Simplified capillary isoelectric focusing with chemical mobilization for intact protein analysis

We report a capillary isoelectric focusing system based on a sequential injection method for simplified chemical mobilization. This system was coupled to an ion trap mass spectrometer with an electrokinetically pumped nanoelectrospray interface. The nanoelectrospray emitter employed an acidic sheath electrolyte. To simplify focusing and mobilization, a plug of ammonium hydroxide was first injected into the capillary, followed by a section of mixed sample and ampholyte. During focusing, the NH₃ H₂ O section worked as catholyte. As focusing progressed, the NH₃ H₂ O section was titrated to lower pH by the acidic sheath electrolyte. Chemical mobilization started automatically once the ammonium hydroxide was consumed by the acidic sheath flow electrolyte, which then acted as the mobilization solution. In this report, the lengths of the NH₃ H₂ O section and sample were optimized. With a 1 m long capillary, a relative short plug of the NH₃ H₂ O section (3 cm) produced both fast migration and reasonable separation resolution. The simplified capillary isoelectric focusing mass spectrometry system produced base peak intensity relative standard deviation of 8.5% and migration time relative standard deviation ≤0.6% for myoglobin and cytochrome C in triplicate runs.

Adduct formation in liquid chromatography-triple quadrupole mass spectrometric measurement of bryostatin 1

Bryostatin 1, a potential anti-Alzheimer drug, is effective at subnanomolar concentrations. Measurement is complicated by the formation of low m/z degradation products and the formation of adducts with various cations, which make accurate quantitation difficult. Adduct formation caused the sample matrix or mobile phase to partition bryostatin 1 into products of different mass. Degradation of the 927 [M+Na](+) ion to a 869m/z product was strongly influenced by ionization conditions. We validated a bryostatin 1 assay in biological tissues using capillary column HPLC with nanospray ionization (NSI) in a triple-quadrupole mass spectrometer in selected reaction monitoring (SRM) mode. Adduct formation was controlled by adding 1mM acetic acid and 0.1mM sodium acetate to the HPLC buffer, maximizing the formation of the [M+Na](+) ion. Efficient removal of contaminating cholesterol from the sample during solvent extraction was also critical. The increased sensitivity provided by NSI and capillary-bore columns and the elimination of signal partitioning due to adduct formation and degradation in the ionization source enabled a detection limit of 1×10(-18)mol of bryostatin 1 and a LLOQ of 3×10(-18)mol from 1μl of sample. Bryostatin 1 at low pmol/l concentrations enabled measurement in brain and other tissues without the use of radioactive labels. Despite bryostatin 1's high molecular weight, considerable brain access was observed, with peak brain concentrations exceeding 8% of the peak blood plasma concentrations. Bryostatin 1 readily crosses the blood-brain barrier, reaching peak concentrations of 0.2nM, and specifically activates and translocates brain PKCɛ.

Direct analyte-probed nanoextraction coupled to nanospray ionization-mass spectrometry of drug residues from latent fingerprints

Here, we present a method of extracting drug residues from fingerprints via Direct Analyte-Probed Nanoextraction coupled to nanospray ionization-mass spectrometry (DAPNe-NSI-MS). This instrumental technique provides higher selectivity and lower detection limits over current methods, greatly reducing sample preparation, and does not compromise the integrity of latent fingerprints. This coupled to Raman microscopy is an advantageous supplement for location and identification of trace particles. DAPNe uses a nanomanipulator for extraction and differing microscopies for localization of chemicals of interest. A capillary tip with solvent of choice is placed in a nanopositioner. The surface to be analyzed is placed under a microscope, and a particle of interest is located. Using a pressure injector, the solvent is injected onto the surface where it dissolves the analyte, and then extracted back into the capillary tip. The solution is then directly analyzed via NSI-MS. Analyses of caffeine, cocaine, crystal methamphetamine, and ecstasy have been performed successfully.

Mass spectrometric study of the Escherichia coli repressor proteins, Ic1R and Gc1R, and their complexes with DNA

In Escherichia coli, the IclR protein regulates both the aceBAK operon and its own synthesis. Database homology searches have identified many IclR-like proteins, now known as the IclR family, which can be identified by a conserved C-terminal region. We have cloned and purified one of these proteins, which we have named GclR (glyoxylate carboligase repressor). Although purification is straightforward, both the IclR and GclR proteins are difficult to manipulate, requiring high salt (up to 0.6 M KCl) for solubility. With the advent of nanospray ionization, we could transfer the proteins into much higher concentrations of volatile buffer than had been practical with ordinary electrospray. In 0.5 M ammonium bicarbonate buffer, both proteins were stable as tetramers, with a small amount of dimer. In a separate experiment, we found that IclR protein selected from a random pool a sequence which matched exactly that of the presumed binding region of the GclR protein, although IclR does not regulate the gcl gene. We designed a 29 bp synthetic DNA to which IclR and GclR bind, and with which we were able to form noncovalent DNA-protein complexes for further mass spectrometry analysis. These complexes were far more stable than the proteins alone, and we have evidence of a stoichiometry which has not been described previously with (protein monomer : dsDNA) = (4 : 1).