264 IMMUNO-CATALYSIS 



brin or serum clot has generally been known as serum tryptase or serum 

 protease. Since serum proteolytic enzyme has been found, in some 

 respects, to differ from the usual trypsin, the use of the term serum 

 protease would seem to merit more serious consideration. Christensen 

 (1945, 1946) and Christensen and MacLeod (1945) have proposed 

 the name flasmin, and Loomis, George and Ryder (1947) fihrinolysin. 

 The former term appears to account for the properties and the origin 

 of the serum enzyme, the latter term is too confined in its scope for 

 the reason that serum enzyme is capable of digesting also gelatin, 

 casein, hemoglobin and fibrinogen. The normal inactive state of serum 

 protease has been called 'plasminogen (Christensen, 1946), and pro- 

 fihrinolysin (Loomis, et at., 1947). These names convey, according to 

 our present knowledge and understanding, erroneous meaning. The 

 chemical reactions involved in the conversion of the inactive state of 

 serum protease into the active state, and our critical information con- 

 cerning the chemical structural and origin of the inactive form of this 

 enzyme exist, as yet, in a state inadequate to justify the adoption of 

 these terms here. Christensen (1945) attributes to the bacterial factors 

 (fibrinolysins) a kinase role in fibrinolysis, and Loomis et at. (1947) 

 have named it streptokinase. For experimental reasons as discussed 

 below, the introduction of these terms would seem to be premature. 

 The term streptokinase is particularly unfortunate for the same reason 

 and also for the reason that many other species of bacteria have been 

 reported to elaborate the same or similar factors. 



It would, therefore, seem desirable that, at present, the adoption of 

 such terms be deferred until our understanding of the basic reactions 

 and the specific enzymes involved in blood clotting and lysis of the 

 products are more specifically characterized. We therefore find it ex- 

 pedient to use here the term fihrinolysis for the process which involves 

 the digestion of blood clot or fibrin; serum protease for the enzyme 

 which catalyzes fibrinolysis, since it is a proteolytic process; and the 

 substances which are derived from various bacteria capable of con- 

 tributing to fibrinolysis as hacterial fibrinolytic factors, or, merely, the 

 term hacterial factors to be used solely in conjunction with fibrinolysis. 



b. Digestion Products of Fibrin and Fibrinogen. Information is 

 lacking concerning the specific question of whether the lysis of fibrin 

 occurs because of the opening of the primary bonds (see section on 

 Thrombin) which were formed during the conversion of fibrinogen to 



