Proteolytic activities associated with plasma membrane preparations from tumour cells in enzootic bovine leukosis and from normal bovine lymphoid cells.

Proteolytic activities associated with plasma membrane preparations from cells of tumourous lymph nodes in enzootic bovine leukosis and from normal bovine lymphoid cells have been studied. 125I-Casein-Sepharose has been used as a substrate. No significant difference between both cell types has been found in total proteolytic activity at different pH-values as well as in the number and type of proteinases, the membranes seem to be equipped with. The main proteolytic activities present in both types of membranes are: One (or two) pepstatin-inhibitable aspartate-proteinase(s) with maximum activity at pH 3 and 5, a leupeptin-inhibitable, presumably cysteine-proteinase, maximally active at pH 4, very small activity(ies?) between pH 7 and 8 of uncertain nature, and a plasminogen-activator with maximum activity around pH 8. Autodigestion of plasma membranes from normal lymph node lymphocytes has been performed choosing conditions optimal for the different proteinases. The only specific proteolysis observed is the splitting of a glycoprotein (151.5 kD), which is present in the plasma membranes of normal lymph node lymphocytes but not in the plasma membranes of peripheral blood lymphocytes and tumour cells, under conditions optimal for the aspartate-proteinase. A possible role of this specific proteolysis is suggested for tumouri-genesis and/or loss of sessility of normal lymphocytes.