Assays of type I procollagen domains and collagen fragments: problems to be solved and future trends

The biochemical possibilities for developing specific assays for type I collagen metabolism are described. Type I collagen synthesis can be assessed either by the analysis of the carboxyterminal or aminoterminal propeptides, which are in principle produced in a molar ratio of 1:1. However, in clinical situations altered behaviour can be found, the reasons for which may be altered clearance or even the existence of variant forms of type I collagen. Type I collagen degradation can be specifically detected by analysis of either cross-linked carboxy- or aminoterminal telopeptides or by the cross-links themselves liberated during the degradation processes. The heterogeneity of the cross-links and the constituent chains of the cross-linked peptides in different tissues and possibly in different clinical situations introduce problems, which should be studied and resolved in the future.