Stereochemical criteria for polypeptide and protein chain conformations

Part I. Evaluation of helical parameters
  • C. Ramakrishnan


A large number of configurations are possible for a polypeptide structure depending upon the relative orientations of the two peptide groups linked at anα-carbon atom. If the linkages at theα-carbon atoms are identical, then the structure assumes a regular helical form. Such a regular helical structure can be specified by two parametersφ, φ′ which are the angles of rotation of the two groups about the N—αC andαC—C′ bonds meeting at anα-carbon atom. In this paper, a method of evaluating the helical parameters of a structure, namely, the number of residues per turnn, the unit translation along the axis of the helixh and the direction cosines of the helical axis with respect to a suitably chosen co-ordinate system, is described making use of rotation matrices. The evaluation has been done for three different values of the angle\(N\widehat{aC}C'\) at theα-carbon atom, namely, 105°, 110° and 115°. The results are shown graphically in the form of curves for constantn and constanth in theφ − φ′ plane.


Dihedral Angle Direction Cosine Stereographic Projection Peptide Group Peptide Residue 


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Copyright information

© Indian Academy of Sciences 1964

Authors and Affiliations

  • C. Ramakrishnan
    • 1
  1. 1.Department of PhysicsUniversity of MadrasMadras-25

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