1 50 The Biochemistry of Semen 



fructose, such as 6-phosphofructofuranose (Neuberg ester) and 1 : 6- 

 diphosphofructofuranose (Harden- Young ester), are formed as in- 

 termediary substances in the normal carbohydrate metaboUsm of 

 muscle, liver and other animal organs. However, in the majority 

 of animal tissues these phosphofructoses do not yield free fructose 

 but are metabolized further to form pyruvic acid and lactic acid. 

 In the semen, however, there are present in high concentration 

 enzymes which belong to the group of phosphatases and include 

 the 'alkaline' phosphatase; the latter capable of splitting a number 

 of phosphohexoses, including 6-phosphofructose, 1-phosphofructose 

 and 1 : 6-diphosphofructose, to phosphoric acid and free fructose. 

 The alkaline phosphatase found in semen is derived from several 

 accessory organs of reproduction but its principal source in higher 

 animals is the seminal vesicle. Owing to this fact, the usual channels 

 of carbohydrate metabolism are diverted in the vesicular tissue: 

 phosphofructoses are not metabolized to lactic acid, as would be 

 the case e.g. in muscle, but are dephosphorylated instead, so that 

 free fructose is formed. 



In extracts made from bull seminal vesicle tissue it is possible to 

 demonstrate the following reactions. When 1-phosphoglucose is 

 incubated, 6-phosphoglucose is formed through the action of phos- 

 phoglucomutase; next, part of 6-phosphoglucose is converted by 

 phosphohexose isomerase into 6-phosphofructose. The equilibrium 

 mixture of the two 6-phosphohexoses is acted upon by phosphatase 

 and yields a mixture of free glucose and free fructose. Phosphohexose 

 isomerase, together with alkaline phosphatase is also present in the 

 seminal vesicle secretion and seminal plasma. Ram seminal plasma 

 in particular, is a rich source of phosphatase active towards phos- 

 phorylated sugars (Table 17, p. 120). 



The fact that whereas a mixture of glucose and fructose is the 

 result of the phosphatase activity in the glandular tissue, yet, only 

 one sugar, that is fructose, accumulates in the secretion, may have 

 its explanation in a more effective re-utilization of glucose than 

 fructose, by the glandular tissue itself. Thus, we have found that 

 tissue slices from the rat coagulating gland can glycolyse anaero- 

 bically glucose at a much higher rate than fructose; this, in 

 turn, may be due to the ability of the tissue to re-phosphorylate 

 more effectively glucose to 6-phosphoglucose, than fructose to 



