To determine whether methyl esterification occurs PR-171 purchase with synthetic standards, 2 μL of 10−3 M [Asn13]-orcokinin or Orc[1-11] (NFDEIDRSGFGFN or NFDEIDRSGFG, respectively; GenScript Corporation, Scotch Plain, NJ, USA) was mixed with 30 μL of either CH3OH:water:acetic acid (65:30:5), CD3OD:water:acetic acid (65:30:5), or nanopure water. The solutions sat at room temperature for 23 h before they were dried, reconstituted with 25 μL 1:1 ACN:water,

and analyzed by MALDI-FTMS. To determine whether an exogenous orcokinin peptide undergoes truncation and C-terminal methylation, 1 nmol of a synthetic [Ala13]-orcokinin standard (NFDEIDRSGFGFA, a gift from Drs. L. Li [University of Wisconsin-Madison] and E. Marder [Brandeis University]) was added to two 0.6 mL microcentrifuge tubes, each containing 50 μL of extraction

solvent [CH3OH:water:acetic acid (65:30:5)]. The first tube contained only the solvent and standard; to the second tube, one eyestalk ganglion was added and homogenized. Both samples were sonicated for 5 min and centrifuged for 15 min; the solvent fraction was then analyzed by MALDI-FTMS. The solvent in the tissue-containing samples was analyzed without separating the supernatant from the tissue pellet. An additional 1 nmol of the [Ala13]-orcokinin standard was added to the tissue/extraction solvent mixture, and see more the sample was resonicated and centrifuged and analyzed before and after sitting at room temperature overnight. To determine whether C-terminal methylation can compete with hydrolysis by trypsin, 1 nmol of NFDEIDRAAFGFA was mixed with 0.09 nmol of bovine trypsin (Sigma–Aldrich) in 25 mM, pH = 4.0, citrate buffer prepared with water or 25% methanol. The digestion proceeded at room temperature PD184352 (CI-1040) for 1–4 days with analysis by HPLC Chip–nanoESI Q-TOF MS. Most samples were analyzed

using a HiResMALDI Fourier transform mass spectrometer (Varian, Lake Forest, CA, USA) with a Cryomagnetics (Oak Ridge, TN, USA) 4.7 Tesla actively shielded superconducting magnet. Ions were generated using a pulsed nitrogen laser (337 nm) and were transported from the external ion source to the closed cylindrical ICR cell using a quadrupole ion guide. The ion guide radio frequency potential and trapping delay time were optimized to transmit and trap ions of a selected mass range (optimized for m/z 1500 for the results presented here). A pulse of argon was introduced to the vacuum system during trapping to elevate the system pressure transiently for collisional cooling. All spectra were measured using ion accumulation techniques, where ions from 7 to 30 successive laser shots were accumulated in the cell. A delay of 5–10 s preceded ion detection, which occurred with analyzer pressures of 1–2 × 10−10 Torr.