170 The Biochemistry of Semen 



are given in Table 23, show a sharp increase in the choline content 

 of human semen during the first hour of incubation, and the rela- 

 tively slow accumulation during the next 47 hours; the terminal 

 decline is probably due to bacterial contamination. 



Enzymic liberation of choline froin precursors in semen 



Following up their observation that choline accumulates in semen 

 only after the ejaculation, Kahane and Levy demonstrated the pre- 

 sence in fresh semen of a 'precurseur de la choline' which yields free 

 choline as a result of hydrolysis which takes place in semen on 

 standing. Apart from the seminal plasma itself, they found the 

 choline precursor in various reproductive organs, including the 

 testis of bull, boar, ram, stallion, rabbit and guinea-pig, the seminal 

 vesicle of stallion and guinea-pig, and the epididymis of boar and 

 ram, but not the prostate of dog, stallion or ram. However, the 

 prostate, particularly that of dog, was found to be rich in the enzyme 

 which splits off choline from the precursor. In a series of studies, 

 Kahane and Levy (1938, 1945, 1949) have shown that the precursor 

 is a water-soluble compound ('choline hydrosoluble combinee') 

 which behaves like glycerylphosphorylcholine, and yields on incu- 

 bation with prostatic extracts a mixture of free choline and in- 

 organic phosphate; the quantity, however, of liberated choline was 

 found to be far in excess of the simultaneously appearing inorganic 

 phosphate. 



Phosphorylcholine and glycerylphosphorylcholine 



The nature of the phosphorus compounds in semen which yield 

 choline after ejaculation, was investigated by Lundquist (1946, 

 1947(7, b) and by Diament, Kahane and Levy (1952). 



In human semen deproteinized freshly with trichloroacetic acid, 

 the Danish investigator found 110 mg. acid-soluble P/100 ml, 

 including 10 mg./lOO ml. of inorganic phosphate. On neutraliza- 

 tion with barium hydroxide and precipitation with 2 vol. of ethanol, 

 he recovered 60-70% of the phosphorus in the filtrate and from this 

 he obtained by precipitation with mercuric chloride a fraction 

 containing nitrogen and phosphorus in a ratio of approximately 1:1. 

 The phosphorus compound thus separated was found to be very 



