THE INTERPHASE NUCLEUS 



from microcolorimetric measurements is higher than that derived by 

 the bulk analysis of isolated nuclei. These authors concluded that their 

 observations demonstrate that protein is lost from nuclei during their 

 isolation. The comparison rests, however, on the validity of the cy to- 

 chemical procedures which were used. Their figures for the DNA 

 nuclear content were calculated according to Di Stefano's method, 

 which has subsequently been found inadequate, notably by one of the 

 above authors herself (p 36). 



Some part of the non-basic proteins of the interphase must be 

 enzymic. In isolated nuclei a number of enzymes have been shown to 

 be present, although the possibility that some of their activity is due to 



ci^r::^ 



BuOH 

 AcOH 



Figure 1 6 Paper chromatogram of acid hydrolysate of the sap 

 of the oocyte nucleus of Xenopus laevis. (i) aspartic acid; 

 (2) glutamic acid; (3) glycine; (4) serine; (5) lysine; (6) 

 threonine; (7) alanine; (8) tyrosine; (9) arginine (histidine, 

 if present) ; (10) proline; (11) valine; (12) phenylalanine; 

 (13) leucine and isoleucine. The colour differentiation indi- 

 cated by letters in parenthesis (Bl, blue; V, violet; P, pink; 

 G, grey; Y, yellow) was produced by 5% collidine in the 

 ninhydrin spray. From Brown et alii^'^ {By courtesy. Nature). 



contamination by cytoplasmic material is always present; where, 

 however, enzymes are present in relatively high concentration in 

 isolated nuclei this source of error is less probable. Dounge^^^ found 

 that a number of enzymes were conspicuous in rat liver nuclei, and 

 that they were not removed by washing, as was the adsorbed haemo- 

 globin. Among them were both acid and alkaline phosphatases, which 

 have also been identified in isolated nuclei of the cerebral cortex by 

 RiCHTER and Hultin,^^* who found that the latter enzyme was more 

 abundant in the nucleus than in the cytoplasm.* 



* DouNCE^^* has reviewed the various methods which are used for the isolation of nuclei. 



49 



