RNA-ASCORBATE INTERACTION

Ascorbic acid and divalent iron salts have been widely used to investi gate the effects of reactive oxygen species in different biological ta rgets such as nucleic acids, proteins and lipids. This study was desig ned to examine the interaction of yeast RNA with vitamin C in aqueous solution at physiological pH with drug/RNA(P)(P=phosphate) molar ratio s of r=1/80, 1/40, 1/20, 1/10, 1/4 and 1/2. Absorption spectra and Fou rier transform infrared (FTIR) difference spectroscopy were used to de termine the ascorbate binding mode, binding constant sequence selectiv ity and RNA secondary structure in aqueous solution. Spectroscopic evi dence showed that at low drug concentration (r=1/80 and 1/40), no majo r ascorbate-RNA interaction occurs, while at higher drug concentration s (r>1/40), a major drug-RNA complexation was observed through both G- C and A-U base pairs and the backbone phosphate groups with k=31.80 M- 1. Evidence for this comes from large perturbations of the G-C vibrati ons at 1698 and 1488 cm(-1) and the A-U bands at 1654 and 1608 cm(-1) as well as the phosphate antisymmetric stretch at 1244 cm(-1). At r>1/ 10, minor structural changes occur for the ribose-phosphate backbone g eometry with RNA remaining in the A family structure. The drug distrib utions around double helix were about 55% with G-C, 33% A-U and 12% wi th PO, groups. A comparison between ascorbate-RNA and ascorbate-DNA co mplexes showed minor differences. The ascorbate binding (If-bonding) i s via anion CO and OH groups.