188 The Biochemistry of Semen 



with the general chemical properties of accessory gland secretions 

 (p. 19) concerns the high transaminase activity in the human pros- 

 tate as well as in the rat ventral prostate, both of which secrete 

 citric acid. The considerable transaminase activity together with the 

 occurrence of free amino acids, including glutamic acid, in these 

 two glands, point to the possibility of citric acid being formed from 

 oxaloacetic acid which arises from glutamic acid as a result of 

 transamination (Barron and Huggins, 1946o; Awapara, 1952a, b\ 

 Awapara and Scale, 1952). 



As to its physiological role in semen, the available evidence does 

 not support the view that citric acid influences markedly the aerobic 

 or anaerobic metabolism of spermatozoa (Humphrey and Mann, 

 1949); thus the beneficial effect of citrate on sperm motility ob- 

 served by Lardy and Phillips (1945) may be due to a cause other 

 than direct utilization by sperm. It is conceivable that citric acid 

 is connected with the coagulation and liquefaction of semen and 

 with the calcium-binding capacity of seminal plasma. In this con- 

 nection one may recall the finding of Huggins and Neal (1942) 

 that citrate in human semen causes prolonged coagulation of mix- 

 tures of blood and seminal plasma, and that this delay in clotting 

 can be effectively counteracted by calcium ions. The function of 

 citric acid as a binding substance for calcium has been envisaged 

 both by Schersten (1936) and Huggins (1945) and it is certainly sig- 

 nificant that milk and bones, both rich in citrate, also have a high 

 calcium content. Perhaps in the absence of citric acid in the prostatic 

 secretion, there would be an even higher incidence of calculi and 

 stones. The possibility of a link with the hyaluronidase activity 

 cannot be excluded, as indicated by Baumberger and Fried (1948) 

 who found that citrate exerts a protective action against so-called 

 antinvasin in vitro. Lundquist (1947Z?), however, believes that citrate 

 may act as an activator of the prostatic 'acid' phosphatase. Lastly, 

 let it be remembered that citric acid, in combination with potassium 

 and sodium ions, may play a part in maintaining the osmotic 

 equilibrium in semen. Our own studies on the boar vesicular secre- 

 tion (Mann, 1954) point in this direction. 



