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

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.