212 E. Hammarsten 



2 ng. of guanine) plus 5 ^g. of diaminopurine, the additional purine 

 stimulates the gro\^'th; and if [i*C]-dianiinopurine is administered, it is 

 converted into both adenine and guanine in about the proportion that it 

 is present in the medium. If the diaminopurine is as high as 50 ^g. 

 per ml., which is an inhibitory level, you still get about half as much 

 grow-th. This still gives something to work up for the tracer experiment, 

 and even here diaminopurine is still very efficiently utilized for both 

 adenine and guanine synthesis. Recently Dr. Hitchings has been 

 doing some growth studies which we are now following up with tracer 

 studies. If you give the micro-organism an induction period w ith about 

 0-2 ixg. of adenine for a day, during which time there is very little 

 growi:h, then put in plenty of diaminopurine, the organism grows 

 perfectly well with diaminopurine as a precursor of both of the purines. 

 We are trying to find out how diaminopurine can behave both as a 

 metabolite and as an anti-metabolite, but as yet cannot find any great 

 difference in its metabolism when it is acting as a growth inhibitor. 



Unfortunately we don't have parallel studies on the metabolism of 

 the protein, but we'll leave that to you. 



