Remodelling of the Bone Matrix 



29 



It is interesting to consider such a difference in activity of enzymes depending on 

 the degree of polymerisation of the collagen. It can be related to the observation that 

 in soft connective tissues the degradation seems to occur from the pools of collagen 



Time dependence 



Concenfrafion dependence 



50 75 



Concentration 



Fig. 3. Concentration and time dependence activity of bacterial coUagenase (purified), tr\psiii (Calbiochem) and 

 pepsin (Calbiochem) on "C collagen fibers (S.A. 20.500 cpm/mg.). Results expressed in cpm liberated above blank 



which are the most easily extractable, the less organized. This form of collagen in- 

 creases in tissues having rapid degradation processes. This has been inferred from 

 studies in the metamorphosing tail of the tadpole (Lapiere and Gross, 1963) in the 

 uterus (WoESSNER and Brewer, 1963) and in the carrageenan granuloma (Jackson, 

 1957). In these resorbing tissues (Weber, 1957; Woessner and Brewer, 1963) and in 

 resorbing bone (Vaes, 1964) there is also an increased amount of acid cathepsins. 

 These enzymes could be involved in completing the breakdown of collagen after it is 

 phagocytised by specialised cells. Electromicrograph pictures of histiocytes containing 

 considerable amounts of fragmented fibrils have been shown to occur in the resorbing 

 tail of the tadpole (Usuku and Gross, 1965). Pictures having comparable meaning 

 have been published by Hancox and Boothroyd (1963) for the osteoclasts of 

 resorbing bone. 



On the basis of these different findings one might suggest that collagen degrada- 

 tion in soft and calcified tissues is a two step mechanism. In the first the collagen 

 matrix would be disorganized by an extracellular enzyme having collagenase activity. 

 Further activity of intracellular enzymes would complete the breakdown to liberate 

 free and peptide bound collagen aminoacids. 



Conclusion and summary 



Although much work is still needed before the metabolism of the bone matrix can 

 be understood, preliminary experiments indicate a close similarity with the meta- 

 bolism of the collagen in soft connective tissues. Synthesis, organization or enzymatic 

 breakdown are to a considerable extent analogous. 



