The investigation of the structure of collagen in growth process by X-ray analysis and electron microscopy

The structure of collagen in growth process has been investigated by X-ray analysis and electron microscopy using laying hen leg tendon collagen. On unstretching, the orientation of the band structure becomes better with age in birds younger than 4.5 months and is complete at ages above 4.5 months, whereas on stretching, the orientation is complete independent of age. This result suggests that the band structure may be complete by hatching. At approx. 4.5 months of age, the laying hen leg tendon collagen begins to harden from the lower end portion of the leg. On a macroscopic level, this hardening means that the collagen changes from the soft and flexible state to the rigid state. The higher-order structure of the hardened collagen consists of two domains: one is the domain in which the band structure remains, though it is not as clear as that of the collagen in the soft tendon, and another is the domain in which the band structure disappears and slender streaks having widths of 5-10 nm run along the fibril axis. It can be considered that this hardening might be caused by the increase of cross-links accompanied by calcification.