An assay measuring the release of TCA soluble radioactive peptides from 3H acetylated casein or hemoglobin has been used to demonstrate that human peripheral blood lymphocytes contain a number of proteases, including cathepsin D, a neutral serine protease(s) inhibited by DFP and TLCK and probably a thiol protease(s) as well. We have also found a neutral protease activity bound to the surface of the lymphocyte, but not secreted into the medium which is not inhibited by TLCK. TLCK inhibits blast transformation to PHA under conditions that do not profoundly affect protein synthesis and inhibits the total extractable proteolytic activity of lymphocytes by approximately 25%. Lymphocytes contain one or more proteases that may play a role in blast transformation and other lymphocyte functions.
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