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We hereby explore the effects of irradiating DNA polyanions stored in a quadrupole ion trap mass spectrometer with an optical parametric oscillator laser between 250 and 285 nm. We studied DNA 6-20-mer single strands and 12-base pair double strands. In all cases, laser irradiation causes electron detachment from the multiply charged DNA anions. Electron photodetachment efficiency directly depends on the number of guanines in the strand, and maximum efficiency is observed between 260 and 275 nm. Subsequent collision-induced dissociation (CID) of the radical anions produced by electron photodetachment results in extensive fragmentation. In addition to neutral losses, a large number of fragments from the w, d, a *, and z *. ion series are obtained, contrasting with the w and (a-base) ion series observed in regular CID. The major advantage of this technique, coined electron photodetachment dissociation (EPD) is the absence of internal fragments, combined with good sequence coverage. EPD is therefore a highly promising approach for de novo sequencing of oligonucleotides. EPD of nucleic acids is also expected to give specific radical-induced strand cleavages, with conservation of other fragile bonds, including noncovalent bonds. In effect, preliminary results on a DNA hairpin and on double strands suggest that EPD could also be used to probe intra- and intermolecular interactions in nucleic acids.

The application of molecular beam deflection time-of-flight mass spectrometry (MBD-TOFMS) to peptide identification is described. The technique permits a simultaneous measurement of molecular mass and electric dipole susceptibility. The mass and susceptibility are not strongly correlated, and the results can be presented as a two-dimensional map. The susceptibility provides a useful way to disperse isobaric and isomeric peptides, and at least for small peptides, the susceptibility is significantly different for different amino acid sequences. Results for peptides in the mass range 1000-2300 Da show that the mass and susceptibility lead to a higher identification score than mass spectra alone.

The DC electric susceptibilities of unsolvated glycine-based peptides, WG(sub n), where n=1-5 is estimated by deflection of a molecular beam in an electric field. The results suggested that the peptides do not have rigid conformations with fixed dipoles but the peptides explore their energy landscape as dipole is averaged.

Temperature-dependent electric deflection measurements are performed for a series of unsolvated alanine-based peptides, Ac-WA(sub n)-NH2 and the measurements are interpreted using Monte Carlo simulations performed with a parallel tempering algorithm. The results suggest that unsolvated Ac-WA(sub n)-NH2 peptides with n greater than 10 adopt beta-sheet conformations at room temperature.

Studies of Zwittterion formation in small neutral alanine-based peptide using a direct probe of the charge distribution are reported. Molecular beam electric deflection measurements are used to determine the electric dipole susceptibility of insolvated WA(sub n) and Ac-WA(sub n)-NH(sub 2) peptides with up to five alanines.

Electron detachment was used to report the first electronic excitation spectra of polypeptides and of a protein in vacuo and demonstrated the feasibility of UV spectroscopy on large isolated biomolecular ions. Experiments provide a clear signature of the ionization of the tyrosyl group and electron detachment from a tyrosylate leads to the formation of a tyrosylate radical.

Research describing the conformation and the electric dipole of the unsolvated tryptophan is presented. Particular attention is given to the process of coupling a desorption source assisted by a matrix and a deflection of an electric beam.

Effects of various intakes of the ketoanalogues of leucine (KICA) and valine (KIVA) on growth, nitrogen, and urea excretion were examined and compared to those of an optimal intake (A) of the corresponding amino acids. Diet KICA and KIVA contents varied from 1 to 4 times A. In controls, growth was significantly reduced with equimolar substitution, corrected with twice A, and unchanged at higher levels. Doubling KICA corrected growth except with substantial anorexia. In uremic rats fed KIVA, growth was corrected at twice A. Low-KICA diets reduced plasma-leucine level; higher KICA diets normalized plasmaleucine and revealed branched-chain amino acid (BCAA) antagonism. Changes in 2-ketoacids were unrelated to those of BCAA. In uremia, KICA decreased plasma and urinary urea without changing nitrogen retention. Ketoacid substitution for amino acids was 50% efficient in normal rats and not altered by uremia. BCKAs, specifically KICA, could modify urea metabolism. [ABSTRACT FROM AUTHOR]