Extracellular matrix vesicles from bovine fetal alveolar bone and from a dog osteosarcoma were isolated by differential centrifugation and then fractionated on a discontinuous sucrose density gradient. The fractions were examined by electron microscopy and were analyzed for protein, alkaline phosphatase, aminotripeptidase, and four different beta-naphthylamidase activities. The low-density peak of enzyme activities was shown by electron microscopy to be much more homogeneous than the crude matrix vesicle fraction. Two major peaks of protein and enzyme activities were present, one in the high and one in the low density layers. There was good correlation between the activities of alkaline phosphatase and the various peptidases in the fractions from the sucrose density gradient. These results indicate a coexistence of peptidase and alkaline phosphatase in matrix vesicles. On the other hand, there was generally no correlation between the peptidase and alkaline phosphatase activities in vesicular specimens from bovine liver obtained in the same way. Most of the peptidase activity and about half of the alkaline phosphatase activity were solubilized from bone matrix vesicles by detergents. The extracted alkaline phosphatase and alanyl beta-naphthylamidase activities were separated from each other on a DEAE-cellulose column.

Extracts of epiphyseal articular and costal cartilages and of metaphyseal bone showed different profiles of activity against 21 aminoacyl β-naphthylamides. Except for the activity against arginyl and lysyl j3-naphthylamides, most of the activities required the presence of Triton X-100 for extraction, suggesting that in situ, the enzymes are bound to or within membranous structures. Histochemical studies demonstrated that most, if not all, activity was intracellular. The activity is enhanced by Co^2+. TAME (2 X 10^-4 mol/1) inhibits activity against leucyl β-naphthylamide and some others, but has little, if any, inhibition of activity against alanyl β-naphthylamide. Gel filtration of the extract showed a high molecular weight active fraction eluting with proteoglycan, and an active fraction with an approximate molecular weight of about 230,000. Two active fractions are obtained by gradient elution from DEAE-cellulose.

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