Cathepsin B and L activities in isolated osteoclasts.

Cathepsin B and L activities were examined with chicken osteoclasts isolated by sequential filtration and inhibitors were added to disaggregated rat osteoclasts on cortical bovine bone. Z-Phe-Phe-CHN2, a selective inhibitor of cathepsin L, at 1, 5, and 10 microM, inhibited bone resorption by rat osteoclasts 50, 85, and 100 per cent and, in chicken osteoclasts, cathepsin L activity was comparably inhibited. Cathepsin L in avian osteoclasts was also 25-fold higher than cathepsin B. Chicken osteoclasts treated with Z-Phe-Ala-CHN2, a generalized cysteine proteinase inhibitor, had both cathepsins inhibited to the same extent. Cathepsin L may play a key role in resorption.