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Microsomal Structure and Hemoglobin 

 Synthesis in the Rabbit Reticulocyte 



HOWARD M. DINTZIS HENRY BORSOOK JEROME VINOGRAD 



Gates and Crellin Laboratories of Chemistry 



and Kercl^hoff Laboratories of Biology 



California Institute of Technology 



A great deal of evidence has now accumulated which suggests very strongly 

 that microsomal particles are somehow connected with the process of protein 

 synthesis [1, 2, 3]. Because of their high content of ribonucleic acid which 

 might act as a coding template, it has become fashionable to postulate that these 

 particles are the actual sites of protein assembly from activated single amino 

 acids. To date, however, no evidence has been put forth which could be called 

 direct proof that such is indeed the case. 



Nevertheless, the hypothesis is so attractive that it seems worth while to pro- 

 ceed on the assumption that it is true and to investigate the detailed structure 

 of microsomal particles and the relation of this structure to the protein which 

 the particles are supposedly synthesizing. Such a study would have as its object 

 an understanding of the molecular nature of the microsomal particle, the molec- 

 ular structure of the growing peptide chains of the protein being synthesized, 

 and, if possible, the interrelation between the two. 



To best carry out such a study, one would like to find a system consisting of 

 free floating cells of a single type, actively engaged in the synthesis of predomi- 

 nantly a single type of protein molecule. Fortunately these desirable properties 

 are exhibited by mammalian reticulocytes. Such cells can be made in quantity 

 if rabbits are made anemic by daily injections of phenylhydrazine. After a 

 week of such injections, reticulocytes (immature red cells) account for 80 to 90 

 per cent of the red cells present in the blood. These cells are actively producing 

 hemoglobin and will continue to do so for many hours if suspended in the 



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