22 The Biochemistry of Semen 



Compared with the prostatic fluid, the seminal vesicle secretion 

 is usually less acid, sometimes distinctly alkaline, has a higher dry 

 weight and contains more potassium, bicarbonate, acid-soluble 

 phosphate and protein; the latter is to a large extent precipitable by 

 trichloroacetic acid but there is also some 'proteose' as shown for 

 example, by the study of the seminal vesicle proteins in the goby 

 Gillichthys mirabiUs (Young and Fox, 1937). But the most remark- 

 able feature of the seminal vesicle secretion is its unusually high 

 content of reducing substances. 



The normal seminal vesicle secretion is usually slightly yellowish 

 but occasionally, especially in man and bull, it can be deeply pig- 

 mented. The yellow pigmentation is probably of composite origin 

 but much of it is due to flavins which cause the vesicular secretion and 

 seminal plasma to fluoresce strongly in ultraviolet light. Brochart 

 (1952) observed that when strongly yellow coloured samples of bull 

 seminal plasma are exposed to sunHght, the colour tends to dis- 

 appear within a short time and lumiflavin is formed. Leone (1953) 

 has shown that at least part of the flavin content of the bull seminal 

 vesicle secretion is due to adenine-isoalloxazine dinucleotide, 

 associated with xanthine oxidase. The highest content of total flavin 

 which I was able to record in the bull seminal vesicle secretion, was 

 750 /^g./lOO ml.; in eight samples of bull seminal plasma there was 

 from 47 yf^g./lOO ml. (in an almost colourless specimen) to 480 

 ^g./lOO ml. flavin (in a particularly deeply pigmented specimen). 

 There can be little doubt that the flavin associated with the strongly 

 yellow-coloured specimens of bull semen is due principally to the 

 seminal plasma, and not to the spermatozoa. The sperm cells them- 

 selves, however, contain also some flavin. In washed bull sperma- 

 tozoa, there is some 30 [ig. riboflavin/g. dry weight (Lardy and 

 Phillips, 1941c), and in whole bull semen, particularly in the less 

 coloured samples, a substantial portion of flavin may be derived 

 from the spermatozoa (VanDemark and Salisbury, 1944). 



In addition to the yellow pigment, the seminal plasma sometimes 

 contains a brownish haematin pigment; this occurs in cases of 

 'chronic haemospermia', a condition occasionally met with in man 

 and attributed to haemorrhagic changes in the seminal vesicles 

 (McDonald, 1946). 



Potassium in a high concentration occurs in the vesicular secretion 



