Protein Constituents and Enzymes of Seminal Plasma 1 1 5 



of oxalated blood plasma with varying volumes of semen, inducing 

 clotting by the addition of 1-5% calcium chloride, and noting the 

 time required for the clot to liquefy. Owing to the inhibitory effect 

 of blood plasma on fibrinolysis, the plasma must not constitute 

 more than one-tenth of the reacting system. Harvey states that the 

 degree of fibrinolytic activity in semen varies with the individual 

 but she found no correlation between this activity and either the 

 volume of ejaculates or any characteristics of spermatozoa. Simi- 

 larly, there was no positive relationship between the lysin content 

 and semen viscosity. However, specimens which were exceptionally 

 viscous, usually also had low fibrinolytic power. 



The precise nature of seminal fibrinolysin and its relation to 

 plasmin, the fibrin-splitting agent of the blood, will not be known 

 until the enzyme has been purified. Moreover, experiments by Kaulla 

 and Shettles (1953) indicate that in addition to the plasmin-like 

 enzyme proper, the human seminal plasma contains at least three 

 other agents, (i) fibrinolysokinase, an activator of blood profibrinoly- 

 sin, (ii) a small amount of profibrinolysin itself, i.e. of material 

 which can be activated by streptokinase, and (iii) antifibrinolysiny 

 an inhibitor of plasmin, which, however, is present in a much lower 

 concentration in the seminal plasma than in blood serum. 



Fibrinogenase is the name given by Huggins and Neal (1942) 

 to the proteolytic agent, highly active in canine prostatic secretion, 

 but less so in human prostatic fluid, which destroys blood plasma 

 fibrinogen. Huggins and his co-workers (1942, 1943) also share the 

 credit for having recognized the similarity between certain other 

 proteolytic properties of the prostatic secretion and those of pan- 

 creatic trypsin. More recently, the 'tryptic' enzyme of human semen 

 has been partially purified by Lundquist (1952), who defined as a 

 unit the amount of enzyme which in 1 hr., at pH 7-6, and 37°, 

 liberates from added casein a quantity of chromogen corresponding 

 to 01 mg. free tyrosin; he achieved an activity of about 1 unit per 

 mg. of protein-nitrogen, i.e. an approximately tenfold purification. 

 The purified enzyme was active also towards haemoglobin and both 

 human and bovine blood plasma fibrinogen. In an attempt to 

 purify from human semen the natural substrate for the proteolytic 

 activity, Lundquist obtained a protein fraction, 'seminal fibrin', 

 which was readily digested by enzyme preparations both from 

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