Microbial Mutants SI 



visionally consider a side product, simply on the basis of the 

 fact that among our 59 mutants blocked somewhere from 

 before DHQ to after compound Zl, not one has been 

 blocked between shikimic acid and phosphoshikimic acid. 



With respect to quinic acid, I have even more serious 

 reservations, despite its growth-factor activity for an Aero- 

 hacter mutant (12) and also for a Neurospora mutant (15). 

 These reservations were originally based on two facts: (a) 

 we could not obtain an Aerobacter auxotroph blocked be- 

 tween quinic acid and DHQ, and (b) the E. colt mutants 

 that responded to DHQ neither responded to nor accumu- 

 lated quinic acid; and if these strains had been blocked be- 

 tween the two compounds, they would have been expected 

 to accumulate quinic acid. The case against this compound 

 is now very much strengthened by the fact that quinic de- 

 hydrogenase, though present in Aerobacter, is absent from 

 many other species, including E. coli, that do possess other 

 enzymes of this path. Since Aerobacter has the same path 

 as these other organisms beyond DHQ, it very likely also 

 has the same path leading up to DHQ. Its enzyme for con- 

 verting quinic acid to DHQ would then have to be regarded 

 as an adventitious one, not essential for aromatic biosyn- 

 thesis from glucose. This problem can be definitively 

 settled when the enzymatic step before DHQ is worked 

 out in Aerobacter and E. coli. 



I should like to say a few words on the subject of growth- 

 factor activity. Although this property has directed us to 

 some of the compounds under investigation, we now 

 blithely disregard it in assigning to each compound its 

 place either at the table or in the corner. We accept pre- 

 phenic acid, though it has no activity; we reject quinic acid, 

 though it has activity. How can we account for the inactivity 

 of a true intermediate? 



One example is based on the fact that all mutants blocked 

 immediately before shikimic acid show little response to 

 this compound. The reason is that these strains accumulate 



