ON THE MEANING OF INTRACELLULAR 

 STRUCTURE FOR METABOLIC REGULATION 



Philip Siekevitz 



Rockefeller Institute for Medical Research, New York City 



This presentation deals with some of the facts of the existing 

 cytological findings on cell structure and with the biochemical 

 inferences which may be deduced from them. As such, it will 

 abide within the spirit of this symposium, which has to do not 

 with the recitation of the old, nor even of the new, but with 

 the contemplation of the foreseeable. 



By now, I hardly dare suggest that the cell is not a bag, but 

 I do think that most biochemists do not fully realize to what 

 extent the cell is made up of more or less distinct compart- 

 ments. Due mostly to the pioneering work of Porter and 

 Palade in America and Sjostrand and his group in Sweden (cf. 

 Sjostrand, 1956), we know that the cytoplasm is divided into 

 numerous compartments, which include the nucleus, the 

 mitochondria, various inclusion bodies in different cells, and 

 the endoplasmic reticulum. Of these, the latter is least 

 understood, and therefore, considering the nature of this 

 symposium, will be the one discussed in the present paper. 

 This system, and some physiological implications which can 

 be deduced from its existence, have been described in a 

 recent excellent review by Palade (1956a). I propose to go on 

 from there, bringing in some biochemical concepts to fulfil the 

 intimations previously expressed. 



It is agreed among the majority of cytologists that the 

 endoplasmic reticulum (ER) is a system of lumina limited by 

 a membrane (about 75 a thick) and taking the forms of 

 canals, vesicles and lacunae or cisternae within the cell. 

 These spaces are more or less interconnected among them- 

 selves and form a continuum which permeates the cytoplasm 



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