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 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


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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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