1 1 6 The Biochemistry of Semen 



semen and the prostate gland, and yielded the same amino acids 

 which appear normally in human semen. 



Pepsinogen 



Apart from the above mentioned protease which acts optimally 

 at pH 7-6, two more proteolytic enzymes have been found in 

 human semen by Lundquist and his co-workers (1951, 1952, 1953). 

 One is an amino peptidase which hydrolyses leucine amide, glycyl- 

 glycine, triglycine and glycyl- leucine, with an optimum around pH 

 7-5. The other has been identified as pepsinogen. According to 

 Lundquist and Seedorff (1952), the activity of pepsinogen in semen 

 corresponds to 2 //g. pepsin /ml., which is of the same order of 

 magnitude as that found in gastric juice. But unlike the trypsin- 

 like enzyme, seminal pepsinogen seems to originate in the seminal 

 vesicles and not in the prostate. Its specific function is not fully 

 understood as it is difficult to envisage in semen the high hydrogen 

 ion concentration required for the conversion of pepsinogen to 

 pepsin. 



Ammonia formation 



A phenomenon probably associated with the enzymic degrada- 

 tion of proteins, is the progressive accumulation of free ammonia 

 which takes place in whole semen and in seminal plasma, on anaero- 

 bic as well as aerobic incubation. This has been observed in several 

 species (Shergin, 1933; Mann, 1945^). In ram semen for example, 

 the content of free ammonia (estimated by vacuum-steam distilla- 

 tion in the Parnas-Heller apparatus) was found to increase from 

 1-3 mg. NH3-N/IOO ml. in fresh semen to 9-7 mg. NH3-N/IOO ml., 

 after 7 hr. incubation at 37°, under sterile conditions (Mann, 

 \9A5a). Ammonia formed in semen is in considerable excess of the 

 amount which could be derived from adenyl derivatives; the total 

 adenine amino-A'^ content of the semen as assessed enzymically 

 with heart muscle deaminase being only about 4 mg./lOO ml. in 

 fresh, and 3 mg./lOO ml. in incubated, semen. It is also unlikely to 

 originate from urea, since the content of urea in semen is not sig- 

 nificantly affected by incubation. 



