The p -Aminobenzoic Acid Requirement of the “Sulfonamide-Requiring” Mutant Strain of Neurospora

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Abstract
By measuring the growth response of wild strains and those mutant strains of Neurospora requiring sulfonamide, PABA, and both sulfonamide and PABA, in the presence of pteroyl-triglutamic acid, pteroyl-glutamic acid, pteroic acid, p-aminobenzoylglutamic acid and p-aminobenzoic acid, the effect of folic acid compounds and sulfonamides on these strains of Neurospora was studied. Conclusions were as follows: Neurospora cannot use pteroyl-glutamic acid, pteroic acid or p-aminobenzoylglutamic acid to replace p-aminobenzoic acid. These folic acid compounds contain a certain amt. of free PABA, which explains a positive growth response of the p-aminobenzoicless mutant and the double mutant p-aminobenzoicless, sulfonamide-requiring. The double mutant can grow well on low cons. of PABA (10-8 to 10-7M), but is poisoned by greater concs. and requires SA (sulfanilamide) as a detoxicant. The sulfonamide-requiring strain must: produce more than the tolerated amt. of PABA and thus inhibit itself.
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