Charge-state shifting of individual multiply-charged ions of bovine albumin dimer and molecular weight determination using an individual-ion approach

Ion-molecule reactions of individual multiply-protonated ions of bovine albumin dimer, formed from electrospray ionization, have been studied using a Fourier transform ion cyclotron resonance mass spectrometer. Upon reaction of ammonia with a group of individual ions, charge-state shifting was observed due to proton transfer. Repeated additions of ammonia during remeasurements of the same ion population were observed to induce multiple-step charge-state shifts. Charge-state-dependent reactivity, as well as nonstatistical behavior in reactivity, was observed due to the small ion population. The molecular weights of individual ions whose charge state shifted during reaction were determined with an accuracy of 67 ppm, the first example of using an individual-ion approach to the determination of molecular weight for a large biopolymer. The molecular weight distribution of a group of ions can be determined with a precision related to the number of ions examined and the weight heterogeneity of the sample. We obtained the molecular weight for eight individual ions from which a molecular weight of 133,320 +/- 210 Da was calculated for bovine albumin dimer.

The anti-proliferative action of transforming growth factor-beta 1 on a rat intestinal epithelial cell line (RIE-1) is dependent on cell population density and culture passage number

1. The proliferation of RIE-1 rat intestinal epithelial cells was potently but reversibly inhibited by transforming growth factor-beta 1 (TGF-beta 1). In early-passage cultures, complete growth arrest was observed when sparse cultures were treated with TGF-beta 1 (1 ng/ml). 2. However, increasing the initial cell culture density resulted in decreased TGF-beta 1-mediated inhibition of cell proliferation. 3. Independent of this population density effect, RIE-1 cells also exhibit a marked phenotypic transition around passage-8 to -10, such that later-passage cells were less responsive to growth inhibition by TGF-beta 1.

A study of the thermal denaturation of ribonuclease S by electrospray ionization mass spectrometry

The thermal stability of ribonuclease S (RNase S), an enzymatically active noncovalent complex composed of a 2166-u peptide (S-peptide) and a 11,534-u protein (S-protein), was investigated by electrospray ionization mass spectrometry (ESI-MS) and capillary electrophoresis ESI-MS (CE-ESI-MS). The intensities of peaks corresponding to the RNase S complex were inversely related to both the applied nozzle-skimmer (or capillary-skimmer) voltage bias in the atmosphere-vacuum interface and the temperature of the RNase S solution. By using a heated metal capillary-skimmer interface and a room temperature solution of RNase S, the intensities of RNase S molecular ion peaks were observed to decrease with increasing metal capillary temperature. Mass spectrometric studies with both the nozzle-skimmer and capillary-skimmer interface designs allowed determination of phenomenological enthalpies for dissociation of the RNase S complex in both solution and for the electrosprayed microdroplet-gas phase species. Intact RNase S complex could also be detected with CE-ESI-MS separations by using a 10-mM ammonium bicarbonate (pH 7.9) solution as the electrophoretic buffer. These studies provide new insights into the stability of multiply charged noncovalent complexes in the gas phase and the mass spectrometric conditions required for such studies, and suggest that information regarding solution properties can be obtained by ESI-MS.

Comparison of the responses of three rat intestinal epithelial cell lines to angiotensin II

Like RIE-1 cells, two of the IEC series of rat intestinal epithelial cell lines were found to express functional angiotensin receptors. As in RIE-1 cells, treatment of IEC-6 or IEC-18 cells with angiotensin II (AII) activated phosphatidylinositol-4,5-bisphosphate (PIP2) hydrolysis although (in contrast to RIE-1 cells) the magnitude of AII-induced PIP2 hydrolysis was small and not associated with a mitogenic response in either IEC cell line. In terms of their other functional responses to AII (activation of protein kinase C (PKC) and a small elevation of cyclic AMP), IEC-6 cells are otherwise similar to RIE-1 cells whereas IEC-18 cells exhibit some phenotypic differences to the other two cell types. Thus, whereas IEC-6 and RIE-1 cells each express the AT1 subtype of angiotensin receptor, the higher affinity receptors on IEC-18 cells are 'atypical', being insensitive to both AT1- and AT2-specific angiotensin receptor antagonists. Furthermore, in contrast to its effects in IEC-6 and RIE-1 cells, AII neither activates PKC nor modulates cyclic AMP levels in IEC-18 cells. Whereas IEC-18 cells express the myristoylated alanine-rich C-kinase substrate (MARCKS), immunoreactive MARCKS was not detected in IEC-6 or RIE-1 cells.

Investigation of the gas-phase structure of electrosprayed proteins using ion-molecule reactions

Proton transfer reactions of ammonia, dimemylamine, diethylamine, and trimethylarnine with multiply protonated proteins generated by electrospray ionization (ESI) were examined to probe the relationship between solution and gas-phase protein structure and the relationship with ion-molecule reactivity. The ion-molecule reactions were carried out in an atmospheric pressure capillary inlet/reactor based upon an ESI interface to a quadrupole mass spectrometer. Two types of systems were explored: (1) proteins possessing cysteine-cysteine disulfide bonds and the analogous disulfide-reduced proteins, and (2) proteins sprayed from solution compositions where the protein has different conformations. While the cysteine-cysteine disulfide-bound proteins were more reactive than equally charged disulfide-reduced proteins under these conditions, no significant reactivity differences were noted for ions arising from different solution conformations. The effect of inlet/reactor temperature on charge distributions with and without amine reagent was also explored, demonstrating that thermal denaturation of proteins can occur in heated capillary inlets. The results are discussed in the context of recent results indicating the persistence of at least some higher order protein structure in the gas phase.

Characterisation of AT1 angiotensin receptors on cultured rat intestinal epithelial (RIE-1) cells

The relative binding affinities of non-peptide antagonists, and the sensitivity of 125I-angiotensin II (125I-AII) binding to the reducing agent, dithiothreitol, indicated the presence of AT1 angiotensin receptors on RIE-1 rat intestinal epithelial cells. Consistent with this finding, AT1 angiotensin receptor mRNA was detected in RIE-1 cells using Northern blotting, whereas no mas transcripts (which also encode an angiotensin receptor) were detectable using a RNAse protection assay. At 37 degrees C, 125I-AII rapidly bound to RIE-1 cells and internalised into an acid-inaccessible compartment, which resulted in the depletion of 125I-AII from the binding medium. Following overnight incubation of RIE-1 cells with 125I-AII at 4 degrees C, the majority of bound ligand was also, unexpectedly, found to be inaccessible to subsequent acid elution. After warming these cultures to 37 degrees C, acid-inaccessible 125I-radioactivity rapidly disappeared from the cells, and 125I-labelled degradation products accumulated in the medium. Scatchard analysis of the concentration-dependent binding of 125I-AII solely to the acid-accessible sites on RIE-1 cells revealed little difference to the KD value obtained from total 125I-AII binding (to both acid-accessible and -inaccessible sites), but only approximately 15% of the number of sites.

Observation of noncovalent complexes to the avidin tetramer by electrospray ionization mass spectrometry

Intact avidin-biotin and avidin-biotin maleimide noncovalent complexes have been observed by electrospray ionization mass spectrometry (ESI-MS) by using an extended mass range quadrupole mass spectrometer. By utilizing mild ES1 interface conditions, the expected solution behavior of four biotin or biotin maleimide molecules noncovalently binding to each avidin tetramer can be preserved in the gas phase. The ESI-MS results show the appropriate mass additions of 973 ± 60 Da for biotin and 1802 ± 40 Da for biotin maleimide to the avidin tetramer species. These results support the hypothesis that substantial retention of higher order structure is possible in the gas phase by using gentle ESI conditions.

Regulation of growth factor receptors on rat intestinal epithelial (RIE-1) cells by protein kinase C

The regulation of growth factor receptors by protein kinase C was investigated in rat intestinal epithelial (RIE-1) cells. Short-term treatment of the cells with the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate, was employed to activate the kinase and longer-term exposure to the agent was used to assess the effects of protein kinase C depletion. Phorbol ester concentrations as low as 30 nM were found to down-regulate immunoreactive protein kinase C over 6 h, which correlated with the rapid loss of functional kinase activity. Whereas protein kinase C reduced the binding of 125I-labelled EGF, it increased the binding of 125I-labelled angiotensin II to RIE-1 cells. However, the kinase simultaneously inhibited the activation by angiotensin receptors of phosphatidylinositol 4,5 bisphosphate hydrolysis.

Sheathless capillary electrophoresis-electrospray ionization mass spectrometry using 10 mu m I.D. capillaries: analyses of tryptic digests of cytochrome c

The analyses of tryptic digest of proteins present a difficult challenge to the analytical chemist due to the wide range of molecular masses and hydrophobicities of the peptides produced. In this study, we demonstrate the separation of tryptic digests of bovine, Candida krusei and equine cytochrome c using a new electrospray ionization (ESI) interface for CE-MS that does not require additional sheath make-up fluid or mechanical assistance to aid the ESI process. The utility of this new CE-ESI-MS interface is demonstrated using a 10 microm I.D. CE capillary where the injected sample amounts are in the 30 femtomole (of protein) region. The CE electroosmotic flow rates when aminopropylamine treated capillaries are utilized are in the 10 nl/min region for a relatively conductive buffer system (0.01 M ammonium acetate-acetic acid buffer system, pH 4.4 and a 300 V/cm field strength).

Human angiotensin receptor subtypes

The rapid expansion of our knowledge of angiotensin receptors has been led by the development of subtype-specific angiotensin II receptor antagonists and by the cloning and sequencing of the AT1 receptor in angiotensin II. Although some actions of angiotensin II have been attributed to AT2 subtype receptors, the importance of these binding sites remains elusive. Nonpeptide, AT1-selective antagonists, such as losartan, block virtually all of the well-known effects of angiotensin II in mammalian cells. The effects of losartan are now being confirmed by the rapidly developing class of nonpeptide, AT1-selective angiotensin II receptor antagonists. In rodents, subtypes of the AT1 receptor have been cloned and designated AT1A and AT1B, but they have not been functionally distinguished. Such isoforms have not been identified for human AT1 receptors. Importantly, it now appears that the AT2 receptor has been cloned. The angiotensin receptors undergoing intense study are those in fetal tissue, brain, endothelial cells, and fibroblasts. Angiotensin II-induced growth and cardiovascular hypertrophy are the focus of broad-based research efforts. The clinical relevance of angiotensin II receptor subtypes is unknown, but there is growing evidence that AT1-selective agents are effective inhibitors of the angiotensin system in humans.

Identification of AT2 angiotensin receptors on Swiss 3T3 cells

Swiss 3T3 cells express high-affinity receptors for angiotensin II (KD = 0.8 nM, 110,000 receptors/cell). Binding of the peptide to these receptors did not activate phosphatidylinositol 4,5 bisphosphate hydrolysis, and did not increase intracellular [Ca2+] or activate protein kinase C. The relative binding affinities of highly-selective antagonists characterised these receptors as the AT2 subtype. However, in contrast to the signalling events reported in some other cells that express AT2 receptors, AII had no apparent effect on either cyclic GMP levels or phosphotyrosine phosphatase activity in Swiss 3T3 cells. Furthermore, angiotensin II (either alone or in combination with growth factors) was not mitogenic to Swiss 3T3 cells.

SURVEY REPORT on Forensic Nursing

1. There are at least 1,200 registered nurses working in psychiatric forensic facilities, 5% of whom are master's prepared. In 1991, approximately 1,900 student nurses were affiliated with an institution providing evaluation and treatment for mentally ill offenders. 2. Based on the response to this survey, there is an eagerness to develop a professional network of forensic psychiatric nurses. The nature of this practice tends to be isolating, with heretofore infrequent opportunities to share common concerns and challenges. 3. Forensic psychiatric nurses represent a stable work force of substantial tenure. The most rewarding aspects of forensic nursing identified by the survey were the potential for autonomous professional practice and the unique challenges of providing care in a security environment.

Decision analysis in the evaluation of diagnostic tests

Decision analysis was used to evaluate the clinical usefulness of 2 diagnostic tests: one for canine heartworm disease and the other for bovine traumatic reticulo-peritonitis. Several clinically relevant measures of test performance are introduced, including expected utility, risk profile, testing band, threshold analysis, and the relative cost of misdiagnosis. One of the principal benefits of decision analysis of diagnostic tests is that the technique can be used to determine how changes in underlying assumptions will affect clinical decisions. If clinicians can identify and assign values to relevant variables, then decision analysis can provide clinically meaningful guidelines for interpreting the results of diagnostic tests. To take advantage of these techniques, clinicians must become comfortable with quantitative expressions for test performance, risk, and prognosis.

New developments in microscale separations and mass spectrometry for biomonitoring: capillary electrophoresis and electrospray ionization mass spectrometry

In this article, we briefly highlight the use of capillary electrophoresis for sampling, manipulating, and separating extremely small sample sizes. The extraordinary sensitivity that can be obtained by combined capillary electrophoresis-mass spectrometry is then demonstrated using recent results. We briefly describe the ability to detect noncovalently associated complexes (e.g., double-stranded DNA) by electrospray ionization-mass spectrometry, and conclude with recent results that show the potential for using high-resolution Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry for characterization of biomolecules.

National pathology manpower survey of 1991. Projected needs in community hospitals and private laboratory practice

The third survey of a representative group of pathologists in community practice confirms the prediction based on the 1987 and 1988 surveys that there would be a growing deficit in the number of pathologists in this practice setting. There is an increasing number of reported vacancies in pathology groups and a significant increment in the percentage of older pathologists, with 32% being older than 54 years of age in 1991, compared with 25% in 1987. Projections based on the plan of individual respondents to retire and the anticipated changes in practice groups suggest that there will continue to be more pathologists leaving practice than new pathologists entering the specialty.

New perspectives in angiotensin system control

The 'angiotensin system' is expressed at the whole body, organ/tissue and cellular levels through the action of angiotensin II at specific receptors. An appreciation of the full scope of the actions of angiotensin II (endocrine, paracrine and autocrine) has been made possible by the discovery of the non-peptide angiotensin II receptor antagonists, losartan (DuP 753/MK954)(AT1-selective) and PD123177 (AT2-selective). Virtually all of the known effects of angiotensin II are blocked by losartan and designated AT1. Selective AT1 receptor blockade with losartan lowers BP in angiotensin II-dependent models of hypertension, reduces cardiac hypertrophy, improves haemodynamics in models of cardiac failure and reduces the intimal response to vascular injury. AT2 sites have been localised in distinct parts of the brain and in foetal tissue. The functional role of the AT2 sites remains controversial, but possible roles in neuronal ion channel function and collagen metabolism in fibroblasts have been reported. AT1 (losartan-sensitive) receptor subtypes have now been cloned from several rat tissues, suggesting that selective agents of the future may be even more specifically targeted. New perspectives in the control of the angiotensin system continue to evolve rapidly as the new receptor antagonists and molecular biology techniques expand our understanding of angiotensin II.

High-resolution accurate mass measurements of biomolecules using a new electrospray ionization ion cyclotron resonance mass spectrometer

A novel electrospray ionization/Fourier transform ion cyclotron resonance mass spectrometer based on a 7-T superconducting magnet was developed for high-resolution accurate mass measurements of large biomolecules. Ions formed at atmospheric pressure using electrospray ionization (ESI) were transmitted (through six differential pumping stages) to the trapped ion cell maintained below 10(-9) torr. The increased pumping speed attainable with cryopumping (> 10(5) L/s) allowed brief pressure excursions to above 10(-4) torr, with greatly enhanced trapping efficiencies and subsequent short pumpdown times, facilitating high-resolution mass measurements. A set of electromechanical shutters were also used to minimize the effect of the directed molecular beam produced by the ES1 source and were open only during ion injection. Coupled with the use of the pulsed-valve gas inlet, the trapped ion cell was generally filled to the space charge limit within 100 ms. The use of 10-25 ms ion injection times allowed mass spectra to be obtained from 4 fmol of bovine insulin (Mr 5734) and ubiquitin (Mr 8565, with resolution sufficient to easily resolve the isotopic envelopes and determine the charge states. The microheterogeneity of the glycoprotein ribonuclease B was examined, giving a measured mass of 14,898.74 Da for the most abundant peak in the isotopic envelope of the normally glycosylated protein (i.e., with five mannose and two N-acetylglucosamine residues (an error of approximately 2 ppm) and an average error of approximately 1 ppm for the higher glycosylated and various H3PO4 adducted forms of the protein. Time-domain signals lasting in excess of 80 s were obtained for smaller proteins, producing, for example, a mass resolution of more than 700,000 for the 4(+) charge state (m/z 1434) of insulin.

Observation and implications of high mass-to-charge ratio ions from electrospray ionization mass spectrometry

High mass-to-charge ratio ions (> 4000) from electrospray ionization (ESI) have been observed for several proteins, including bovine cytochrome c (M r 12,231) and porcine pepsin (M r 34,584), by using a quadrupole mass spectrometer with an m/z 45,000 range. The ESI mass spectrum for cytochrome c in an aqueous solution gives a charge state distribution that ranges from 12 + to 2 +, with a broad, low-intensity peak in the mass-to-charge ratio region corresponding to the [M + H](+) ion. the negative ion ESI mass spectrum for pepsin in 1% acetic acid solution shows a charge state distribution ranging from 7- to 2-. To observe the [M - H](-) ion, harsher desolvation and interface conditions were required. Also observed was the abundant aggregation of the protens with average charge states substantially lower than observed for their monomeric counterparts. The negative ion ESI mass spectrum for cytochrome c in 1-100 mM NH4OAc solutions showed greater relative abundances for the higher mass-to-charge ratio ions than in acuidic solutions, with an [M - H](-) ion relative abundance approximately 50% that of the most abundant charge state peak. The observation that protein aggregates are formed with charge states comparable to monomeric species (at fower mass-to-charge ratios) suggests that the high mass-to-charge ratio monomers may be formed by the dissociation of aggregate species. The observation of low charge state and aggregate molecular ions concurrently with highly charged species may serve to support a variation of the charged residue model, originally described by Dole and co-workers (Dole, M., et al. J. Chem. Phys. 1968, 49, 2240; Mack, L. L., et al. J. Chem. Phys. 1970, 52, 4977) which involves the Coulombically driven formation of either very highly solvated molecular ions or lower ananometer-diameter droplets.

Predicting response to amitriptyline in posttraumatic stress disorder

OBJECTIVE

This study evaluated the relation between baseline clinical phenomena and response to amitriptyline in patients with posttraumatic stress disorder (PTSD).

METHOD

Data were obtained from an 8-week placebo-controlled, double-blind study of combat veterans. Bivariate and multivariate statistics were used to evaluate the relations between the following variables and outcome: age, depression, anxiety, severity of PTSD symptoms, personality, psychiatric comorbidity, level of exposure to trauma, and individual symptoms of depression, anxiety, and traumatic stress. Outcome measures were scores on the Clinical Global Impression scale, Hamilton Rating Scale for Depression, Hamilton Rating Scale for Anxiety, and Impact of Event Scale.

RESULTS

Drug response was related to lower baseline levels of depression, neuroticism, combat intensity, anxious mood, impaired concentration, somatic symptoms, feelings of guilt, and one intrusion and four avoidance symptoms of PTSD.

CONCLUSIONS

The results demonstrate that response to amitriptyline is related to measures of depression, anxiety, PTSD, personality, and intensity of combat trauma. Similar relationships were not observed in the placebo group, suggesting a specific relationship to the drug.