SPERM-EGG INTERACTING SUBSTANCES, I 25 



1949). These acidic properties are due to the large amount of acid- 

 labile sulphate, which may amount to 25% or more, in the mole- 

 cule. Fertilizin's sedimentation constant is 2-9-6-3 X lO"^^. 

 Measurements of diffusion coefficients are difficult to make on 

 fertilizin solutions, because they gelate at relatively low concen- 

 trations ; but on the basis of a sedimentation constant of 6-3 X io~^^ 

 and the value 2-i X lO"^ cm^/sec, which Tyler (1949) and Tyler 

 et al. (1954) considered the most accurate of their estimates of the 

 diffusion coefficient, the molecular weight of fertilizin from 

 Arbacia pmictulata is about 300,000. A reciprocal density of 0-65, 



TABLE 2 

 Preparation of powdered fertilizin from sea-urchin egg water 



(i) Prepare 20% suspension, by volume, of unfertilized eggs. 



(2) Bring pH to 3-5 with o-i N-HCl. 



(3) Centrifuge and remove supernatant. 



(4) Add 40 ml. N-NaOH per litre of supernatant. 



(5) Suspend precipitate in 3-3% NaCl and dialyze against 3-3% NaCl. 



(6) Remove insoluble particles and precipitate with ij vols. 95% ethanol. 



(7) Dissolve in 3*3% NaCl, re-precipitate with ethanol or saturated 



(NHJaSOj, and dry. 



Yield, ca. 250 mg./L. {S. purpuratus) 



which is of the right order for a polysaccharide, is assumed in the 

 calculations. The corresponding axial ratio (unhydrated prolate 

 ellipsoid) is 28: i, and, with a reasonable value for water of hydra- 

 tion, the ratio becomes about 20: i. 



Fertilizin with a high sulphur content, i.e. from egg suspensions 

 of Strongylocentrotus droebachiensis (O. F. Miiller) (9%), and Para- 

 centrotus lividus (8 %), gives a good agglutination reaction with homo- 

 logous spermatozoa. Egg jelly oi Brissopsis lyrifera (Forbes), which 

 has a small sulphur content, 2-7%, does not cause agglutination of 

 homologous spermatozoa, from which Vasseur (1952) concludes 

 that agglutination is dependent on fertilizin containing an adequate 

 number of sulphate groups. But we shall see, when considering 

 the serological aspects of agglutination, that non-agglutinating 

 fertilizin can be rendered agglutinating by the addition of adjuvants, 

 while agglutinating fertilizin can be rendered non-agglutinating by 

 various treatments, including trypsin (Tyler & Fox, 1940) and 

 periodate (Immers & Vasseur, 1949), which could be interpreted 

 as meaning that both the protein and the polysaccharide part of the 

 molecule are necessary for agglutination, though this is not 



