Ultraviolet-Driven Deamination of Cytidine Ribonucleotides Under Planetary Conditions.

A previously proposed synthesis of pyrimidine ribonucleotides makes use of ultraviolet (UV) light to convert ß-d-ribocytidine-2',3'-cyclic phosphate to ß-d-ribouridine-2',3'-cyclic phosphate, while simultaneously selectively degrading synthetic byproducts. Past studies of the photochemical reactions of pyrimidines have employed mercury arc lamps, characterized by narrowband emission centered at 254 nm, which is not representative of the UV environment of the early Earth. To further assess this process under more realistic circumstances, we investigated the wavelength dependence of the UV-driven conversion of ß-d-ribocytidine-2',3'-cyclic phosphate to ß-d-ribouridine-2',3'-cyclic phosphate. We used constraints provided by planetary environments to assess the implications for pyrimidine nucleotides on the early Earth. We found that the wavelengths of light (255-285 nm) that most efficiently drive the deamination of ß-d-ribocytidine-2',3'-cyclic phosphate to ß-d-ribouridine-2',3'-cyclic phosphate are accessible on planetary surfaces such as those of the Hadean-Archaean Earth for CO2-N2-dominated atmospheres. However, continued irradiation could eventually lead to low levels of ribocytidine in a low-temperature, highly irradiated environment, if production rates are slow.

Photoinduced interaction of Ru(bpy)3 2+ with nucleotides and nucleic acids in the presence of S2O8 2-; a transient conductivity study.

The photochemical reactions of Ru(bpy)3(2+) with single- and double-stranded DNA, polynucleotides and purine-containing nucleotides in argon-saturated aqueous solution in the presence of S2O8(2-) were studied using time-resolved absorption and conductivity methods. The conversion of Ru(bpy(3(3+) to Ru(bpy)3(2+), monitored spectroscopically either after rapid mixing with substrate or after laser flash excitation (lambda exc = 353 nm) is quantitative at nucleotide-to-sensitizer ratios [N]/[S] of 1-2 for DNA and other guanine-containing compounds. Conductivity measurements following the laser pulse revealed a fast conductivity increase (rise time, less than 0.1 ms) due to the formation of protons and, to a lesser degree, to charged species of much lower ion mobility. A slower component in the 0.01-1 s range was observed for nucleic acids; its amplitude is markedly reduced at pH 6-9. In buffered neutral solution the signal is replaced by a slight decrease in conductivity. Electronically excited Ru(bpy)3(2+) bound to DNA reacts with S2O8(2-) to form Ru(bpy)3(3+) and SO4(.-) as primary oxidizing species both of which react with bases. The resulting base radicals react subsequently with Ru(bpy)3(3+) and Ru(bpy)3(2+) or the ligands in the ruthenium complex, producing protons which give rise to the slower conductivity increase. The formation of single-strand breaks and the ensuing release of condensed counterions does not appear to contribute significantly to the slow component. The transient conductivity behaviour is sensitive to the single- or double-stranded nature of DNA.

Identification and characterization of radiation damaged products of monophosphate nucleosides by on-line capillary isotachophoresis-electrospray ionization mass spectrometry.

Analysis of trace levels of DNA damage as a biomarker of human exposure to radiation levels represents a significant challenge. Capillary isotachophoresis (CITP) is well suited for this application due to its high separation efficiency, large sample loading capacity, and relative ease of interfacing with highly specific and sensitive mass spectrometric detectors. This study describes the use of reversed anionic CITP coupled on-line with electrospray ionization-mass spectrometry (ESI-MS) for the identification and characterization of small quantities of radiation induced damage to deoxynucleotide monophosphates. CITP with ESI-tandem MS also provides structural information on the nature of the damage in addition to the molecular weight. This approach has the attraction of allowing the direct on-line determination of damaged nucleotides, as well as the free bases and nucleosides, and avoids the need for sample hydrolysis and/or derivatization.

Some parallelisms n the behavior of pancreatic ribonuclease and chicken lysozyme toward homopolyribonucleotides.

Pancreatic ribonuclease and chicken lysozyme possess gross similarities that are responsible for a common ability to form enormous light-scattering centers in cooperation with homopolyribonucleotides. The light-scattering power of the mixtures is highest when [homopolymer]/[protein] assumes some critical value that is unique for each homopolymer-protein pair. In some respects the scatterers resemble very large antigen-antibody networks. A criterion is established to ascertain the relative abilities of the homopolymers to form the centers with the two proteins. Both see polyinosinic acid (poly-I) as most and polyadenylic acid (poly-A) as least efficient in this respect.