114 The Biochemistry of Semen 



in the seminal plasma may be of some importance to the sperma- 

 tozoa. It may be recalled that excessive dilution of semen exerts a 

 deleterious effect on spermatozoa and that this can be counteracted, 

 partly at least, by the inclusion in the diluting media of amino acids 

 such as glycine, alanine, valine, leucine, lysine, and glutamic acid 

 (p. 76). The beneficial action of these amino acids is believed to 

 depend primarily on their metal-binding capacity (Tyler and Roth- 

 schild, 1951). Several other effects of amino acids have been observed 

 with the sperm of lower animals. Giese and Wells (1952) found 

 that glycine (005m) protected the spermatozoa of Strongylocentrotus 

 piirpwatus from the detrimental effect of light. Metz and Donovan 

 (1950) demonstrated that in the starfish certain amino acids promote 

 the agglutination of spermatozoa by egg-water of this species; in 

 the absence of these amino acids agglutination does not take place. 



Fibrinolysin and fibrinogenase 



The seminal proteoses and amino acids are presumably the pro- 

 ducts of proteolytic activity which in the seminal plasma is derived 

 mainly from the prostatic secretion, but partly also from the 

 seminal vesicle fluid. The two powerful proteolytic agents of the 

 prostatic secretion are 'fibrinolysin' and 'fibrinogenase' (see also 

 pp. 17 and 29). 



The coagulation of human semen is followed by liquefaction, a 

 process which is catalysed by a proteolytic agent present in the 

 prostatic secretion. Its discoverers, Huggins and Neal (1942) named 

 it fibrinolysin because of its ability to digest blood fibrin, and its 

 resemblance to the fibrinolytic agent in haemolytic streptococci 

 (Tillet and Garner, 1933). However, the fibrinolytic system present 

 in blood has now been resolved into several distinct components, 

 whereas the streptococcal fibrinolysin has been defined as a kinase, 

 i.e. an activator of the fibrinolytic enzyme preformed in the blood. 

 Consequently, the name 'fibrinolysin' has been abandoned with 

 reference to the streptococcal agent in favour of 'streptokinase'. 

 Furthermore, it proved impossible to replace streptokinase by pro- 

 static fibrinolysin as an activator of the blood enzyme (Oettle, 

 1950). 



The fibrinolytic activity can be assayed in human semen by the 

 method of Harvey (1949), which consists in mixing a constant volume 



