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Vitamin Para-Aminobenzoic Acid (PABA) Controls Generation of Nitric Oxide (NO) In Vitro and its Biological Functions in the Bacterial Cells

Svetlana V Vasilieva1*, Maria S Petrishcheva1, Elizaveta I Gusarova1 and Andreyan N Osipov2,3

Nitric oxide (NO) serves either a universal signaling molecule or extremely toxic agent, depending on the dose. Up to date there have been a very limited number of natural compounds serving as effective regulators of NO signaling and toxic potencies. NO acts in concert with H2S to coordinate cell responses; however, how exactly this interaction is achieved is not known. Both agents have an effect on the accumulation of both reactive chemical species, ROS and RNS and can give rise to other reactive species. Para-aminobenzoic acid (PABA) is an essential metabolite for certain organisms. Once considered a vitamin, PABA, functions as an effective inhibitor of inducible SOS DNA repair processes in E. coli. In the present study we focus on the genetic and physiological evidence in favor of interference of NO-donors and PABA in bacterial cells with DNA repair gene expression and biofilm formation, depending on the rate of NOdonating in vitro and intracellular ROS/RNS accumulation in the cells. The crystalline dinitrosyl iron complexes (NO- 29 and NO-33) with thiourea as the ligands and 3 crystalline tetranitrosyl iron complexes with thiosulfate (TNICthio) - and with sulfur-containing aliphatic ligands – cysteamine and penicillamine were studied first as the NO-donors in pure solutions and in the combination with PABA. In E. coli cells with the combined action of PABA (0.01-5 mM) with nitric oxide donors we observed an inhibition of NO-signaling potency in the SOS (sfiA gene)- and the SoxRS (soxS gene) DNA repair pathway up to 3.5 fold, depending on the dose of PABA. PABA tested at 0.5 mM afforded 24% protection against the level of biofilm formation induced by TNICthio. Using the antioxidant-capacity assay, we observed a many-fold decrease in the ROS/RNS level production in the samples of E. coli cells with PABA and NO-donor-TNICthio.