Analysis of protein digests by capillary high-performance liquid chromatography and on-line fast atom bombardment mass spectrometry

Instrumental requirements for nanoscale liquid chromatography

Nanoscale liquid chromatography (nano-LC), with packed columns of typically 75 μm i.d. × 15 cm length, packed with C18, 5 μm of stationary phase, and optimal flow rates of 180 nL/min, can be considered as a miniaturized version of conventional HPLC. Using the down-scaling factor, which corresponds to the ratio of the column diameter in square, (d(conv)/d(micro))(2), excellent agreement between the theoretically calculated values and the values obtained using the down-scaling factor (∼3800) has been observed. This factor was applied to all system components, including flow rate, injection and detection volumes, and connecting capillaries. Down-scaling of a conventional HPLC system to a nano-LC system is easy to realize in practice and involves using a microflow processor for nanoflow delivery (50-500 nL/min), a longitudinal nanoflow cell (≤3 nL), a microinjection valve (≤ 20 nL), low-dispersion connecting tubing, and zero dead volume connections. Excellent retention time reproducibility was measured with RSD values of ±0.1% for isocratic and ±0.2% for gradient elution. Plates counts of more than 100 000/m indicate the excellent performance of the entire nano-LC system. With minimal detectable amounts of proteins in the low femtomole and subfemtomole ranges (e.g., 520 amol for bovine serum albumin), high mass sensitivity was found, making nano-LC attractive for the microcharacterization of valuable and/or minute proteinaceous samples. Coupling nano-LC with concomitant mass spectrometry using nanoscale ion spray or electrospray interfaces looks very promising and is obviously the next step for future work.

The future of proteomic analysis in biological systems and molecular medicine

Proteomics is the study of proteins and their interactions within complex biological systems. While this field is often associated with mass spectrometry, it is more useful to consider proteomics in the context of an objective: to identify and understand the molecular basis of health and disease at the protein level in vivo. Achieving this objective will require (1) technological developments to resolve current instrument limitations and (2) multidisciplinary integration of biological and protein analysis technologies to answer important questions in both the biological sciences and molecular medicine.

Proteomic LC-MS systems using nanoscale liquid chromatography with tandem mass spectrometry

Current nano-scale liquid chromatography-tandem mass spectrometry (nanoLC-MS/MS) approaches in proteome research are reviewed from an analytical perspective. For comprehensive analysis of cellular proteins, analytical methods with higher resolution, sensitivity, and wider dynamic range are required. Miniaturized LC coupled with tandem mass spectrometry is currently one of the most versatile techniques. In this review, the current status of nanoLC-MS/MS systems as well as data management systems is addressed. In addition, the future prospects for complete proteomics are discussed.

Using accurate mass electrospray ionization-time-of-flight mass spectrometry with in-source collision-induced dissociation to sequence peptide mixtures

Although data-dependent LC-MS-MS with database searching has become au courant for identifying proteins, the technique is constrained by duty-cycle inefficiency and the inability of most tandem mass analyzers to accurately measure peptide product ion masses. In this work, a novel approach is presented for simultaneous peptide fragmentation and accurate mass measurement using in-source collision-induced dissociation (CID) on electrospray ionization (ESI)-time-of-flight (TOF) MS. By employing internal mass reference compounds, mass measurement accuracy within +/-5 ppm for tryptic peptide precursors and +/-10 ppm for most sequence-specific product ions was consistently achieved. Analysis of a complex solution containing several digested protein standards did not adversely affect instrument performance.

A simplified gradient solvent delivery system for capillary liquid chromatography-electrospray ionization mass spectrometry

We describe a simple solvent delivery system for gradient capillary HPLC at nanoliter per minute flow rates. The novel aspect of the system is that solvents are delivered one at a time, using a switching valve, into a relatively large-volume mixing chamber. Efficient mixing in the chamber causes the formation of a sigmoidal gradient from the initial solvent to the subsequent solvent, which is then delivered to a capillary column. The shape of the gradients formed can be predicted from a simple theoretical model. Gradients of different slope can be formed by varying either the size of the chamber or the system flow rate. The system is robust, reproducible, and simple to operate. We provide a detailed protocol of how to construct a low-cost capillary HPLC system consisting of two syringe pumps, a capillary mixing chamber, a capillary column, and a zero dead-volume microelectrospray interface. We demonstrate that the coupling of this HPLC system to a mass spectrometer enabled us to identify proteins at the low femtomole level in solution-phase digests and at the picomole level in digests of samples separated on SDS-PAGE gels. We believe that the strategy presented will be useful as a general method for the characterization of proteins and peptides by capillary HPLC-electrospray mass spectrometry.

Mouse RAD50 has limited epitopic homology to p53 and is expressed in the adult myocardium

Previous studies have identified a 180-kDa mouse cardiomyocyte phosphoprotein with limited epitopic homology to p53. In this study, the protein was purified and partially sequenced. Oligonucleotide probes based on the available amino acid sequence data were used to isolate cDNA clones. Sequence analyses revealed that the clones encoded a protein with regional homology to the yeast RAD50 gene product. Expression of the mouse cDNA rescued the methyl methanesulfonate-sensitive phenotype in rad50 mutant yeast, indicating that the cardiomyocyte phosphoprotein is the mammalian homologue of the yeast RAD50 gene product. Fluorescence in situ hybridization analyses localized the mouse RAD50 gene to the A5-B1 region of chromosome 11. Northern blot analyses demonstrated a complex pattern of RAD50 expression during mouse development which was further complicated by the presence of several alternatively spliced transcripts. High levels of RAD50 expression was evident in the adult myocardium, a somewhat surprising observation given the absence of DNA synthesis in adult cardiomyocytes.

Cloning, sequencing, and expression of a 24-kDa Ca(2+)-binding protein activating photoreceptor guanylyl cyclase

Two vertebrate photoreceptor-specific membrane guanylyl cyclases, RetGC-1 and RetGC-2, are activated by a soluble 24-kDa retinal protein, p24, in a Ca(2+)-sensitive manner (Dizhoor, A.M., Lowe, D.G., Olshevskaya, E.V., Laura, R.P., and Hurley, J.B. (1994) Neuron 12, 1345-1352; Lowe, D.G., Dizhoor, A.M., Liu, K., Gu, O., Laura, R., Lu, L., and Hurley, J.B. (1995) Proc. Natl. Acad. Sci. U.S.A. 92, 5535-5539). The primary structure of bovine p24 has been derived from peptide sequencing and from its cDNA. p24 is a new EF-hand-type Ca(2+)-binding protein, related but not identical to another guanylyl cyclase-activating protein, GCAP (Palczewski, K., Subbaraya, I., Gorczyca, W.A., Helekar, B.S., Ruiz, C.C., Ohguro, H. Huang, J., Zhao, X., Crabb, J.W., Johnson, R.S., Walsh, K.A., Gray-Keller, M.P., Detwiler, P.B., and Baehr, W. (1994) Neuron 13, 395-404) and other members of the recovering family of Ca(2+)-binding proteins. Antibodies against a truncated fusion protein and against a p24-specific synthetic peptide specifically recognize retinal p24 on immunoblot. Both antibodies inhibit activation of photoreceptor membrane guanylyl cyclase by purified p24. p24 is found only in retina, and it copurifies with outer segment membranes. Immunocytochemical analysis shows that it is present in rod photoreceptor cells. An immobilized antibody column was used to purify p24 from a heat-treated retinal extract. Purified p24 appears on SDS-polyacrylamide gel electrophoresis as a homogeneous protein not contaminated with GCAP, and it activates photoreceptor guanylyl cyclase in vitro at submicromolar concentrations. Ca2+ inhibits this activation with an EC50 near 200 nM and a Hill coefficient of 1.7. Recombinant p24 expressed in 293 cells effectively stimulates photoreceptor guanylyl cyclase. These findings demonstrate that p24, like GCAP, imparts Ca2+ sensitivity to photoreceptor membrane guanylyl cyclase. We propose that p24 be referred to as GCAP-2 and that GCAP be referred to as GCAP-1.

Capillary reversed-phase high-performance liquid chromatographic determination of acetyl-methylprednisolone in feline spinal cord

Capillary reversed-phase high-performance liquid chromatography (RP-HPLC) was used to determine acetylmethylprednisolone (A-MP) that had been administered to feline spinal cord tissue. The method used a 300 mm x 0.32 mm I.D. packed capillary octadecylsilyl (ODS) column and an isocratic mobile phase of 40 mM triethylamine formate (TEAF, pH 3.2)-acetonitrile (50:50, v:v). The chromatographic behavior of A-MP was evaluated with respect to peak-area and peak-height by varying the A-MP concentration (12-190 microM) with a fixed injection volume (1 microliter), and by varying the injection volume (1-10 microliter) with a fixed concentration (12 microM) of A-MP. The limit of detection (signal-to-noise ratio, 3:1) was 250 pg (600 fmol) of synthetic A-MP. Various amounts of A-MP directly spiked into feline spinal cord segments were solvent extracted, separated, and plotted against peak-area (r2 = 1.00). Background tissue without A-MP gives minimal (< 1%) interference at 243 nm. The method also detects exogenous A-MP that was administered into feline spinal cord via an intrathecal injection. Furthermore, the presence of A-MP was confirmed via its molecular ion and corresponding product ions that were obtained by fast-atom bombardment tandem mass spectrometry (FAB-MS-MS).

Cloning of AL-1, a ligand for an Eph-related tyrosine kinase receptor involved in axon bundle formation

REK7 is an Eph-related tyrosine kinase receptor expressed exclusively in the nervous system, predominantly in hippocampus and cortex. A soluble REK7-IgG fusion protein, produced to analyze the biological role of REK7, prevents axon bundling in cocultures of cortical neurons with astrocytes, a model of late stage nervous system development and differentiation. Using REK7-IgG as an affinity reagent, we purified and cloned a novel REK7 ligand called AL-1, a GPI-linked protein homologous to other members of an emerging ligand family. Membrane attachment of AL-1 appears necessary for receptor activation, since REK7 on cortical neurons is efficiently activated by transfected cells expressing GPI-linked AL-1, but not by soluble AL-1. Consistent with this, soluble AL-1 blocks axon bundling. Our findings, together with the observation that both molecules are expressed in the brain, suggest a role in the formation of neuronal pathways, a crucial feature of nervous system development and regeneration.

Application of capillary high-performance liquid chromatography to biotechnology, with reference to the analysis of recombinant DNA-derived human growth hormone

Using capillary HPLC, femtomole amounts of recombinant DNA-derived human growth hormone (rhGH) have been successfully detected from solutions at nanomolar concentrations. The separation used capillaries of 15 cm x 320 microns I.D. and detection was with a UV absorbance detector containing a capillary Z-shaped flow-cell. A sample of rhGH that was recovered from rat serum was analyzed by capillary reversed-phase HPLC, using both acidic- and neutral-pH mobile phases, as well as by capillary ion-exchange chromatography. When compared to HPLC separations performed at flow-rates of 1 ml/min, the sensitivity of the detection was increased 200 times, without any loss in resolution. Sub-microgram amounts of rhGH were also analyzed by tryptic mapping using capillary HPLC and peptides were identified by capillary LC-MS.

An interleukin-4-induced transcription factor: IL-4 Stat

Interleukin-4 (IL-4) is an immunomodulatory cytokine secreted by activated T lymphocytes, basophils, and mast cells. It plays an important role in modulating the balance of T helper (Th) cell subsets, favoring expansion of the Th2 lineage relative to Th1. Imbalance of these T lymphocyte subsets has been implicated in immunological diseases including allergy, inflammation, and autoimmune disease. IL-4 may mediate its biological effects, at least in part, by activating a tyrosine-phosphorylated DNA binding protein. This protein has now been purified and its encoding gene cloned. Examination of the primary amino acid sequence of this protein indicates that it is a member of the signal transducers and activators of transcription (Stat) family of DNA binding proteins, hereby designated IL-4 Stat. Study of the inhibitory activities of phosphotyrosine-containing peptides derived from the intracellular domain of the IL-4 receptor provided evidence for direct coupling of receptor and transcription factor during the IL-4 Stat activation cycle. Such observations indicate that IL-4 Stat has the same functional domain for both receptor coupling and dimerization.

Structural characterization of modified nucleosides in tRNA hydrolysates by frit-fast atom bombardment liquid chromatography/mass spectrometry

Feasibility for the structural characterization of modified nucleosides in transfer RNA at low microgram levels has been investigated by using continuous-flow frit-fast atom bombardment liquid chromatography/mass spectrometry (frit-FAB LC/MS). Sample of tRNA(Phe) from brewer's yeast (Saccharomyces cerevisiae) was used as a main model, and enzymatically hydrolysed by nuclease P1 and alkaline phosphatase. The resulting nucleoside mixture was separated by using a microbore reversed-phase LC column (150 mm x 0.5 mm i.d.) with an aqueous ammonium acetate-methanol gradient, and the mass spectra were acquired on both positive and negative ionization modes. The modified nucleosides were characterized by comparison of the relative LC elution times with authentic nucleosides, and further confirmed by the structural information from the frit-FAB mass spectra where both molecular and base ions were in general observed as intense peaks in both ionization modes. Typically, 0.06-0.2 A260 units (3-10 micrograms) of isoaccepting tRNA was enough to obtain full-scan mass spectra of modified nucleosides, often occurring at a frequency of one per tRNA molecule using positive ion detection. The LC/MS system was used to screen modified nucleosides in tRNA of the extremely thermophilic microorganism Pyrodictium occultum.

Microbore reversed-phase high-performance liquid chromatographic purification of peptides for combined chemical sequencing-laser-desorption mass spectrometric analysis

An optimized microbore RP-HPLC system (1.0 mm I.D. columns) for the purification of low picomole amounts (< 5 pmol) of peptides is described. It is comprised of commercially available columns, instrument components and parts. These were selected on the basis of a comparative evaluation and to yield the highest resolution and most efficient peak collection. The sensitivity of this system equals, probably surpasses, that of advanced chemical microsequencing for which 2-4 pmol of peptide are minimally required. As an automated sequencer cannot be "on-line" connected with a micro-preparative HPLC system, fractions must be collected and transferred. With a typical flow of 30 microliters, efficient manual collection is possible and fractions (about 20 microliters in volume) can still be handled without unacceptable losses, albeit with great precaution. Furthermore, major difficulties were encountered to efficiently and quantitatively load low- or sub-picomole amounts of peptide mixtures onto the RP-HPLC column for separation. Discipline and rigorous adherence to sample handling protocols are thus on order when working at those levels of sensitivity. With adequate instrumentation and handling procedures in place, we demonstrate that low picomole amounts of peptides can now be routinely prepared for analysis by combined Edman-chemical sequencing-matrix-assisted laser-desorption mass spectrometry (MALDI-MS). The integrated method was applied to covalent structural characterization of minute quantities of a gel-purified protein of known biological function but unknown identity. The results allowed unambiguous identification and illustrated the power of MALDI-MS-aided interpretation of chemical sequencing data: accurate peptide masses were crucial for (i) confirmation of the results, (ii) deconvolution of mixed sequences, (iii) proposal of complete structures on the basis of partial sequences, and (iv) confirmation of protein identification (obtained by database search with a single, small stretch of peptide sequence) by "mass matching" of several more peptides with predicted proteolytic fragments.

Binding of L-selectin to the vascular sialomucin CD34

The adhesive interactions between leukocyte L-selectin and the endothelium are involved in the migration of lymphocytes through peripheral lymph nodes and of neutrophils to sites of inflammation. A recombinant L-selectin stains high endothelial venules (HEVs) in lymph nodes and recognizes sulfated carbohydrates found on two endothelial glycoproteins, Sgp50 and Sgp90. Amino acid sequencing of purified Sgp90 revealed a protein core identical to that CD34, a sialomucin expressed on hematopoietic stem cells and endothelium. A polyclonal antiserum to recombinant murine CD34 stains peripheral lymph node endothelium and recognizes Sgp90 that is functionally bound by L-selectin. Thus, an HEV glycoform of CD34 can function as a ligand for L-selectin.

Rapid analysis of enzymatic digests of a bacterial protease of the subtilisin type and a "bio-engineered" variant by high-performance liquid chromatography-frit fast atom bombardment mass spectrometry

Amino acid sequencing of a subtilisin-type bacterial protease and a bio-engineered variant was carried out by investigating various enzymatic digests using HPLC-frit fast atom bombardment MS methods. The fast atom bombardment mass spectral data allowed rapid identification of the enzymatically generated peptides and differentiation between both proteins. The feasibility of determining the positions and nature of mutations in the amino acid sequence depends mainly on the size of the peptides containing the modifications.

Peptide mapping of recombinant human interferon-gamma by reversed-phase liquid chromatography with on-line identification by thermospray mass spectrometry and UV absorption spectrometry

The detection and identification of minor peaks in a complex peptide map of recombinant human interferon-gamma was realized by on-line analysis of the eluted peptides using thermospray mass spectrometry and UV absorbance spectrometry. By this procedure the time-consuming process of collection, purification and chemical sequence analysis is avoided. Owing to the formation of multiple charged ions, the domain of the covered masses is extended. Fragmentation of the peptides in the thermospray source was observed resulting from, amongst others, cleavage by acid hydrolysis of peptide bonds involving an aspartic acid. This was of great use for the identification of peptides in a digest of recombinant human interferon-gamma by Staphylococcus aureus strain V8 endoprotease.

Mass spectrometry of proteins and peptides in biotechnology

Recent technological developments in the field of mass spectrometry have resulted in enhanced performance in traditional biotechnological applications and are opening up new approaches to a wide range of problems in protein analysis. Developments in the area of interfacing mass spectrometry with high-resolution separation techniques and the observation of non-covalent interactions and protein conformational changes by mass spectrometry represent notable advances in the past year.

Analytical and micropreparative peptide mapping by high performance liquid chromatography/electrospray mass spectrometry of proteins purified by gel electrophoresis

We report the use of microbore reverse-phase high performance liquid chromatography connected on-line to an electrospray mass spectrometer for the separation/detection of peptides derived by proteolytic digestion of proteins separated by polyacrylamide gel electrophoresis. A small fraction (typically 10% of the total) of the peptides eluting from the column was diverted through a flow-splitting device into the ion source of the mass spectrometer, whereas the majority of the peptide samples was collected for further analyses. We demonstrate the feasibility of obtaining reproducible peptide maps from submicrogram amounts of protein applied to the gel and good correlation of the signal detected by the mass spectrometer with peptide detection by UV absorbance. Furthermore, independently verifiable peptide masses were determined from subpicomole amounts of peptides directed into the mass spectrometer. The method was used to analyze the 265-kDa and the 280-kDa isoforms of the enzyme acetyl-CoA carboxylase isolated from rat liver. The results provide compelling evidence that the two enzyme isoforms are translation products of different genes and suggest that these approaches may be of general utility in the definitive comparison of protein isoforms. We furthermore illustrate that knowledge of peptide masses as determined by this technique provides a major advantage for error-free data interpretation in chemical high-sensitivity peptide sequence analysis.

Identifying proteins from two-dimensional gels by molecular mass searching of peptide fragments in protein sequence databases

A rapid method for the identification of known proteins separated by two-dimensional gel electrophoresis is described in which molecular masses of peptide fragments are used to search a protein sequence database. The peptides are generated by in situ reduction, alkylation, and tryptic digestion of proteins electroblotted from two-dimensional gels. Masses are determined at the subpicomole level by matrix-assisted laser desorption/ionization mass spectrometry of the unfractionated digest. A computer program has been developed that searches the protein sequence database for multiple peptides of individual proteins that match the measured masses. To ensure that the most recent database updates are included, a theoretical digest of the entire database is generated each time the program is executed. This method facilitates simultaneous processing of a large number of two-dimensional gel spots. The method was applied to a two-dimensional gel of a crude Escherichia coli extract that was electroblotted onto poly(vinylidene difluoride) membrane. Ten randomly chosen spots were analyzed. With as few as three peptide masses, each protein was uniquely identified from over 91,000 protein sequences. All identifications were verified by concurrent N-terminal sequencing of identical spots from a second blot. One of the spots contained an N-terminally blocked protein that required enzymatic cleavage, peptide separation, and Edman degradation for confirmation of its identity.

Reversed-phase capillary high-performance liquid chromatography with on-line UV, fluorescence and electrospray ionization mass spectrometric detection in the analysis of peptides and proteins

Analysis of peptide mixtures by reversed-phase capillary HPLC with gradient elution using three detectors in series: UV (214 nm), fluorescence (lambda exc. = 280 nm, lambda emiss. = 356 nm), and electrospray ionization mass spectrometry (ES-MS) is reported. The chromatographic integrity of the system and the detection limits were evaluated. The effect of the mass spectrometer's acquisition rate on the total ion current (TIC) profile was also examined. The utility of fluorescence monitoring with UV and ES-MS detection was demonstrated in the analysis of proteolytic digests of proteins. The native fluorescence character of tryptophan-containing peptides provides selectivity in peptide mapping, while monitoring UV absorption at 214 nm affords detection of the peptide bond. Three tryptophan-containing tryptic peptides of bovine serum albumin were immediately located by fluorescence among many UV peaks and ES-MS provided molecular masses allowing the peptides to be identified.

Semi-quantitative analysis of cefaclor in human serum by capillary high performance liquid chromatography/fast atom bombardment mass spectrometry

Capillary high performance liquid chromatography (HPLC) was combined with frit fast atom bombardment (FAB) mass spectrometry (MS) and a detailed procedure has been established for on-line analysis of cefaclor in human serum. The capillary column (0.3 mm i.d.) enabled the introduction of entire effluent to the frit interface for FAB-MS; and a special column switching device for injection and concentration enabled the injection of as large as a 500-microliters volume sample. These conditions gave much higher sensitivity than that of previous HPLC/MS system. Thus, low levels of cefaclor could be successfully identified in sera by its mass spectral measurements 2 h after its single oral administration of a 250-mg capsule in two subjects.

Packed capillary liquid chromatography coupled to fluorescence detection: application to human blood samples for the determination of glutathione

The present investigation analyses the potentials of capillary chromatography using packed fused silica capillaries filled with 5 microns RP-18 for the fluorescence determination of glutathione in human blood samples. Adaptation of conventional HPLC equipment for miniaturized chromatographic assays proved successful. Sample preparation was relatively simple, though care should be taken in sample handling. The thiolic compound mercaptoethanol was used as internal standard. Qualitative determinations were based on standard addition providing increased peak heights at identical retention times. Quantitative determinations gave linear calibration curves, with a standard glutathione recovery of 98.9% and an intra-assay reproducibility of 3.3%. The glutathione values measured appeared within the normal range of 0.9-1.7 mmol glutathione per litre of blood.

Application of capillary reversed-phase high-performance liquid chromatography to high-sensitivity protein sequence analysis

A continuous gradient elution method for capillary column (less than 0.32 mm I.D.) liquid chromatography was developed. Gradient eluent from a microbore liquid chromatograph was split ahead of the injector so that an accurate percentage (2-3%) of the mobile phase delivered by the pump flowed through the capillary column. The outlet of the column was connected to a length of 0.075 mm I.D. fused-silica capillary tubing which, in turn, was connected to a 6-mm optical path length longitudinal capillary flow cell. Fused-silica capillary columns of 0.32 mm I.D. were slurry-packed efficiently with 7-microns spherical, 300 A pore size, C8 bonded-phase particles, and evaluated in terms of their ability to resolve mixtures of proteins, peptides or phenylthiohydantoin (PTH)-amino acid derivatives. The gradient elution profiles agreed with those obtained using microbore (less than 2.1 mm I.D.) and larger bore columns. The minimum detectable amounts for proteins and PTH-amino acids on 0.32 mm I.D. capillary columns were 50 pg and 25 fmol, respectively. At a flow-rate of 3.6 microliters/min, proteins and peptides were recovered from the capillary columns in volumes of about 2-8 microliters. The use of a multiple-wavelength, forward-optics detector for identifying tryptophan- and tyrosine-containing peptides is discussed.

High Level Escherichia coli Expression and Production of a Bivalent Humanized Antibody Fragment

Many clinical uses of antibodies will require large quantities of fragments which are bivalent and humanized. We therefore attempted to generate humanized F(ab')2 fragments by secretion from E. coli. Titers of 1-2 g l-1 of soluble and functional Fab' fragments have been routinely achieved as judged by antigen-binding ELISA. Surprisingly, this high expression level of Fab' in the periplasmic space of E. coli does not drive dimerization. However, we have developed a protocol to directly and efficiently recover Fab' with the single hinge cysteine in the free thiol state, allowing F(ab')2 formation by chemically-directed coupling in vitro. The E. coli derived humanized F(ab')2 fragment is indistinguishable from F(ab')2 derived from limited proteolysis of intact antibody in its binding affinity for the antigen, p185HER2, and anti-proliferative activity against the human breast tumor cell line, SK-BR-3, which over-expresses p185HER2. This system makes E. coli expression of bivalent antibody fragments for human therapy (or other uses) practical.

Coaxial continuous flow fast atom bombardment for higher-molecular-weight peptides: comparison with static fast atom bombardment and electrospray ionization

A comparison of coaxial continuous flow fast atom bombardment (FAB) with static FAB and with electrospray ionization (ESI) for the analysis of 'high'-mass peptides (Mr = 3000-4000) is presented. Sensitivities of the peptides by coaxial continuous flow FAB is nearly an order of magnitude better than by static FAB. Single-scan spectra with good signal-to-noise can be obtained from as little as 200 fmol (by flow injection analysis). Detection limits by ESI mass spectrometry were found to be equivalent to 20 times higher than by coaxial continuous flow FAB on a per mole basis, but 4-20 times lower on a concentration basis, owing to the greater flow per unit time employed in the ESI mass spectrometric experiments.

Recent advances in liquid chromatography-mass spectrometry and capillary zone electrophoresis-mass spectrometry for protein analysis

The utility of the combination of separations techniques, such as liquid chromatography and capillary zone electrophoresis, with mass spectrometry in applications involving protein analysis is discussed. The use of continuous-flow fast atom bombardment and electrospray ionization mass spectrometry is compared for the analysis of tryptic digests. For liquid chromatography, both microbore and slurry-packed capillary bore columns were used to separate peptides from proteolytic digests.

Rapid confirmation and revision of the primary structure of bovine serum albumin by ESIMS and Frit-FAB LC/MS

Incorrectness of the amino acid sequence of bovine serum albumin (BSA) was suggested from the observed molecular weight of BSA obtained by electrospray ionization mass spectrometry (ESIMS). Lack of a tyrosine residue in the position of 156th was found rapidly, by the combination of frit-fast atom bombardment mass spectrometry/liquid chromatography (Frit-FAB LC/MS), automated Edman degradation and tandem mass spectrometry (MS). Then it turned out that BSA is composed of 583 amino acid residues, and that its average molecular weight is not 66267.1, and it is corrected to 66430.3. Moreover the amino acid sequence of the positions of 94th and 95th was corrected to -QE- by using automated Edman degradation method.

Analysis of proteins and glycoproteins at the picomole level by on-line coupling of microbore high-performance liquid chromatography with flow fast atom bombardment and electrospray mass spectrometry: a comparative evaluation

A comparison of continuous-flow fast atom bombardment (FAB) mass spectrometry and nebulization-assisted electrospray for analysis of proteins and glycoproteins by high-performance liquid chromatography (HPLC)/mass spectrometry is presented. The evaluation was made using enzymatic digests of recombinant soluble CD4 glycoprotein and recombinant hepatitis B surface antigen and a mixture of HPLC retention standard peptides. These samples were analyzed by reversed-phase HPLC on a microbore (1 x 100 mm C18) gradient HPLC system with 10% or 20% of the eluent containing approximately 20-100 pmol of the sample directed into the continuous-flow FAB mass spectrometric or electrospray mass spectrometric source, respectively. The techniques were evaluated on the criteria of chromatographic integrity, ease of data analysis, protein sequence coverage, discrimination effects, ability to detect glycopeptides, simplicity of operation, and sensitivity. Both techniques produce useful peptide molecular weight data from comparable amounts of sample injected. However, the nebulization-assisted electrospray system is capable of yielding higher peptide mapping coverages with the least sample consumed in toto due in part to the wider mass ranges resulting from the multicharging effect and to the ability to detect glycopeptides. Under the experimental conditions employed here no fragmentation was observed in the electrospray mass spectra. In contrast, significant, sequence informative fragmentation was occasionally observed for peptides in the continuous-flow FAB mass spectral data.

Structural characterization by mass spectrometry of native and recombinant human relaxin

Mass spectrometry has played a key role in characterizing the primary structure of native and recombinant relaxin, a peptide hormone that induces ripening of the cervix prior to childbirth. The peptide is composed of two chains, A and B, and is formed from a single-chain prohormone, as is insulin. Aside from conserved cysteines, though, it has little sequence homology with insulin. Due to the small amounts of native peptide initially available (less than 10 pmol), traditional techniques could not provide information on the blocked A-chain sequence, on the carboxyterminal sequences, nor on other possible post-translational modifications. Mass measurements by fast atom bombardment (FAB) were made on reduced human relaxin isolated from corpora lutea. The detection limit by FAB for reduced relaxin was 500 fmol. The B-chain was four amino acids shorter than expected from comparison of the previously known cDNA sequence with homologous rat and porcine sequences. The A-chain, as predicted, was 24 amino acids in length and had a pyroglutamic acid residue on the amino-terminus. The purified samples were homogeneous with no other post-translational modifications. The recombinant relaxin molecule was also extensively characterized by mass spectrometry. In addition to the intact molecule, all tryptic peptides were characterized by FAB. A capillary high-performance liquid chromatography continuous-flow FAB system, developed for high-sensitivity peptide mapping, aided in these analyses. Finally, the three disulfide bonds were shown by tandem mass spectrometry to match those of insulin.