AN ISOANTIGENIC LIPOPROTEIN 8l 



sites, of the lipoprotein, we have begun to investigate ways in 

 which the structure of TSL can be modified, and the effects of 

 structural modifications on activity as measured by the enhance- 

 ment and haemagglutination inhibition tests. Structural modi- 

 fications that increase the solubility in water of the lipoprotein 

 can be determined conveniently by measuring changes in the 

 turbidity of a suspension of the lipoprotein. TSL, suspended by 

 homogenization in o*iM-tris buffer, pH 7-9, at a concentration 

 of o-i mg./ml., gives a turbidity reading of 0-15 (measured as 

 absorbancy at 660 m[jL in a i cm. cell in a Beckman DB spectro- 

 photometer). The effects of some enzymes on the turbidity of 

 such a suspension are shown in Fig. 5. The addition of trypsin or 

 chymotrypsin to the suspension produced a rapid but limited 

 decrease in turbidity. Addition of lipase produced a relatively 

 slow decrease in turbidity which also approached a limiting value 

 while considerable turbidity was still evident. Turbidity decreased 

 rapidly in the presence of snake venom and the reaction proceeded 

 to the point where the suspension appeared optically clear after 

 approximately one hour. Boiled venom was inactive, suggesting 

 that the active factor may be an enzyme. Pepsin had no effect on 

 turbidity under the conditions used. 



In view of the marked solubilizing effect of snake venom it is of 

 interest to examine further the immunological and chemical 

 properties of the altered TSL. Because of the limited amount of 

 TSL available only the preliminary studies described below have 

 been carried out to date. 



One hundred mg. of TSL in three ml. of o- iM-tris buffer pH 

 7*9 was digested with 2*8 mg. of snake venom for one hour at 

 room temperature (22°). The mixture was then dialysed for five 

 hours with stirring i^crsus o- iM-acetate buffer pH 5. The resulting 

 precipitate, centrifuged down, washed twice with buffer and 

 freeze dried, weighed 78 mg. It dissolved in o-iM-tris or bar- 

 bitone buffers (pH 7-9 and 8 • 6, respectively) to give a tan, shghtly 

 opalescent solution. Moving boundary electrophoresis indicated 



