JMSSJ On-line Abstracts, Vol.50, No.2 (2002)

Reduction in Desorption Mass Spectrometry: Multiple Protonation on Flavins without Charge Increment

Yoshiyuki ITOH,^a) Yoko OHASHI,^*b) Toshimichi SHIBUE,^c) Akio HAYASHI,^{a), †} Shojiro MAKI,^a) Takashi HIRANO,^a) and Haruki NIWA^a) (^a) Dept. of Applied Physics and Chemistry, The Univ. Electro-Communications (1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan)^*b) Center for Instrumental Analysis, The Univ. of Electro-Communications (1-5-1 Chofugaoka, Chofu, Tokyo 182-8585, Japan) ^c) Materials Characterization Central Laboratory, Waseda Univ. (3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan)^† Present address: Graduate School of Materials Science, Advanced Institute of Science and Technology, Hokuriku (Tatsunokuchi, Nomi, Ishikawa 923-1292, Japan))

J. Mass Spectrom. Soc. Jpn., 50(2),52-57, 2002

Three flavin-containing compounds, namely, riboflavin, riboflavin 5'-phosphate (flavin mononucleotide, FMN) and flavin-adenine dinucleotide (FAD, Scheme 1), were studied using matrix-assisted laser desorption ionization (MALDI), fast atom bombardment (FAB) and electrospray ionization (ESI) mass spectrometry. It was found that the isoalloxazine ring (flavin) was reduced in the positive-ion MALDI and FAB ionization processes producing unusual ions [M+2]^+· and [M+3]⁺ in addition to the anticipated [M+1]⁺, whereas ESI generated only [M+H]⁺ as the molecular-related ion. The reduction mechanism is hypothesized as the protonation from the matrix with a concomitant electron transfer,^*1 rather than the transfer of hydrogen atom(s), H^·_·ESI, in which matrix is not used, did not produce [M+2]^+· nor [M+3]⁺ more than the natural isotope abundance of ¹³C in the sample molecules. The reduction site expands to N(1)=C(10a)-C(4a)=N(5), a1,4-diaza-1,3-butadiene system, in the isoalloxazine ring, resembling the behavior of prosthetic groups of aerobic dehydrogenases.

Structure Elucidation of Hexasaccharide Derivatives Obtained from Keratan Sulfates by Ion Trap Mass Spectrometry

Masayuki KUBOTA,^*a) Keiichi YOSHIDA,^b) Akira TAWADA,^b) and Mamoru OHASHI^c) (^*a) Application Lab., ThermoQuest K.K. (Nishi-Shinjuku Toyokuni Bldg., 2-5-8 Hatsudai, Shibuya-ku, Tokyo 151-0061, Japan) ^b) Tokyo Research Institute, Seikagaku Corporation (Higashiyamato-shi, Tokyo 207-0021, Japan)^c) Department of Chemistry, Kanagawa University (Tsuchiya, Hiratsuka, Kanagawa 259-1293, Japan))

J. Mass Spectrom. Soc. Jpn., 50(2),58-66, 2002

Positive and negative ion electrospray ionization coupled with an ion trap mass spectrometer has been applied to the structure elucidation of three unknown species of hexaglycosides of lactosamine series obtained from keratan sulfates. Using positive and negative ion ESI-MS, the molecular weights of three unknown compounds were determined to be 1,127 (3L1P1), 1,141 (3L1P2), and 1,159 (3L1P3) corresponding to M+14, M+28, and M+46 respectively where M represents the molecular weight of the unmodified lactosamine trimer (3L1); Galβ1→4GlcNAcβ1→3Galβ1→4GlcNAcβ1→3Galβ1→4GlcNAc, M=1,113. Among them the structure elucidation of compound 3L1P1 and 3L1P3 is discussed in this paper in detail. The positive and negative (MS)⁴ of the disaccharide fragment ions (m/z 420 and 396, respectively) of 3L1P1 overlaps with the positive and negative (MS)² spectra of known N-acetyllactosamine methyl glycoside (L1-OMe), respectively. On the basis of this finding the structure of 3L1P1 is concluded to be the methyl glycoside of lactosamine trimer (3L1-OMe). The disaccharide fragment ion (m/z 452) in the positive ion ESI-MS/MS spectra of compound 3L1P3 (M+46) exhibited characteristic ions, m/z 305 (m/z 452-CH(OMe)₂CHNHAc-H), which suggested the presence of a dimethyl acetal structure in the reducing end sugar moiety of the hexasaccharide.

Melittin-Diacylphosphatidylcholine Interaction Examined by Electrospray Ionization Fourier Transform Ion Cyclotron Resonance Mass Spectrometry

Satoko AKASHI^{*a), †} and Koji TAKIO^a) (^*a Division of Biomolecular Characterization, RIKEN (The Institute of Physical and Chemical Research) (2-1 Hirosawa, Wako, Saitama, 351-0198, Japan)^* To whom correspondence should be addressed ^† Present address: Graduate School of Integrated Science, Yokohama City University (1-7-29 Suehiro-cho, Tsurumi-ku, Yokohama, Kanagawa 230-0045, Japan) E-mail: akashi@tsurumi.yokohama-cu.ac.jp)

J. Mass Spectrom. Soc. Jpn., 50(2),67-71, 2002

The structure of melittin in the presence of dioleoylphosphatidylcholine (DOPC) was investigated using hydrogen-deuterium (H/D) exchange in conjunction with collision induced dissociation (CID) in an rf-only hexapole ion guide with electrospray ionization-Fourier transform ion cyclotron resonance mass spectrometry (ESI-FT-ICR MS). The deuterium incorporation into backbone amide hydrogens of melittin in the presence of DOPC was analyzed at different time points examining the mass of each fragment ion produced by hexapole-CID. The percentage of deuterium incorporation into the fragments of melittin was less than 45% at initial 10 s of isotope exchange. It increased rapidly as the exchange period was prolonged. After 300 s of incubation in D₂O about 85% of amide hydrogens were exchanged with deuterium. When melittin was incubated in D₂O in the presence of dodecylphosphocholine (DPC), the rate of isotope exchange was reduced at every time point. In the case of melittin alone, more than 80% amide hydrogens were exchanged with deuterium within 10 s. By comparing these time courses, it seems that the contact with DOPC did not induce melittin to change its conformation. DOPC possibly just shielded the melittin molecule while DPC induced melittin to form some stable conformation, such as helical structure. It was revealed that H/D exchange and MS analysis enabled to study such structural changes of a peptide brought about by the interaction with two types of phospholipid even in the presence of 50-fold amount of lipid.

Secondary Ions Produced by 400 eV He⁺ Ions on N₂ and O₂ Thin Films at 8 K

Makoto WATANABE, Tetsuya SATO, Kenzo HIRAOKA, and Kunihiko MORI( Graduate School of Engineering, Yamanashi University (4-3-11 Takeda, Kofu 400-8511, Japan) Clean Energy Research Center, Yamanashi University (4-3-11 Takeda, Kofu 400-8511, Japan))

J. Mass Spectrom. Soc. Jpn., 50(2),72-74, 2002

Secondary ions produced by 400 eV He⁺ ion impact on N₂ and O₂ thin films deposited on a silicon substrate at 8 K were measured as a function of film thickness using a reflectron-type time-of-flight mass spectrometer. While the major ions observed were N_n⁺ with n up to 4 for N₂ film, larger cluster ions of O_n⁺ (n up to 10) were observed. The secondary ion intensities for N₂ and O₂ reached the plateau with film thickness of about 20 and 400 monolayers, respectively. The observed marked difference in the film-thickness dependence between N₂ and O₂ films is discussed on the viewpoint of relaxation of electronic energy deposited in the solid films by the incident 400 eV He⁺ ions.

Unexpected Fragmentation of a Novel Cationic Glycosphingolipid, Glyceroplasmalopsychosine, by Electrospray Ionization and Low Energy Multistage Mass Spectrometry

Keiko TADANO-ARITOMI,^a) Toshiyuki HIKITA,^{b), c)} Takeshi KASAMA,^d) Sen-itiroh HAKOMORI,^{b), c)} and Ineo ISHIZUKA^*a)(^*a) Department of Biochemistry, Teikyo University School of Medicine (Kaga 2-11-1, Itabashi-ku, Tokyo 173-8605, Japan) ^b) Division of Biomembrane Research, Pacific Northwest Research Institute, ^c) Department of Pathobiology, University of Washington (Seattle, Washington 98195-7238, USA) ^d) Instrumental Analysis Research Center for Life Science, Tokyo Medical and Dental University (Bunkyo-ku, Tokyo 113-8510, Japan))

J. Mass Spectrom. Soc. Jpn., 50(2),75-77, 2002

Glyceroplasmalopsychosine, Gro1(3)-O-plasmal-O-6Galβ-sphingosine, is a unique plasmal conjugate of galactosylsphingosine (psychosine) that has an O-acetal conjugate of plasmal to the hydroxyl groups of both glycerol and galactosyl residues. Electrospray ionization ion trap mass spectrometry was applied to the structural analysis of this unique compound. In the MS/MS (MS²) spectrum produced by low energy collision-induced dissociation (CID) of the [M+H]⁺ ion, elimination of glycerol was predominant. MS/MS/MS (MS³) of the [M+H-glycerol]⁺ ion yielded an outstanding anomalous ion which required the loss of a hexose in the middle of the molecule with the plasmal residue retained on the psyhchosine side. This unexpected fragmentation by MS³ could be attributed to a rearrangement of the plasmal residue to the sphingosine residue, allowing elimination of the galactose by subsequent MS³ after CID.