On-line sample clean-up and chromatography coupled with electrospray ionization mass spectrometry to characterize the primary sequence and disulfide bond content of recombinant calcium binding proteins

We have used on-line sample clean-up, concentration, and chromatography with electrospray ionization mass spectrometry (ESI-MS), to characterize and determine the presence of disulfide bonds in recombinant full-length rat brain calbindin D28K and two deletion mutants of the protein, one lacking EF-hand 2 (calbindin delta 2) and the other lacking EF-hands 2 and 6 (calbindin delta 2,6). The molecular weights of the expressed proteins dissolved in biological buffers were determined with high accuracy using a low-flow, pressurized chamber infusion system, that allows on-line protein clean-up by removing buffers/salts incompatible with ESI-MS. The molecular weight determinations showed that the amino-terminal methionine residues had been cleaved during the expression and isolation of the recombinant proteins. Approximately 85-90% of the protein sequences were confirmed by on-line HPLC-ESI-MS analysis of peptides generated by a lysyl endoproteinase C digestion. Comparisons of ESI-MS spectra of native and reduced calbindin D28K and delta 2 show that the full length- and delta 2 mutant-protein contain one disulfide bond. Molecular mass determinations of calbindin delta 2,6 showed that this protein contains a highly active cysteine residue that covalently binds a mercaptoethanol group, or forms a homodimer via a disulfide bond. The results show surprising differences amongst the deletion mutants of calbindin D28K with respect to the formation of disulfide bonds. These differences are not readily detected by other techniques and show that ESI-MS is a powerful, rapid method by which to detect disulfide linkages for intact proteins.     

Polymerization of vinyl stearate multilayers

A study was made of the solid-state polymerization of built-up monomolecular layers of vinyl stearate. Polymerization was initiated by exposing the samples to ⁶⁰Co γ-radiation. The reactions were followed by multiple internal reflection infrared spectroscopy. The structure of the multilayer monomer and polymer was studied by x-ray diffraction. Surface properties of the multilayers were studied by contact-angle measurements. Results showed that, under the proper conditions, monomer multilayers of vinyl stearate could be polymerized to virtually 100% completion. Reaction was favored by higher irradiation temperatures, larger doses of radiation, and by higher reaction temperatures. The x-ray diffraction photographs indicated that both the monomer and polymer multilayers possessed some single crystal character. Contact-angle measurements indicated that the molecules in both the monomer and polymer multilayers were closely packed.     

The conditions of water absorption when employing an external absorbent in the microdetermination of carbon and hydrogen

Summary The conditions of water absorption when using an external nitrogen dioxide absorbent in the carbon and hydrogen microdetermination are very critical. Two sources of error are considered and effectively eliminated or reduced to insignificance. The resultant modified procedure has an accuracy of % C ±0.35, % H ±0.25.

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Zusammenfassung Die Bedingungen der Wasserabsorption bei Absorption der Stickstoffoxyde außerhalb des Verbrennungsrohres sind für die Mikrobestimmung von Kohlenstoff und Wasserstoff sehr kritisch. Zwei Fehlerquellen wurden erfaßt und wirksam beseitigt bzw. soweit ausgeschaltet, daß sie bedeutungslos sind. Die Genauigkeit des modifizierten Verfahrens beträgt ±0,35% C und ±0,25% H.

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Résumé Lorsque l'on utilise un absorbant externe au peroxyde d'azote les conditions d'absorption de l'eau sont très critiques dans le cas du microdosage du carbone et de l'hydrogène. On considère deux sources d'erreurs et on les élimine effectivement ou on les rend négligeables. Le procédé modifié qui en résulte a une précision en % C de ±0,35 et en % H de ±0,25.

     

A structural model for cyanine dyes templated into the minor groove of DNA

3,3-Diethylthiadicarbocyanine (DiSC₂(5)) is a monocationic dye which forms cofacial dimers that insert into the minor groove of DNA [J. Seifert, R. Conner, S. Kushon, M. Wang, B. Armitage, J. Am. Chem. Soc. 121 (1999) 2987]. These dyes self-assemble into long helical aggregates in AT-rich regions with the dimers aligned in an end-to-end fashion. A model is presented that allows for the construction of large helical aggregates with continuously variable structural parameters. The spectra or excited states are computed using a direct intermediate neglect of differential overlap (INDO) single configuration interaction (SCI) method. Results are reported for both H- and J-type aggregates ranging in size from 2 to 6 dimers. A more approximate model based on transition charge densities enables calculations of larger aggregates. These models are used to derive structural parameters of both H- and J-type aggregates from the available spectral data, resulting in a new structural model for J-type aggregation in these systems.     

Reactions of 2,2,2-trifluorodiazoethane with carbon-nitrogen and carbon-oxygen multiple bonds

2,2,2-Trifluorodiazoethane reacts with trifluoroacetonitrile in the dark at room temperature to give a 2-(2,2,2-trifluoroethyl)-4, 5-bis(trifluoromethyl)triazole, the 1,2,3-triazole structure being preferred to the 1,2,4-isomer on the basis of the ¹⁹F n.m.r. spectrum. The diazoethane reacts more slowly with trichloroacetonitrile, again forming the N-alkylated triazole even in the presence of an excess of the nitrile. No identifiable adduct resulted with acetonitrile. Hexafluoroisopropyl-ideneimine is first N-alkylated and then undergoes addition to form 1-(2,2,2-trifluoro-1-trifluoromethyl)ethyl-4,5-bis(trifluoromethyl)-?-1,2,3-triazoline, but N-methylhexafluoroisopropylideneimine failed to react. Trifluoroacetaldehyde and trichloroacetaldehyde give mixtures of the ketone (formed by insertion of the CF₃CH group into the aldehyde CH bond) and the $\text{cis}$- and $\text{trans}$-oxirans, apparently $\text{via}$ a β-hydroxydiazoalkane.     

Pulsed field-gradient spin echo N.M.R. studies of flow in fluids

An analysis is presented of the effects of various flow patterns on spin echo shapes and amplitudes in the presence of both static and pulsed gradients in the applied magnetic field. Two approaches are used, one based on the Bloch equations, the other on a molecular average picture. In the case of flow patterns with velocity gradients the effects of self-diffusion across these on the N.M.R. experiments is pointed out and shown to be negligible in most cases of interest. Extension of a multipulse sequence for the study of flow to include pulsed field gradients is outlined. Experiments are described which largely confirm the theoretical predictions (except in the case of echo shapes) for plug flow and laminar flow in a circular pipe. The problem of loss of labelled nuclei from the receiver coil during the experiment is treated in detail for the case of laminar flow. The method is applied to a brief study of the flow properties of agar gel as a function of agar concentration. It is shown by using both phase sensitive and diode detectors that the flow pattern changes from laminar at low agar concentration to a sheared plug flow at higher concentrations.     

Reagenzien

Ohne Zusammenfassung     

Fragmentation of an alkali metal-attached peptide probed by collision-induced dissociation fourier transform mass spectrometry and computational methodology.

Collision-induced dissociation of metal-cationized N-CBZ-Gly-Pro-Gly-Pro-Ala was studied by Fourier transform mass spectrometry. Lithium-, sodium-, potassium- and rubidium-cationized peptide species were generated by matrix-assisted laser desorption/ionization (MALDI) using 2,5-dihydroxybenzoic acid as matrix, together with appropriate metal salts. The experimental mass spectrometric results were interpreted with the aid of Monte Carlo conformational searches using the Amber(*) force field, together with ab initio molecular orbital calculations with Gaussian-94 for the singly lithium- and potassium-cationized peptides. It is concluded that metal coordination plays a key role in guiding the gas-phase fragmentation of the cationized peptide. In contrast to lithium and sodium, potassium and rubidium apparently do not coordinate to the C-terminal carbonyl. When the peptide is cationized with the two smaller alkali metals, losses corresponding to alanine and CBZ are observed, while the coordination of potassium and rubidium results in only CBZ loss upon dissociation.