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Optical activity of polypeptides and proteins
Author(s) -
Madison Vincent,
Schellman John
Publication year - 1972
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1972.360110509
Subject(s) - polyproline helix , chemistry , circular dichroism , globular protein , helix (gastropod) , lysozyme , myoglobin , crystallography , ribonuclease , protein secondary structure , protein structure , biophysics , biochemistry , peptide , rna , ecology , snail , gene , biology
Using methods described in a previous publication the optical activity of a number of polypeptides and proteins has been calculated. The systems included the α‐helix, the two β‐structures, polyproline I, polyproline II, collagen and collagen models, and poly‐ N ‐methylalanine. In addition to these orderded structures, calculations were also performed on the α, β and nonperiodic regions of myoglobin, lysozyme, ribonuclease‐S and β‐chymotrypsin. The α and β structures in prteins differ from the polypeptide models by being very short and partially disordered. It is concluded that the 222‐nm band of the α‐helix is a good method for detecting helices in proteins but that the 207‐and 191‐nm bands of the helix will not fit a linear superposition model. The circular dichroism of the so‐called β regions of proteins differs markedly from that for ideal β structure because of breakdownin symmetry. As a result estimates of β‐structure in proteins based on polypeptide models are not likely to be quantitative. The theoretical methods give an adequate account of the optical activity of all the ordered polypeptides except polyproline II and collagen and (by inference) the nonperiodic chains in the various proteins. This difficulty is the remaining barrier to a complete theory of the optical activity of the polypeptide backbone in globular proteins.