CORRELATION BETWEEN MORPHOLOGICAL STRUCTURE 257 



that suggest strongly that the RNP particles attached to the endoplasmic 

 reticulum are the site of synthesis of the completed molecules of chymo- 

 trypsinogen and other hydrolytic enzymes of the pancreas. We have natur- 

 ally been interested to determine whether the same holds true for the rat 

 liver so far as albumin synthesis is concerned. 



Two aspects of this problem have occupied us. First we wanted to 

 know^ if the RXP particles contained any serum albumin. We have prepared 

 many batches of such particles after treating the microsome pellet with 

 DOC, extensive centrifugation at 105 000 g for 2^ hr., washing free of 

 DOC and further centrifugation. Such particles have the usual RNA/ 

 protein ratio of about 0-4. We have treated the particles with a variety of 

 agents and compared the amounts of soluble albumin in the supernatants 

 with that obtained by suspension in water. We have incubated the particles 

 in each of the following: pyrophosphate (5 x lO"^ u), ATP (5 x iq-* m), 

 NaCl (0-5 m), ethylenediaminetetra-acetic acid (2^0). ribonuclease (o • 5 

 mg./ml.) and, finally, 70% aq, acetic acid. None of these reagents had any 

 detectable effect on the immunological properties of serum albumin. We 

 have not obtained a consistent release of serum albumin from the particles 

 by any of these treatments. With ribonuclease the RNA/protein ratio was 

 reduced to about o-i, which may be taken to indicate a considerable 

 degree of disruption of the particle. So far, therefore, we have no evidence 

 of the presence of serum albumin in the RNP particles. 



The other aspect of our work has been an attemipt to obtain a synthesis 

 of serum albumin wdth the isolated RNP particles. We have studied the 

 conditions for the incorporation of amino acids into the protein of such 

 preparations. Like others, we find that provided the deoxycholate is 

 removed from the particles it is possible to obtain preparations which are 

 consistently active. It is not necessary to go into details, for our results 

 are very similar to those already described by Dr. Hultin. As with our 

 experiments on the synthesis of serum albumin by the isolated microsome 

 system, our initial aim w^as to demonstrate the incorporation of amino 

 acid into the purified serum albumin. The difficulty with the RNP particles 

 is that the cell sap is required for optimum activity and this contains large 

 amounts of serum albumin. Unlike the microsome preparation the particles 

 w^ould not be expected to retain the newly synthesized albumin so that the 

 latter would be diluted with the inactive albumin already present in the 

 cell sap. We have in fact failed to demonstrate an energy-dependent 

 incorporation of amino acid into the serum albumin on incubation of the 

 particles. 



To summarize therefore we have no evidence that the RNP particles 

 of rat liver are the site for the synthesis of the complete albumin molecule. 

 At present the results are consistent with the idea that in the liver the 

 initial incorporation of amino acids is into the RNP particles and that an 



