Dermatan sulphate, hydroxyproline and collagen fibril diameters were measured in flexor tendons from chick and calf limbs, from early in embryonic development to maturity. The collagen fibril is viewed as a long thin cylinder. A species X present at the periphery of the cylinder, regularly and specifically arrayed along the fibril, should then satisfy the relationship [X]/[collagen]r = k where [X] and [collagen] are tissue concentrations of X and collagen, and r is the fibril radius. Throughout the developmental period studied, dermatan sulphate (i.e.X) in chick, calf and rat tendons fits the relationship, implying that it is specifically, regularly and entirely associated with collagen fibrils, thus confirming and extended previous electron histochemistry [Scott & Orford (1981) Biochem. J. 197, 213-216]. This approach explains the pattern of change of dermatan sulphate content during development of the tendon. The findings imply that the dermatan sulphate proteoglycan-collagen interaction is evolutionarily highly conserved. The relationship [X]/[collagen]r = k is used to show that surface concentrations of covalently bound species, such as extension propeptides, can be easily assessed, given the data base described in paragraph 1 above.

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