Bisulfite Modification of Nucleic Acids and their Constituents

Xanthine oxidase/hydrogen peroxide generates sulfur trioxide anion radical (SO.−3) from sulfite (SO2−3)

“…This result has at least two significant implications: (i) it suggests a new property for xanthine oxidase; and (ii) it provides a possible new metabolic pathway for SO;-generation in cellular systems, where both H,O, and xanthine oxidase are present. As mentioned in the Introduction, it is generally believed that SO;-radicals play an important role in the biochemical mechanism of SO~-toxicity [2][3][4][5][6][7][8][9]. For example, SO;" radicals are known to cause many adverse reactions with biological molecules, including methionine and diphosphopyridine nucleotide oxidation [8,31], fl-carotene and tryptophan destruction [7,8], double bond addition in alkenes [32], fatty acid peroxidation [33], nucleic acid modification [3], and DNA cleavage [34].…”

“…Our current finding that the xanthine oxidase/H.,O, system can generate SO~-radical from SOl-suggests a new property of this enzyme. Second, this result points to a new enzymatic pathway for salfite metabolism and toxicity, since the SO;-radical has been implicated in the mechanism of toxic reactions resulting from sulfite exposure [2][3][4][5][6][7][8][9]. Third, we noted that while the mechanism of SO;-generation from SOl-via autoxidation and trace-metal catalyzed oxidation has been studied in detail [10][11][12][13][14], relatively little is known about the mechanism of SO;-generation through enzymatic pathway, with the exception of some recent studies [15][16][17][18][19].…”

The Synthesis of Deuterionucleosides

“…For uracil derivatives the reaction takes place only under basic conditions [64][65][66][67][68][69][70][71][72][73] .Sodium bisulfite…”

“…It adds across the 5,6-double bond producing stable 5,6-dihydro-6-sulfonate derivatives [67][68][69][70] . The mechanism of this process under basic conditions at elevated or at room temperature has been investigated in details 58,65,68,[70][71][72] and it is found that the bisulfite incorporation is dependent on the pH of the reaction medium, and the exchange is most efficient at pH 7-9 68,70 . Regeneration of uracil from the sulfonate adduct can be achieved by a treatment at pH >9 70 .…”

“…The mechanism of this process under basic conditions at elevated or at room temperature has been investigated in details 58,65,68,[70][71][72] and it is found that the bisulfite incorporation is dependent on the pH of the reaction medium, and the exchange is most efficient at pH 7-9 68,70 . Regeneration of uracil from the sulfonate adduct can be achieved by a treatment at pH >9 70 . It has been observed that ammonium sulfite could increase the rate of the exchange reaction 68 .…”