Biosynthesis of Pyrimidines 163 



was diluted. That might indicate that orotic acid is a normal inter- 

 mediate. It has to be confirmed in other ways. We also tried carbon- 

 labelled aspartic acid (glutamic M^as not used) and carbon from this 

 also was incorporated into the pyrimidines. This of course doesn't 

 mean that aspartic acid is a precursor to orotic acid. We don't know 

 anything about that. At the moment we are trying pyruvic acid. 



Aterman: I would like to point out that the regenerating liver may 

 not be a normal organ. I have slides which show that within 5 minutes 

 after partial hepatectomy in the rat there is in the liver remnant a 

 type of vacuolation which is exactly identical with the vacuolation 

 described in hypoxic states, and I should think that functional changes 

 must occur as well. 



Neuberger: How are the samples to be counted prepared, and what 

 amount of material is counted? 



Wilson: They are obtained in solution, of course, from the columns. 

 The solution is evaporated down practically to dryness. Then single 

 drops of water are added to the little evaporating dish, the liquid is 

 taken off, placed on an aluminium planchet and evaporated again to 

 dryness. The great advantage of using the column over the paper alone 

 is that the solution is much cleaner when the column is used. If we 

 evaporate the solution from the paper, we have never been able to purify 

 the tertiary butyl alcohol enough so that there is no residue at all; 

 there is usually some residue from the alcohol and a little residue from 

 the filter paper. 



The amounts of pyrimidine nucleotides placed on the planchets were 

 from 100 to 1500 /ng., as indicated by the spectrophotometric absorptions. 



