Structure of collagen

Abstract

A detailed X-ray study of collagen fibres obtained from different sources (namely, shark ray, rat tail tendon and kangaroo tail tendon) and a re-examination of the published wide-angle patterns indicate that the unit cell of collagen is hexagonal with a = 12-16 A. and c = 9.5-9 A., the actual values depending on the moisture content. The essential difference of this indexing from those reported earlier is that the 2.86-A. meridional arc is here interpreted not as a true meridional reflexion, but as arising from the superposition of two close non-meridional reflexions. A calculation of the angular spread of the arc, using the tilt of the c-axis deduced from the spread of the equatorial reflexions, confirms this interpretation. Table 1 shows the good agreement between the calculated and observed spacings of an air-dried and a wet specimen from kangaroo tail tendon.