Biochemistry:Biosynthesis of p-aminobenzoic acid
The acid p-amino benzoic acid or pABA is not synthesized in vertebrates; enzymes and, consequently, the pathways are only present in prokaryotes and in plant cells. The three precursors of p-amino benzoic acid, in order of distance from the pathway are the eritrosio, chorismate and pyruvate.
The pentose phosphate pathway leads to the formation of eritrosio-4-phosphate, a sugar aldotetrose who, along with phosphoenolpyruvate from glycolysis, goes to the metabolic pathway of the shikimate. The chorismate is the end product of the shikimate pathway and is the essential precursor for the biogenesis of p-amino benzoic acid (4); generally speaking the shikimate pathway is a pathway for the synthesis of a large number of compounds, particularly aromatic with biological functions, such as important antioxidants (5).
In E. coli, p-amino benzoic acid is synthesized in a series of two enzymatically catalyzed reactions (6) starting from chorismate and L-glutamine. The enzymes involved are called pabA, pabB and pabC (Figure 3).
Figure 3 the formation of p-amino benzoic acid by chorismate
In plants, p-amino benzoic acid is synthesized in the chloroplast, and transported in mitochondria where it is used for folate biosynthesis. Most of the acid is, however, present in glycosylated (glu-pABA) form at the level of the vacuole, where is preserved (Figure 4).