AGGREGATE DEGRADATION BY GROWTH-PLATE PROTEASES

For long bone growth to occur, calcification of the matrix must begin in the lower hypertrophic zone of the growth plate. It generally is ac cepted that physeal proteoglycans help regulate mineralization, and th at, at least in vitro, smaller proteoglycan fragments are less inhibit ory of mineral formation. It also has been shown that proteoglycan deg rading enzymes are concentrated in the hypertrophic zone, where calcif ication occurs, Thus, one can hypothesize that these enzymes ape invol ved in the calcification process. Proteoglycans appear mainly as the a ggregate form in the physis, and this study demonstrates the ability o f the naturally occurring physeal enzymes to degrade proteoglycan aggr egate, without first disaggregating it. Because the matrix constituent s probably limit hypertrophic cell size and shape, this degradation ma y have some relationship to the rate of growth of the physis.