The influence of peptide impurity profiles on functional tissue-organ bath response: the 11-mer peptide INSL6[151-161] case

Bioactive peptides have great pharmaceutical potential as nutraceuticals, diagnostics, and therapeutic drugs in several clinical areas. Thus, the search for novel lead peptides with a biological function has attracted renewed interest. Crude peptide material (i.e., ~70% purity) of INSL6[151-161] (NH₂-FRSLFWGNHSQ-COOH) was found to trigger a contractile response in guinea pig ileum longitudinal smooth muscle preparations using tissue-organ baths. However, the purified peptide (i.e., ≥ 95% purity) had no effect on this model. Further investigation with crude materials from other suppliers, with purities ranging between 50% and 80%, indicated that the crude products gave a false-positive functional tissue-organ bath conclusion. These observations question the functionality conclusions when using crude-purity peptide materials; during the initial research or discovery phase, peptide quality is generally neglected, possibly leading to misinterpretation of biological results due to by-products from peptide synthesis and, thus, wrong fail/pass decisions. Therefore, we strongly recommend appropriate quality control testing before using any peptides for initial biomedical research or discovery purposes.

Ultraviolet photodepletion spectroscopy of dibenzo-18-crown-6-ether complexes with alkaline Earth metal divalent cations

Ultraviolet photodepletion spectra of dibenzo-18-crown-6-ether complexes with alkaline earth metal divalent cations (A(2+)-DB18C6, A = Ba, Sr, Ca, and Mg) were obtained in the gas phase using electrospray ionization quadrupole ion-trap reflectron time-of-flight mass spectrometry. Each spectrum exhibits the lowest energy absorption band in the wavenumber region of 35 400-37 800 cm(-1), which is tentatively assigned as the origin of the S(0)-S(1) transition of A(2+)-DB18C6. This origin band shows a red shift as the size of the metal dication increases from Mg(2+) to Ba(2+). The binding energies of the metal dications to DB18C6 at the S(0) state were calculated at the lowest energy structures optimized by the density functional theory and employed with the experimental energies of the origin bands to estimate the binding energies at the S(1) state. We suggest that the red shifts of the origin bands arise from the decrease in the binding energies of the metal dications at the S(1) state by nearly constant ratios with respect to the binding energies at the S(0) state, which decrease with increasing size of the metal dication. This unique relationship of the binding energies between the S(0) and S(1) states gives rise to a linear correlation between the relative shift of the origin band of A(2+)-DB18C6 and the binding energy of the metal dication at the S(0) state. The size effects of the metal cations on the properties of metal-DB18C6 complex ions are also manifested in the linear plot of the relative shift of the origin band as a function of the size to charge ratio of the metal cations, where the shifts of the origin bands for all DB18C6 complexes with alkali and alkaline earth metal cations are fit to the same line.

Pulsed ion extraction diagnostics in a quadrupole ion trap linear time-of-flight mass spectrometer

Pulsed extraction techniques are investigated for a quadrupole ion trap (QIT) interfaced to a linear time-of-flight (TOF) mass analyzer. A nonfocusing short-pulse mode of operation is developed and characterized. The short-pulse mode creates a near-monoenergetic ion packet, which is useful for reaction kinetics experiments and for making diagnostic measurements of the ion cloud size in the trap. Monopolar and bipolar pulsing modes, with the voltage pulses applied to one or both QIT endcaps to extract the ions into the TOF region, are compared. Ion TOF peak distributions are characterized experimentally and by ion trajectory simulations. Also, first-order spatial (Wiley-McLaren) focusing of ions is characterized for the conventional long-pulse extraction mode. The nonparallel fields in the QIT, which serves as the first acceleration region in the linear-TOF mass spectrometer, are shown to degrade spatial focusing and mass resolution.

Ultraviolet photodissociation at 355 nm of fluorescently labeled oligosaccharides

Ultraviolet photodissociation (UVPD) produces complementary fragmentation to collision-induced dissociation (CID) when implemented for activation of fluorescently labeled oligosaccharide and glycan ions. Reductive amination of oligosaccharides with fluorophore reagents results in efficient photon absorption at 355 nm, producing fragment ions from the nonreducing end that do not contain the appended fluorophore. In contrast to the fragment ions observed upon UVPD (A- and C-type ions), CID produces mainly reducing end fragments retaining the fluorophore (Y-type ions). UVPD affords better isomeric differentiation of both the lacto-N-fucopentaoses series and the lacto-N-difucohexaoses series, but in general, the combination of UVPD and CID offers the most diagnostic elucidation of complex branched oligosaccharides. Four fluorophores yielded similar MS/MS results; however, 6-aminoquinoline (6-AQ), 2-amino-9(10 H)-acridone (AMAC) and 7-aminomethylcoumarin (AMC) afforded more efficient photon absorption and subsequent dissociation than 2-aminobenzamide (2-AB). UVPD also was useful for characterization of glycans released from ribonuclease B and derivatized with 6-AQ. Lastly, electron photodetachment dissociation of oligosaccharides derivatized with 7-amino-1,3-naphthalenedisulfonic acid (AGA) yielded unique cross-ring cleavages similar to those obtained by electron detachment dissociation.

Development of a time-resolved method for photodissociation mechanistic study of protonated peptides: use of a voltage-floated cell in a tandem time-of-flight mass spectrometer

Photodissociation at 266 nm of some protonated peptides was investigated using a tandem-TOF spectrometer equipped with a cell near its first time focal point where the laser was irradiated. When a high voltage was applied to the cell, each product ion peak split into several components with different flight times. One of these was due to in-cell direct formation of the product ion and another due to post-cell formation. Those in between were due to consecutive dissociations, the first steps of which occurred inside the cell and the second steps outside the cell. A method based on flight time calculation was developed to analyze these components and to identify the intermediate ion for each consecutive component. The technique allows time-resolved photodissociation mechanistic studies on a 100-ns timescale.