Changes in intracellular enzymes of collagen biosynthesis during matrix-induced cartilage and bone development

The activities of five intracellular enzymes of collagen biosynthesis were determined during cartilage and bone formation induced in rats by demineralized bone matrix. The five enzymes, prolyl 4-hydroxylase, prolyl 3-hydroxylase, lysyl hydroxylase, hydroxylysyl galactosyltransferase and galactosyl-hydroxylysyl glucosyltransferase, exhibited broadly parallel profiles; the activities rising steeply from day one to reach their highest values on day nine and decreasing gradually thereafter. The maximal enzyme activity correlated with the period of chondrogenesis and hypertrophic cartilage characterized by the synthesis of cartilage-specific type II collagen. Prolyl 4-hydroxylase was also studied in respect of its tissue distribution and cellular location using indirect immunofluorescence. The enzyme was mainly located in the mesenchymal cells on day three, in the chondrocytes and hypertrophic chondrocytes on days seven to nine, and in the osteoblasts on day eleven and thereafter.