Configuration helical

Pauling, L., Corey, R.B., Branson, H.R. The structure of proteins two hydrogen-bonded helical configurations of the polypeptide chain. Proc. Natl. Acad. Sd. USA 37 205-211, 1951. 

Rotary, positive displacement machines in which two intermeshing rotors, each in helical configuration displace and compress the air available in lubricated and non-lubricated construction the discharge air is normally free from pulsation high rotation speed. 

The flow through helically configured, round tubes was first examined by Eustice (12) in 1910 and the first theoretical analysis was published by Dean in 1927 and 1928 (13). He showed that the fluid flow could be characterized by the dimensionless group... 

Figure 3-4. Dimensions of a fully extended polypeptide chain. The four atoms of the peptide bond (colored blue) are coplanar. The unshaded atoms are the a-carbon atom, the a-hydrogen atom, and the a-R group of the particular amino acid. Free rotation can occur about the bonds that connect the a-carbon with the a-nitrogen and with the a-carbonyl carbon (blue arrows). The extended polypeptide chain is thus a semirigid structure with two-thirds of the atoms of the backbone held in a fixed planar relationship one to another. The distance between adjacent a-carbon atoms is 0.36 nm (3.6 A). The interatomic distances and bond angles, which are not equivalent, are also shown. (Redrawn and reproduced, with permission, from Pauling L, Corey LP, Branson PIR The structure of proteins Two hydrogen-bonded helical configurations of the polypeptide chain. Proc Natl Acad Sci U S A 1951 37 205.)...

Second, our studies of the secondary structure of the H" "-ATPase indicate that about 36% of the polypeptide chain is present in a helical configuration [27,42]. If the membrane-embedded sector of the molecule is helical as shown, only 90 or so additional residues in the molecule can be present as helices. Thus, the great majority... 

Figure 5.4 Structure and manner of assembly of a simple virus, tobacco mosaic virus, (a) Electron micrograph at high resolution of a portion of the virus particle, (b) Assembly of the tobacco mosaic virion. The RNA assumes a helical configuration surrounded by the protein capsomeres. The center of the particle is hollow.

Pauling, L. and Corey, R. B. (1951), Atomic coordinates and structure factors for two helical configurations of polypeptide chains , Proceedings of the National Academy of Sciences (USA),... 

The atropisomerization of the helical configuration entails movement of the C2, C2 - and C7,C7 -groups past one another (Fig. 7.1), and the barrier to this isomerization varies substantially for the different perylenequinones. While the calphostins (4) and phleichrome (5) are atropisomerically stable at room temperature and require temperatures over 110 °C to isomerize, the additional seven-membered ring bridge at the C2,C2 -positions in cercosporin (3) lowers the barrier allowing it to atropisomerize at 37 °C [34]. 

In case of sufficiently strong antiferromagnetic NNN interactions compared to the NN ones, that is, 2(5 + 5 ) > 1 with 5 = /2 S2//1Ss and S = / s2//jSs, the ground state in zero static field has a helical configuration of the spins, as shown in Figure 4.6a, with the angle between adjacent spins, 0, defined as ... 

Aggregated helices helical configuration linear configuration ... 

Dombrow and Beckmann163 have carried out ultracentrifugal and viscometric studies of several amylose acetates in methyl acetate solution. Their data, shown in Table VI, were interpreted as supporting the idea of a helical configuration in solution. 

From measurements of the dichroism of flow of amylose-iodine solutions,161 and from studies of the optical properties of crystalline amylose platelets and iodine-stained platelets,163 it was shown, following the suggestion of Hanes, that a helical configuration of the amylose in this complex is probable. This was later confirmed by x-ray measurements (see p. 378) the iodine atoms were shown to be situated in the core of helically-oriented amylose molecules. 

In addition, Zn2+ was shown to inhibit dopamine uptake in a mutant containing an engineered tridentate zinc site, in which the i-4 site from His3757.60, Met3717.56, was replaced with histidine, whereas the introduction of histidines at the i-2, i-3, and i-5 position did not increase Zn2+ affinity (29). In contrast, histidines at positions i+2, i+3, and i+4 all resulted in potent inhibition of dopamine uptake by Zn2+. The incorporation of these data in a model of secondary structure provides evidence for an a-helical configuration of the extracellular portion of TM7, as well as the absence of well-defined secondary structure between positions 3757.6o and 37 97.64 (Fig. IB), thereby suggesting an approximate boundary between the C-terminal end of the helix and the beginning of EL4 (29). 

Infrared and circular dichroism (CD) measurements (Moss et al., 1976b) are both consistent with a sizable fraction of the tetramer being in the a-helical configuration, —29% a-helix with negligible j3 structure. This is rather similar to the 25% a-helix and —0% /3 structure obtained for the tetramer prepared from acid-extracted histones (D Anna and Isenberg, 1974b). 

The close correspondence of the DNA absorption spectrum with that of a mixture of mononucleotides of the same composition illustrates the weak nature of the interactions between neighboring purine and pyrimidine bases guanine (G), cytosine (C), adenine (A), and thymine (T) at an interplanar separation of 3.36 A in the unexcited double-helical configuration. On the other hand the structureless fluorescence band of (calf-thymus) DNA is red-shifted by 3500 cm-1 from the fluorescence spectral origin of the mononucleotides it closely resembles the fluorescence spectrum of the dinocleotide ApT (and of poly dAT) and is accordingly identified131 with the fluorescence... 

Fig. 16.7. Structure of the postulated voltage sensor in the S4 helix. The S4 segment of the K channel is shown in an assumed helical configuration with the individual amino adds given as one-letter codes. The regular sequence of a basic amino add and two hydro-phobic amino acids is characteristic for the S4 segment. The basic amino adds are numbered from the N to the C terminus. According to Catterall, (1995) with permission.

Fig. 1. The steric protection of the carbon backbone by fluorine of a polytetrafluoro-ethylene chain. The helical configuration of fluorine with a repeat distance of 16.8 A (--------) results from the steric crowding of adjacent fluorine.

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