214 



PETER PERLMANN AND WINFIELD S. MORGAN 



study of isotope incorporation. This has been done in several of the cases 

 referred to above, as in the case of the serum albumin [4, 21, 22], or in the 

 case of the beta galactosidase in E. coU [8]. In the following, this will be 

 exemplified briefly with some experiments from this laboratory. A detailed 

 discussion of the results will be published elsewhere [10]. The purpose of 

 these experiments was to study, qualitatively and under various experi- 

 mental conditions, the pattern of in vitro incorporation of isotopes into the 

 bulk of immunologically distinct proteins of fractionated homogenates. 



Figure 2 shows the results of an experiment with rat liver slices, in- 

 cubated for 30 min. with ^^C amino acids. After incubation, the slices were 



cA \~y 



a-m 



a-a 



ib) 



Fig. 2. (rt) Photograph, and {b) autoradiograph, of precipitin reactions of 

 lubrol extracts of microsomes {LU) and of a cell sap {CS), from rat liver, with 

 various antisera {a-m : antiserum against liver microsomes ; a-cs : antiserum against 

 liver cell sap; a-a: antiserum against rat serum albumin). The antigen solutions 

 were obtained from a fractionated homogenate of liver slices, previously incubated 

 for 30 min. with ['*C]-L-leucine, -L-isoleucine, and -L-valine. The radioactivity 

 of the TCA-precipitated protein of an aliquot of the total homogenate was 425 

 c.p.m./mg. protein and of an aliquot of the isolated cell sap 311 c.p.m./mg. 

 protein. From Morgan et al. [10]. 



homogenized, and a lubrol extract of the microsomes and the cell sap was 

 reacted with antiserum on agar plates. After completion of the immuno- 

 logical reactions, the agar plate was dried and covered with an X-ray film 

 for 3 weeks (cf. also [16, 20]). 



Figure 2{a) is a photograph of the precipitin reactions. As can be seen, 

 the two antigen solutions were reacted with an anti-liver microsomal 

 serum, an anti-liver cell sap serum, and an antiserum against rat serum 

 albumin. Both anti-liver sera had been absorbed with rat serum and were 

 free of precipitating antibodies against serum proteins. The antiserum 

 against serum albumin contained antibodies against the albumin, and in 



