Abstract
1) Biosynthesis of folic acid was carried out by the culture of Lactobacillus arabinosus in the medium used for folic acid determination. In this case, pteroic acid, p-aminobenzoylglutamic acid, p-aminobenzoic acid, and pteridine-6-carboxylic acid, all assumed to be the intermediates of folic acid, were added to the medium but no effects were observed with the exception of PABA.
2) The amount of folic acid formed by L. arabinosus is not necessarily proportional to the degree of the bacterial growth.
3) Biosynthesis of folic acid is inhibited by the presence of sulfanilamides. Addition of the foregoing folic acid intermediates, in order to find the inhibition point, showed that the inhibition was the smallest when p-aminobenzoylglutamic acid was added, from which it was assumed that the sulfanilamides damaged the bonding of PABA and glutamic acid.
4) Inhibition of the growth of Lactobacillus arabinosus by sulfathiazole, when cultured in a synthetic medium used for the quantitative determination of folic acid, is antagonized by folic acid, p-aminobenzoylglutamic acid, and p-aminobenzoic acid, the strength being in that order. p-Aminobenzoylglutamic acid antagonizes sulfanilamides in 4-5 times the strength of PAPA.
5) Folic acid is the essential nutrient of Lactobacillus caseii and is not inhibited by sulfanilamides.
