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Discussion 



Siekevitz: In your autoradiographs did you see any protein which would be 

 labelled in the supernatant without first being labelled in the microsomes ? 



Perlmann: We know that some of the typical "liver" antigens in the cell sap 

 will become labelled after a long period of incubation but we have not been able 

 to identify them since there are so many antigens in this fraction. We only know 

 that these labelled antigens are immunologically different from the serum proteins. 

 So far, we cannot exclude their presence in the microsomal extract. 



Marshall : I wonder if you or anyone you know of has tried labelling similar 

 antigenic systems with an isotope which goes not into the proteins but into phos- 

 pholipids for example ? Also I should like to ask whether you have any indication 

 that lipid rather than protein constituents are responsible for antigenic specificity 

 in any of these cases ? 



Perlmann: I don't think these methods have been used for the study of in- 

 corporation into the phospholipids or of the immunological properties of the lipid 

 fractions. Up to now, we have only used '*C amino acids and have followed their 

 incorporation into the proteins. 



