A fibrinolytic acid proteinase in human plasma

Abstract

An attempt has been made to purify an acid proteinase from human plasma, which is capable of dissolving fibrin clot in 1% (w/v) monochloroacetic acid. On SDS gel electrophoresis the enzyme isolated from plasma contains two protein bands with molecular weights of approximately 90,000 and 54,000. Different substrates were used to evaluate the proteolytic activity of the plasma enzyme, including fibrin clot, azo-casein, acid denatured haemoglobin (Hb), haemoglobin polyacrylamide gel (insoluble Hb), haemoglobin electrophoresis (soluble Hb) and the synthetic substrate N-acetyl-L-phenylalanyl-L-diiodotyrosine. The plasma enzyme seems to belong to the group of aspartyl proteinases as its activity against the above substrates was maximal at low pH, and was inhibited by pepstatin which is a powerful inhibitor of aspartyl proteinases.