title: Capillary LC-MS2 at the attomole level for monitoring and discovering endogenous peptides in microdialysis samples collected in vivo.
abstract: Fused-silica capillary LC columns (25-microm i.d.) with 3-microm-i.d. integrated electrospray emitters interfaced to a quadrupole ion trap mass spectrometer were evaluated for high-sensitivity LC-MS2. Column preparation involved constructing frits by in situ photopolymerization of glycidyl methacrylate and trimethylolpropane trimethacrylate, preparing the electrospray emitter by pulling the column outlet to a fine tip with a CO2 laser puller, and slurry-packing the column with 5-microm reversed-phase particles. Large-volume injections were facilitated by an automated two-pump system that allowed high-flow rates for sample loading and low-flow rates for elution. Small electrospray emitters, low elution flow rates, and optimization of gradient steepness allowed a detection limit of 4 amol, corresponding to 2 pM for 1.8 microL injected on-column, for a mixture of peptides dissolved in artificial cerebral spinal fluid. The system was coupled on-line to microdialysis sampling and was used to monitor and discover endogenous neuropeptides from the globus pallidus of anesthetized male Sprague-Dawley rats. Time-segmented MS2 scans enabled simultaneous monitoring of Met-enkephalin, Leu-enkephalin, and unknown peptides. Basal dialysate levels of Met-enkephalin and Leu-enkephalin were 60 +/- 30 and 70 +/- 20 pM while K+-stimulated levels were 1,900 +/- 500 and 1,300 +/- 300 pM, respectively (n = 7). Data-dependent and time-segmented MS2 scans revealed several unknown peptides that were present in dialysate. One of the unknowns was identified as peptide I(1-10) (SPQLEDEAKE), a novel product of preproenkephalin A processing, using MS2, MS3, and database searching.
authors.affiliation: Department of Chemistry, University of Florida, Gainesville 32611-7200, USA.
authors.forename: W E
authors.initials: WE
authors.lastname: Haskins
authors.forename: Z
authors.initials: Z
authors.lastname: Wang
authors.forename: C J
authors.initials: CJ
authors.lastname: Watson
authors.forename: R R
authors.initials: RR
authors.lastname: Rostand
authors.forename: S R
authors.initials: SR
authors.lastname: Witowski
authors.forename: D H
authors.initials: DH
authors.lastname: Powell
authors.forename: R T
authors.initials: RT
authors.lastname: Kennedy
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002851:Chromatography, High Pressure Liquid / Q000295:instrumentation* / Q000379:methods*; D004745:Enkephalins / Q000737:chemistry / Q000378:metabolism; D008297:Male; D017551:Microdialysis / Q000295:instrumentation* / Q000379:methods*; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000032:analysis; D010455:Peptides / Q000737:chemistry / Q000302:isolation & purification*; D011498:Protein Precursors / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D021241:Spectrometry, Mass, Electrospray Ionization / Q000295:instrumentation* / Q000379:methods*
chemical_list: D004745:Enkephalins; D010446:Peptide Fragments; D010455:Peptides; D011498:Protein Precursors; C033660:preproenkephalin