CYTOPLASMIC AND NUCLEAR STRUCTURE IN 

 RELATION TO METABOLIC ACTIVITIES 



J. Brachet 



University of Brussels 



Among the numerous theories which have been proposed 

 with a view to explaining the functions of the nucleus in the 

 life of the cell, several have now been definitely rejected. This 

 is true in particular for the hypothesis of Loeb (1899) who 

 considered the nucleus as the prime centre of cellular oxida- 

 tions, for we have now shown, both for amoebae and for the 

 unicellular alga Acetahularia mediterranean that removal of 

 the nucleus does not appreciably reduce the rate of cellular 

 oxidations, even after a considerable length of time (Brachet, 

 1955a). It is also now well known that isolated nuclei have 

 an extremely low oxygen consumption and lack most of the 

 oxidative enzymes, this being true for amphibian egg nuclei 

 obtained by microdissection (Brachet, 1939) and for nuclei 

 of liver homogenates prepared by differential centrifugation 

 (cf. recent review articles by Bounce, 1955; Allfrey, Daly and 

 Mirsky, 1955). Extensive research on liver homogenates has 

 shown, in addition, that mitochondria are the primary, 

 though not exclusive, site of the energy-generating reactions 

 of the cell (oxidative phosphorylations). This work has been 

 ably summarized in recent reviews by de Duve and his co- 

 workers (de Duve and Berthet, 1954) and by Hogeboom and 

 Schneider (1955). An interesting exception, as yet uncon- 

 firmed, has been reported by Rubinstein and Denstedt (1954): 

 bird erythrocytes lack mitochondria and contain oxidative 

 enzymes (cytochrome oxidase and succinic dehydrogenase) in 

 their nuclei. 



The fact remains, however, that the metabolism of enucle- 

 ated cytoplasm is never entirely normal. In the case of 



3 



