Studies on the Structure of Feather Keratin: I. X-Ray Diffraction Studies and Other Experimental Data

Previous data as well as new results are examined with a view to determining the boundary conditions which present experimental information places on a satisfactory polypeptide chain model for the structure of feather keratin. Our studies indicate these conditions to include the following: (1) A 189 A identity period, with a pseudoidentity of 94.5 A; (2) characteristic fiber axis periodicities of 23.6₄, A and 18.9 A; (3) a meridian reflection of 2.96 A, but none in the 1.0 A region; (4) a strong, but sensitive, equatorial reflection of about 33 A spacing, with a possible equatorial reflection near 50 A; (5) perpendicular infrared dichroism of v (NH) of at least 5:1; (6) a limited extensibility along the fiber axis direction; (7) the natural accommodation of about 12 per cent of proline residues in the structure; (8) the possibility of breaking down the structure into units of about 10,000 molecular weight. The implications of these conditions with respect to a satisfactory model are considered.