46 The Biochemistry of Semen 



of spermatozoa in the semen and the degree of sperm motility 

 (Mann, 1949). The more chemical aspects of semen metabolism 

 will be discussed fully in conjunction with specific groups of sub- 

 stances metabolized by spermatozoa, such as sugars, lipids and 

 amino acids. Here, only the general outline of sperm metabolism 

 will be given, in so far as it helps to bring out the relationship 

 between the metabolic processes and other characteristics of semen, 

 in particular, sperm concentration and motility. 



Glycolysis 



In the absence of oxygen, for example under the conditions of 

 semen storage for artificial insemination, the spermatozoa rely on 

 carbohydrate metabolism as the chief source of energy. Even before 

 the identity of the seminal sugar was revealed, the rate of lactic acid 

 production or 'glycolysis' was used as a method for semen appraisal 

 (Comstock, 1939; Webster, 1939; MacLeod, 1941a, b, 1943Z); Moore 

 and Mayer, 1941; Comstock, Green, Winters and Nordskog, 1943; 

 Laing, 1945; Salisbury, 1946; Westgren, 1946.) However, the dis- 

 covery of fructose and the work on fructolysis made available a 

 chemical approach to several practical problems of male fertility 

 (Mann, 19466, 1948«, b, 1949; Mann, Davies and Humphrey, 1949; 

 Mann and Lutwak-Mann, \95\a, b; Mann and Parsons, 1950; 

 Mann and Walton, 1953). 



The anaerobic incubation of freshly ejaculated semen is accom- 

 panied by a progressive decline in the content of fructose with a 

 simultaneous accumulation of lactic acid; in the presence of suitable 

 buffer, the process of fructolysis in semen with good sperm motility 

 can be shown to progress almost linearly until practically all of the 

 sugar is used up (Fig. 8). On this basis a photometric method has 

 been worked out for the measurement of sperm fructolysis, and the 

 'index of fructolysis' has been defined as the amount of fructose (in 

 mg.) utilized by 10^ spermatozoa in 1 hr. at 37° (Mann, 1948^, b). 

 In normal bull semen, the index of fructolysis is about 1 -4-2 but it 

 varies, and is significantly correlated with both the concentration 

 and the motility of spermatozoa. Fructose is not utilized by either 

 azoospermic semen, i.e. ejaculates devoid of sperm, or by necro- 

 spermic semen, containing immotile spermatozoa. The existence 

 of a positive correlation between the rate of fructolysis and the 



