presumptive GnRH cells (2) their attachment to and movement along specific (and transient) axonal bundles of the VN and N. terminalis tracts, and (3) coalescence of the neurocrine cells in the hypothalamus, where they complete differentiation as multi-axonal neurocrine cells. 

Heat exchangers need to be sited so that the tube bundles can be easily withdrawn for cleaning and tube replacement. Vessels that require frequent replacement of catalyst or packing should be located on the outside of buildings. Equipment that requires dismantling for maintenance, such as compressors and large pumps, should be placed under cover. 

In the x-ray structure of rhodopsin, an amphipathic helix runs parallel to the membrane from the intracellular end of TM-VII beneath the seven-helical bundle to the other side of TM-I and TM-II. At this point, one or more Cys residues are often found and are known to be subject to a dynamic posttranslational modification with palmitic acid residues. Like the phosphorylation event, the palmitoylation process appears to be dynamically regulated by receptor occupancy and is also involved in the desensitization phenomenon. The two posttranslational modifications can influence each other. For example, the conformational constraint induced by palmitoylation may alter the accessibility of certain phosphorylation sites. Like the phosphorylation process, the functional consequences of palmitoylation also appear to vary from receptor to receptor. 

L. inocua ferritin site however, is the first described so far that has ligands belonging to two different subunits, and is not contained within a four-helix bundle. Recently it has been suggested that the neutrophil-activating protein of Helicobacter pylori, the major antigen of the immune response in infected individuals, is also a dodecameric ferritin, capable of binding up to 500 iron atoms per oligomer (Tonello et ah, 1999). 

An important route to solubilization of carbon nanotubes is to functionalize their surface to form groups that are more soluble in the desired solvent environment. It has been shown that acid treatment of nanotube bundles, particularly with HC1 or HNO3 at elevated temperatures, opens up the aggregate structure, reduces nanotube length, and facilitates dispersion (An et al., 2004 Kordas et al., 2006). Nitric acid treatment oxidizes the nanotubes at the defect sites of the outer graphene sheet, especially at the open ends (Hirsch, 2002 Alvaro et al., 2004), and creates carbonyl, carboxyl, and hydroxyl groups, which aid in their solubility in polar solvents. 

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