The physiological significance of p-Aminobenzoic Acid

Bloomberg, B. M.
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The interest of the biochemist in para-aminobenzoic acid is very recent and, indeed, only goes back about five years, but in this time quite a voluminous literature has accumulated on the biological aspects and importance of this aniline derivative. Attention was originally focussed on it indirectly as a result of the intensive research devoted to the understanding of the mode of action of the various sulphonamides, which were shown during the last decade to be very powerful chemothera-peutic agents against many bacteria. Fildes (1940, propounded the hypothesis that p-aminobenzoic acid was an essential meta-bolite for bacteria, that it was normally associated with an enzyme system in the bacterial cell, and that sulphanilamide, being structurally similar to p-aminobenzoic acid, was capable in sufficient concentration of displacing p-aminobenzoic acid from its enzyme and stopping this essential line of metabolism. Fildes further suggested that a substance which was found to be an essential metabolite for bacteria would also be essential in the animal kingdom, so that such a substance might be found to act as a vitamin in the higher animals and even in man. In 19U1 interest in p-aminobenzoic acid was intensified with the announcement by Ansbacher (19U1J that p-eminobenzoic acid was actually a vitamin and should be included in the vita¬min B complex. In this thesis, studies on the absorption and excretion of p-aminobenzoic acid are reported, the estimation of p-amino- bensoic acid being based on its property of antagonising the Bulphonamides. Evidence is presented that p-arainobenzoic acid la excreted ae p-acetylaminobenzoic acid, and that its conjuga- tion with the acetyl radical probably takeB place in the liver. Further it is suggested that the experiments performed do not lend support to the view that p-aminobenzolc acid is a vitamin for man. Finally the various physiological effects of p-aminobenzoic acid are discussed and an attempt is made to gauge its function in the living organism. Preliminary experiments indicating a new, hitherto unreported, role of p-aminobenzoic acid are re¬corded, namely its ability in large doses to increase the re¬sistance of animals to disease.
Thesis submitted for the Degree of Doctor of Medicine in the University of the Witwatersrand, Johannesburg