58 The Biochemistry of Semen 



spermicidal substances, including organo-metallic compounds, there 

 are indications that it is due to the blockage of vital sulphydryl 

 groups in the spermatozoa. Thus for example, the immobilizing effect 

 of iodoacetate on bovine spermatozoa, which has been studied by 

 Lardy and Phillips (19436), is most probably due to the sulphydryl 

 group-binding capacity of this substance. In a war-time study 

 MacLeod (1946Z)) showed that the inhibition of the metabolism and 

 motility of human spermatozoa by organic arsenicals can be over- 

 come by 1:2: 3-trithiolpropane, and that the inhibitory effect of 

 cupric ions can be prevented by the addition of cysteine or gluta- 

 thione (MacLeod, 1951). Researches by Mann and Leone (1953) 

 have shown that both motility and fructolysis are abolished in 

 mammalian spermatozoa by several thiol reagents, including cupric 

 ions, hydrogen peroxide and o-iodobenzoate but that ergothioneine, a 

 normal constituent of boar seminal plasma, can efficiently counteract 

 the paralysing action of these reagents. The oxidation of sulphydryl 

 groups probably explains also the spermicidal action of hydro- 

 gen peroxide. The toxicity of hydrogen peroxide to spermatozoa, 

 noted already by Guenther (1907), is of particular interest since this 

 substance can actually be formed under certain conditions by the 

 spermatozoa themselves, in the course of their aerobic metabolism, 

 and is responsible for the so-called oxygen damage which occurs 

 as a result of oxygenation of semen (MacLeod, 1943^; Tosic and 

 Walton, 1946o, b; VanDemark, Salisbury and Bratton, 1949). Yet 

 another aspect of the damaging action of hydrogen peroxide has 

 been revealed by studies on the effect of X-rays on spermatozoa. 

 When sea-water heavily irradiated with X-rays was used as a diluent 

 for sea-urchin semen, there was a great reduction in the survival 

 period of spermatozoa and a considerable delay in the cleavage of 

 the eggs fertilized with these spermatozoa. The responsible toxic 

 agent present in the irradiated sea-water has been identified by 

 Evans (1947) as hydrogen peroxide. It is only fair to add, however, 

 that not all investigators agree with the conclusion that the toxicity 

 of irradiated media is due exclusively to hydrogen peroxide. 



Chemical aspects of short-wave radiation 



The chemical changes underlying the action of X-rays on sperma- 

 tozoa still remain largely unexplored, and the precise targets of this 



