IDENTIFICATION OF PROTEOLYTIC ACTIVITIES IN ROS-17 2.8 CELL LYSATES WHICH CLEAVE PEPTIDE-SUBSTRATES FOR PROTEIN-KINASE-C-MEDIATED PHOSPHORYLATION/

We have observed two proteolytic activities in cell lysates from the r at osteoblastic osteosarcoma cell line ROS 17/2.8 which are capable of cleaving a peptide substrate for protein kinase C-mediated phosphoryl ation, and other peptides containing similar sequences. Both activitie s are inhibited by Pefabloc, a serine protease inhibitor, while one of the activities is inhibited by either EDTA or aprotinin. The protease inhibitors pepstatin, bestatin, E-64, leupeptin and phosphoramidon do not block either of these proteolytic activities.