23 1o cv n 120 120o communicated february 28 1951

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Unformatted text preview: nied along the axis. Hence the only configurations for a chain h our postulate of equivalence of the residues are helical For rotational angle 1800 the helical configurations may simple chain with all of the principal atoms, C, C' (the ), N, and 0, in the same plane. hat, because of the resonance of the double bond between en and carbon-nitrogen positions, the configuration of each residue IZ i.23 1o CV/ N 120° 120O Communicated February 28, 1951 CHEMISTR Y: PA ULING, COREY, BRA NSON 207 During the past fifteen years we have been attacking the problem of the structure of proteins in several ways. One of these ways is the complete and accurate determination of the crystal structure of amino acids, peptides, and other simple substances related to proteins, in order that information about interatomic distances, bond angles, and other configurational parameters might be obtained that would permit the reliable prediction of reasonable configurations for the polypeptide chain. We have now used this information to construct two reasonable hydrogen-bonded helical configurations for the polypeptide chain; wte think that it is likely that these configurations constitute an important part of the structure of both fibrous and globular proteins, as well as of synthetic polypeptides. A letter announcing their discovery was published last year. ' The problem that we have set ourselves is that of finding all hydrogenbonded structures for a single polypeptide chain, in which the residues are >N-C6 is planar. This structural feature has been verified for each of the amides that we have studied. Moreover, the resonance theory is now so well grounded and its experimental substantiation so extensive that there can be no doubt whatever about its application to the amide group. FIGURE 2 The helix: with 3.7 residues per turn. FIGURE 3 The helix with 5.1 residues per turn. Sequence affects α helix stability •  NegaHvely charged AA: omen...
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This test prep was uploaded on 02/25/2014 for the course BIOC 462A taught by Professor Ziegler,baldwin during the Spring '08 term at University of Arizona- Tucson.

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