28 FERTILIZATION 



Multivalent and univalent fertilizin. Tyler (1948) has put for- 

 ward the view that agglutination is caused by the combination of 

 fertilizin molecules which, like antigens and antibodies, are 'multi- 

 valent' * with respect to their combining groups, with spermatozoa 

 which are multivalent with respect to the number of receptor 

 groups on their surfaces. If, therefore, a fertilizin molecule is to 

 cause sperm agglutination, it must have at least two combining 

 groups so that two spermatozoa can become attached to it. If one 

 spermatozoon with two or more receptors on its surface combines 

 with two or more fertilizin molecules and each multivalent fertilizin 

 molecule combines with a number of spermatozoa, the observed 

 macroscopic agglutination will occur. Once spermatozoa have 

 reversibly agglutinated, they cannot be re-agglutinated and their 

 fertilizing capacity is reduced, Tyler (19410) has suggested that 

 the reversal of agglutination may be due to the fertiHzin molecules 

 being split into 'univalent' fragments by an enzyme in the sperma- 

 tozoa, or possibly by the movements of the spermatozoa themselves. 

 If the former hypothesis is correct, each spermatozoon will be 

 covered by univalent fragments and therefore cannot be re- 

 agglutinated by fresh fertilizin. In spite of certain obvious differ- 

 ences, the agglutination of vertebrate blood cells by influenza and 

 other viruses is a rather similar phenomenon as the reaction is 

 spontaneously reversible, after which the blood cells cannot be 

 re-agglutinated (Hirst, 1942). This haemagglutination reaction is 

 inhibited by a number of cell-free extracts and tissue fluids and 

 there is some evidence that the reactive groups of the inhibitors 

 and the blood cells are mucopolysaccharides. The receptor groups 

 are sensitive to periodate, as is fertilizin (Vasseur, 1952). In sup- 

 port of the multivalent fertilizin theory, Tyler (1941a, i942«) 

 showed that treatment of fertilizin with proteolytic enzymes, ultra- 

 violet light and heat made it incapable of causing sperm agglutina- 

 tion, though spermatozoa treated with this modified fertilizin could 

 not be agglutinated by normal fertilizin and sustained a loss of 

 fertilizing capacity without impairment of motility. (Untreated 

 fertilizin also reduces the fertilizing capacity of homologous 

 spermatozoa.) Tyler suggested that the above treatments of fer- 

 tilizin converted it into a univalent form. The spermatozoa com- 



* The Lattice theory of antigen-antibody combination requires the existence 

 of divalent or multivalent antibodies ; but the existence of such antibodies has not 

 yet been unequivocally demonstrated. 



