Summary.-Ehrlich ascites cells in mice have been shown to have a cell-surface trypsin-like neutral protease (TLNP) with proteolytic and p-naphthylamidase activity. This activity is inhibited by low-mol.-wt inhibitors of trypsin but not by 11 high-mol. -wt inhibitors of trypsin in free solution. We believe this lack of inhibition is due to protection given to the enzyme by the chemical environment of the cell surface. These cells were demonstrated to export a collagenase zymogen which has been shown to be activated by the cell-surface TLNP. When this protease was completely inhibited by low-mol.-wt inhibitors of trypsin, chymotrypsin was used to activate the collagenase zymogen exported by Ehrlich ascites cells. Examination of the products of collagenolysis at 15°C demonstrated the expected 3-and 4-length a-chain fragments derived from monomeric collagen, confirming that collagenase was one of the enzymes responsible for lysis of the collagen fibrils in the test system.
Ehrlich ascites tumour cells grown in mice have a cell-surface trypsin-like neutral protease (TLNP) which is not inhibited by high-mol.-wt inhibitors of trypsin. This enzyme is inhibited by low concentrations of zinc, which may be removed by chelating agents, with the consequent return of enzymic activity. Gold, provided as the drugs aurothiomalate or auranofin, also inhibits TLNP. The gold can be removed from the enzyme by incremental addition of thiols. The mechanisms of gold transfer to the active site to cause inhibition and subsequent removal of gold with reactivation of TLNP, have been shown to be controlled by reversible thiol-exchange reactions.
Summary.-Previous studies have characterized the enzymatic properties and inhibition of a trypsin-like neutral protease on the surface of Ehrlich ascites cells by means of kinetic analysis. The present study links these kinetic studies with the recently reported role of a tumour-cell membrane-bound serine protease in tumourinduced target cell lysis. Low-mol.-wt inhibitors of this cell-surface trypsin-like neutral protease exhibited a corresponding ability to prevent tumour-induced haemolysis. High-mol.-wt inhibitors of trypsin in free solution had no inhibitory action either on the tumour-bound enzyme or on the ability of tumour cells to lyse erythrocytes. Fragments of tumour-cell membrane retain both the trypsin-like neutral protease activity and the ability for haemolysis. This study represents a correlation between an easily assayed membrane-bound enzyme on tumour cells and a function of possible biological relevance.
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