Fructose and Fructolysis 151 



6-phosphofructose. Such evidence as is at present available, derived 

 from both in vivo and /// vitro experiments, indicates that the 

 enzymic reactions involved in the conversion of blood glucose to 

 seminal fructose are as follows. 



Blood glucose 



\ 

 Glycogen 



^ Phosphorylase 



1-Phosphoglucose 



\ Phosphoglucomutase Phosphohexose 



6-Phosphoglucose \ >'6-Phosphofructose 



f \ 



Glucokinase Alkaline phosphatase 



isomerase 



Alkaline 

 phosphatase 



Glucose ^^ Seminal fructose 



Anaerobic and aerobic utilization of carbohydrate by spermatozoa 



The spermatozoa of the sea-urchin and certain other animals 

 derive their energy for movement chiefly from respiratory processes; 

 in contrast, the survival and motility of sperm ejaculated by animals 

 with internal fertilization, such as mammals, is possible for most 

 of them also in absence of oxygen, provided that the sperm cells 

 remain in contact with seminal plasma. Mammalian spermatozoa 

 possess only a negligible reserve of intracellular glycogen and depend 

 therefore, under anaerobic conditions, on an extracellular source of 

 energy. In species which contain fructose as a normal constituent 

 of the seminal plasma, anaerobic fructolysis is the metabolic process 

 which enables the spermatozoa to survive without oxygen. Should, 

 however, the spermatozoa become separated from the seminal 

 plasma by centrifugation and washing, they could not carry on 

 anaerobically unless the seminal plasma were restored or replaced 

 by glycolysable carbohydrate. 



The stimulating effect of pure sugars on sperm motility has been 

 noticed by some of the early investigators of semen. In 1931 Ivanov 

 observed that dog spermatozoa suspended in an isotonic solution of 

 glucose and phosphate retained their motility when the respiration 

 had been abolished either by poisoning with cyanide or by replace- 

 ment of oxygen with hydrogen. This observation is of particular 

 interest in view of the fact that the dog has no seminal vesicles and 



