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Secondary module orientation

Terms such as stolon, primary and secondary stem, and branch, have often been used without careful attention to the role of the apical cell in formation of each of these features. Consequently, a primary stem in one taxon may equate to a stolon in a second, and a branch in a third, while a secondary stem may be the continuation of the primary stan but with a different orientation, a new primary module, or a secondary module (a branch ). This lack of clarity reduces the information content of these terms and makes structural comparisons between taxa difficult or meaningless, especially for determination of homology in cladistic analysis. [Pg.290]

Although both IFN-7 and lL-10 swap the same secondary structural elements (helices E and F) to form the dimers, their quaternary structures are very different. IFN-7 and lL-10 adopt inter-domain angles of approximately 60° and 90°, respectively. More recently, the structure of cmvIL-10 revealed a domain angle of approximately 150° (Jones et al, 2002b). In addition, the two cmvIL-10 peptide chains form an interchain disulfide bond while IFN-7 and cellular IL-10 are non-covalent dimers. The domain orientations of each dimer are essentially fixed at one unique inter domain angle which alters the orientation of the cell surface receptors and may ultimately modulate cellular signal transduction events. [Pg.188]

Secondary effects can introduce small errors in this method of measuring twist. Dust and surface scatches can, of course, seriously affect local alignment. More subtle are perturbations apparently produced by variations in the flow pattern (hydrodynamic domains) of neutral molecules. In the cells used here hydrodynamic instabilities become quite pronounced at field frequencies around 5 Hz at 17v and resemble the patterns described by Sussman.9 They were not visible at 0.3 Hz and 17v but Fig. 11 shows evidence of their presence. In this case, the 0 orientation of the cell was fixed and the cell was translated relative to the beam while applying 17v at 0.3 Hz. A slow variation in polarity modulation amplitude is expected because of the effects discussed in connection with Fig. 3. Superimposed are local oscillations of modulation amplitude possibly attributable to hydrodynamic domains. It may be surprising that neutral molecule flow would not exhibit a more pronounced effect however, the flow adjacent to the cell walls must be parallel to the walls and exert a minor orienting force on the thin layer of molecules with significant homogeneous component at 17v. [Pg.151]

The importance of secondary interactions in modulating the chemistry of a metal-bound water or hydroxide moiety has been discussed for metaUoenzymes of varying function [42, 43). For example, in zinc-containing carbonic anhydrase II, the zinc-bound hydroxide acts as a H-bond donor to a threonine residue (Thrl99 Fig. 8.7) [37]. This interaction orients the lone pair of the hydroxide and reduces the entropic barrier for catalysis [44]. Notably, perturbation of this H-bonding interaction is reported to increase the Zn-OH2 pJCa value by around 2 units [45]. The threonine residue also stabilizes the transition state via H-bonding and destabilizes the product (bicarbonate-bound) form of the enzyme. It is also interesting that an X-ray diffraction study of crystals of carbonic anhydrase II isolated at pH 7.8 revealed two water molecules that donate H-bonds to the zinc-bound hydroxide (Fig. 8.7) [46]. [Pg.293]


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Secondary module

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