Deficient neurogenesis in forebrain-specific presenilin-1 knockout mice is associated with reduced clearance of hippocampal memory traces

To examine the in vivo function of presenilin-1 (PS1), we selectively deleted the PS1 gene in excitatory neurons of the adult mouse forebrain. These conditional knockout mice were viable and grew normally, but they exhibited a pronounced deficiency in enrichment-induced neurogenesis in the dentate gyrus. This reduction in neurogenesis did not result in appreciable learning deficits, indicating that addition of new neurons is not required for memory formation. However, our postlearning enrichment experiments lead us to postulate that adult dentate neurogenesis may play a role in the periodic clearance of outdated hippocampal memory traces after cortical memory consolidation, thereby ensuring that the hippocampus is continuously available to process new memories. A chronic, abnormal clearance process in the hippocampus may conceivably lead to memory disorders in the mammalian brain.

Differential effects of enrichment on learning and memory function in NR2B transgenic mice

It has been known that environmental enrichment leads to better learning and memory in mice. However, the molecular mechanisms are not known. In this study, we used the 10th-12th of the NR2B transgenic (Tg) lines, in which the NMDA receptor function is enhanced via the NR2B subunit transgene in neurons of the forebrain, to test the hypothesis of the involvement of NMDA receptor function in enrichment-induced better learning and memory. Consistent with our previous results, both larger long-term potentiation (LTP) in the hippocampus and superior learning and memory were observed in naive NR2B Tg mice even after the 10th-12th generation of breeding. After enrichment, wild-type mice exhibited overall improvement in their performances in contextual and cued conditioning, fear extinctions, and novel object recognition tasks. Interestingly, the same enrichment procedures could not further increase the performance of NR2B Tg mice in contextual conditioning, cued conditioning, or fear extinction, thereby indicating that enhanced NMDA receptor function can occlude these enrichment effects. However, we found that in the novel object recognition task enriched NR2B Tg mice exhibited much longer recognition memory (up to 1 week), compared to that (up to 3 days) in naive NR2B Tg mice. Furthermore, our biochemical experiments showed that enrichment significantly increased protein levels of GluR1, NR2B, and NR2A subunits of glutamate receptors in both wild-type and NR2B Tg mice. Therefore, our results suggest an interactive nature of molecular pathways involved in both environmental and genetic NMDA receptor manipulations for enhancing learning and memory.

Electronic structure of epitaxial graphene layers on SiC: effect of the substrate

A strong substrate-graphite bond is found in the first all-carbon layer by density functional theory calculations and x-ray diffraction for few graphene layers grown epitaxially on SiC. This first layer is devoid of graphene electronic properties and acts as a buffer layer. The graphene nature of the film is recovered by the second carbon layer grown on both the (0001) and (0001[over]) 4H-SiC surfaces. We also present evidence of a charge transfer that depends on the interface geometry. Hence the graphene is doped and a gap opens at the Dirac point after three Bernal stacked carbon layers are formed.

Transmutation of a heme protein

Residue Asn57 of bovine liver cytochrome b5 has been replaced with a cysteine residue, and the resulting variant has been isolated from recombinant Escherichia coli as a mixture of four major species: A, BI, BII, and C. A combination of electronic spectroscopy, 1H NMR spectroscopy, resonance Raman spectroscopy, electrospray mass spectrometry, and direct electrochemistry has been used to characterize these four major cytochrome derivatives. The red form A (E(m) = -19 mV) is found to possess a heme group bound covalently through a thioether linkage involving Cys57 and the alpha carbon of the heme 4-vinyl group. Form BI has a covalently bound heme group coupled through a thioether linkage involving the beta carbon of the heme 4-vinyl group. Form BII is similar to BI except that the sulfur involved in the thioether linkage is oxidized to a sulfoxide. The green form C (E(m) = 175 mV) possesses a noncovalently bound prosthetic group with spectroscopic properties characteristic of a chlorin. A mechanism is proposed for the generation of these derivatives, and the implications of these observations for the biosynthesis of cytochrome c and naturally occurring chlorin prosthetic groups are discussed.

Analysis of antibodies and other large glycoproteins in the mass range of 150,000-200,000 Da by electrospray ionization mass spectrometry

The analytical applicability of electrospray ionization mass spectrometry (ESIMS) to large glycoproteins in the molecular weight (MW) range of 150,000-200,000 was demonstrated. Multiply charged ions (charge state as high as 150+) of several typical macrosized glycoproteins of immunological significance were generated by pneumatically-assisted electrospray (ionspray) and their masses measured on a quadrupole mass spectrometer having a mass-to-charge (m/z) range of 2400. The resolution of the quadrupole instrument was insufficient to resolve the glycocomposition microheterogeneities in the MW range studied. Nevertheless, the average MWs of three immunoglobulin G (IgG) class murine monoclonal antibodies, anti-(human alpha 1-antitrypsin) (148,484 +/- 4), anti-(human alpha 1-acid glycoprotein) (149,599 +/- 12) and anti-(beta-galactosidase) (component I, 150,544 +/- 10, and component II, 151,496 +/- 17), and human alpha 2-macroglobulin monomer (186,100 +/- 100), and human complement component C4 (196,863 +/- 29) were still determined from the fused peak profiles of their constituent glyco components (the errors given reflect the measurement precisions of the simultaneous multichannel MW determinations). The difference between the measured average MW and the unmodified sequence MW was used to assess the degree of post-transitional modification in human alpha 2-macroglobulin (13.6%) and human complement component C4 (5.3%). For the large glycoproteins studied here, glycosylation did not appear to seriously affect the effectiveness of the electrospray ionization; up to 70% of their full charge-retaining capacities were fulfilled under the usual experimental conditions. These results show that ESIMS is capable of providing analytically useful information for macrosized proteins.

Watermarking medical signals for telemedicine

Modern telecommunication infrastructure supports the possibility of delivering quality health care without the physical presence of medical experts. The integrity of biomedical signals being transmitted through communication channels must be established before their utilization. This paper investigates three digital watermarking techniques for signal integrity verification in an electroencephalogram (EEG) monitoring application for brain injury detection. The techniques studied are patchwork, least significant bit, and quantization watermarking methods. The three techniques are evaluated and compared in the following areas: sensitivity to noise contamination, robustness to EEG signal characteristic changes due to brain injury, and consistency under various communication channel models. The patchwork method performs best for noise contamination rejection among the three methods. The noise contamination detection rates of all three methods remain relatively stable across a wide range of EEG characteristics.

Stepwise refolding of Acid-denatured myoglobin: Evidence from electrospray mass spectrometry

Application of electrospray mass spectrometry (ES/MS) to a protein refolding study was demonstrated. Acid denaturation of equine myoglobin was reversed by adding various amounts of ammonium hydroxide to the protein that was unfolded in 10% acetic acid. The protein refolding process was followed by ES/MS, in which both the changes in the protein charge-state distribution and mass were monitored. The ES/MS results show that the pH-dependent renaturation of the acid-denatured myoglobin is stepwise, consisting of two major steps. The unfolded polypeptide chain first refolds to establish a compact nativelike structure, without the assistance of the heme prosthetic group. The newly formed binding cavity then retains the heme group by noncovalent interactions. It is also shown that inclusion of a stabilizing buffer, such as ammonium acetate, in the protein solution is greatly beneficial to the ES/MS detection of intact noncovalent globin/heme complex.

High Accuracy Molecular Weight Determination and Variation Characterization of Proteins Up To 80 ku by Ionspray Mass Spectrometry

A quadrupole mass spectrometer with an ionspray interface was used to measure the molecular weight (MW) of proteins up to 80,000 u . With the improvements in instrument cahbration by a statistical averaging method and in data analysis by a gaussian curve-fitting method, precision of MW determination as high as 12 ppm was achieved with equine myoglobin (MW 16,950.4 ± 0.2 u). Exact MW determination of three components in cerato-ulmin revealed that the two minor ones had lost amino acid residues Ser and Ser-Asp, respectively, from the major component (MW 7618.4 ± 0.2 u). MW classifIcation of eight components in the Fab fragment of a monoclonal antibody revealed that one set of four had MW - 47,540 u and the other - 47,640 u. The MW difference of 100.2 ± 0.6 u between fragment 1 and 2, attributed to inhomogeneous cleavage at the Fab C-terminus, was probably due to one additional Thr in 1. The MW of bovine serum albumin (BSA) was found to be 66,431.5 ± 1.3 u, - 164 u higher than the calculated sequence MW, most probably because of the incorrectness in the previously reported BSA amino acid sequence. The MW of human serum transferrin (79,556.8 ± 1.7 u) was shown to be 4414 u higher than the sequence MW, pointing to a glycosylation of 22.7 sugar units in this protein. The greater complexity in bovine serum transferrin (MW 78,030.5 ± 1.8 and 78,326 ± 3.3 u for the two major components) was correlated with the heterogeneity in the glycosylation.

Helicobacter pylori-induced Sonic Hedgehog expression is regulated by NFκB pathway activation: the use of a novel in vitro model to study epithelial response to infection

BACKGROUND

Helicobacter pylori (H. pylori) infection leads to acute induction of Sonic Hedgehog (Shh) in the stomach that is associated with the initiation of gastritis. The mechanism by which H. pylori induces Shh is unknown. Shh is a target gene of transcription factor Nuclear Factor-κB (NFκB). We hypothesize that NFκB mediates H. pylori-induced Shh.

MATERIALS AND METHODS

To visualize Shh ligand expression in response to H. pylori infection in vivo, we used a mouse model that expresses Shh fused to green fluorescent protein (Shh::GFP mice) in place of wild-type Shh. In vitro, changes in Shh expression were measured in response to H. pylori infection using 3-dimensional epithelial cell cultures grown from whole dissociated gastric glands (organoids). Organoids were generated from stomachs collected from the fundic region of control and mice expressing a parietal cell-specific deletion of Shh (PC-Shh(KO) mice).

RESULTS

Within 2 days of infection, H. pylori induced Shh expression within parietal cells of Shh::GFP mice. Organoids expressed all major gastric cell markers, including parietal cell marker H(+) ,K(+) -ATPase and Shh. H. pylori infection of gastric organoids induced Shh expression; a response that was blocked by inhibiting NFκB signaling and correlated with IκB degradation. H. pylori infection of PC-Shh(KO) mouse-derived organoids did not result in the induction of Shh expression.

CONCLUSION

Gastric organoids allow for the study of the interaction between H. pylori and the differentiated gastric epithelium independent of the host immune response. H. pylori induces Shh expression from the parietal cells, a response mediated via activation of NFκB signaling.

The TNF-α, IL-1B and IL-10 polymorphisms and risk for hepatocellular carcinoma: a meta-analysis

OBJECTIVE

TNF-α-308 G/A, TNF-α-238 G/A, IL-1B-31 T/C, IL-1B-511 C/T, and IL-10-1082 G/A polymorphisms have been reported to influence the risk for hepatocellular carcinoma (HCC) in many studies; however, the results still remains controversial and ambiguous. The aim of this study was to determine more precise estimations for the relationship between TNF-α, IL-1B, and IL-10 polymorphisms and the risk for HCC by meta-analysis.

METHODS

Electronic searches for all publications were conducted on associations between these variants and HCC in several databases through September 2010. Odds ratios (OR) with 95% confidence intervals (95% CI) were calculated to estimate the strength of this association in a random-effect model. Twenty studies were identified, involving 2,763 HCC patients and 4,152 controls.

RESULTS

This meta-analysis showed significant association between TNF-α-308 polymorphism and HCC (AA + GA vs. GG: OR = 1.74, 95% CI = 1.12-2.72). In Caucasian and Asian subgroups, OR values (95% CI) were 1.49 (0.58-3.82) and 1.84 (1.06-3.20), respectively. While the ORs for TNF-α-238 G/A, IL-1B-31 T/C, -511 C/T and IL-10-1082 G/A polymorphisms and HCC were 1.37 (0.95-2.00), 1.24 (0.99-1.55), 1.12 (0.66-1.88) and 0.91 (0.74-1.12), respectively. The sensitivity analysis further strengthened the overall strong positive correlations. No publication bias was observed in this study.

CONCLUSIONS

TNF-α-308 G/A polymorphism is assumed to confer a higher risk for HCC, especially in Asian population. TNF-α-238 G/A, IL-1B-31 T/C, -511 C/T, and IL-10-1082 G/A polymorphisms were not detected to be related to the risk for HCC.

CD34+/CD41a+ cells best predict platelet recovery after autologous peripheral blood stem cell transplantation

Reliable markers for megakaryocytic reconstitution after peripheral blood stem cell transplantation (PBSCT) have not been established. To determine a convenient and reliable predictor, we measured the number of megakaryocyte progenitor cells in PBSC grafts by clonogenic and flow cytometric assays. Seventeen patients with hematological and solid malignancies were included in this study. For the clonogenic assay, we used thrombopoietin (TPO) as a growth factor to evaluate the maximum number of megakaryocyte progenitor cells. Using a flow cytometric assay, we examined the expression of platelet glycoproteins on CD34+ cells to count the number of megakaryocyte progenitor cells. We used buffer containing EDTA to prevent platelet adhesion to CD34+ cells and selected CD34+ cells by immunomagnetic beads. The best correlation was observed between the number of CD34+/CD41a+ cells and the time to platelet recovery (P = 0.0205), rather than the total number of CD34+ cells. In addition, a close correlation was observed between the number of CD34+/CD41a+ cells and colony-forming unit megakaryocyte (CFU-MK) (P = 0.0018). These observations suggest that the number of CD34+/CD41a+ cells is the best predictor for platelet reconstitution after PBSCT.

Genetic and environmental contributions to body mass index: comparative analysis of monozygotic twins, dizygotic twins and same-age unrelated siblings

BACKGROUND

Earlier studies have established that a substantial percentage of variance in obesity-related phenotypes is explained by genetic components. However, only one study has used both virtual twins (VTs) and biological twins and was able to simultaneously estimate additive genetic, non-additive genetic, shared environmental and unshared environmental components in body mass index (BMI). Our current goal was to re-estimate four components of variance in BMI, applying a more rigorous model to biological and virtual multiples with additional data. Virtual multiples share the same family environment, offering unique opportunities to estimate common environmental influence on phenotypes that cannot be separated from the non-additive genetic component using only biological multiples.

METHODS

Data included 929 individuals from 164 monozygotic twin pairs, 156 dizygotic twin pairs, five triplet sets, one quadruplet set, 128 VT pairs, two virtual triplet sets and two virtual quadruplet sets. Virtual multiples consist of one biological child (or twins or triplets) plus one same-aged adoptee who are all raised together since infancy. We estimated the additive genetic, non-additive genetic, shared environmental and unshared random components in BMI using a linear mixed model. The analysis was adjusted for age, age(2), age(3), height, height(2), height(3), gender and race.

RESULTS

Both non-additive genetic and common environmental contributions were significant in our model (P-values<0.0001). No significant additive genetic contribution was found. In all, 63.6% (95% confidence interval (CI) 51.8-75.3%) of the total variance of BMI was explained by a non-additive genetic component, 25.7% (95% CI 13.8-37.5%) by a common environmental component and the remaining 10.7% by an unshared component.

CONCLUSION

Our results suggest that genetic components play an essential role in BMI and that common environmental factors such as diet or exercise also affect BMI. This conclusion is consistent with our earlier study using a smaller sample and shows the utility of virtual multiples for separating non-additive genetic variance from common environmental variance.

Detection of covalent enzyme-substrate complexes of nitrilase by ion-spray mass spectroscopy

Nitrilase from Rhodococcus ATCC 39484 was found to consist of two species of Mr 40,258 +/- 2 and 40,388 +/- 2 Da. When the enzyme was incubated with nitrile substrates and the reaction quenched with acid, higher Mr species were observed. The mass differences were consistent with addition of a substrate molecule to each species. These results represent the first reported demonstration that this, or any other nitrilase forms a covalent intermediate with its substrates. The observation that the intermediate, suggested to be either a thioimidate or an acylenzyme, can be trapped by acidification indicates that the rate of breakdown of the intermediate is rate-limiting.

A new murine oxidative stress model associated with senescence

A murine oxidative stress model was established via ozone inhalation, which was identified by detection of the response of antioxidant defense system, levels of oxidative products and effects of natural antioxidants on this model. Male BALB/c mice were exposed to 1.2 mg/m(3) ozone for 10 h per day. The control group was exposed to flowing air. From inhaling ozone, mice were killed at day 5, 10, 15 and 20, respectively. Exposure to ozone made mice show the increase of malondialdehyde (MDA) contents in heart, kidney and liver, as well as 8-OHdG levels in urine, and resulted in cytological nuclear concentration in brain neurons or thymocytes. Ozone exposure also impaired antioxidative capacity such as the decrease of total antioxidation capacity (TAC) in sera, reduced glutathione (GSH) in sera or thymus and glutathione-S-transferase (GST) activity in spleen or thymus but not in liver. Correlation analysis showed the significant inverse correlation (r=-0.894, P<0.05) between thymus weight index and inhalation doses of ozone. Meanwhile, thymocyte in model mice proliferated more poorly than normal controls. Catechin and clove extract could reverse parts of changes above induced by ozone inhalation. These results suggest that exposure to ozone can result in an increased production of reactive oxygen species in vivo, which causes oxidative stress. The mice under oxidative stress showed senescence-related alterations in physiological parameters as well. Taken together, our data demonstrates that an oxidative stress model in mice has been successfully established by ozone inhalation, which would be helpful to probe the relationship between oxidative stress and senescence and evaluate effects of antioxidants.

Conformational stability of heme proteins in vacuo

The function and conformational stability of myoglobin were studied in vacuo by using an electrospray mass spectrometer. The electrospray technique gently transfers protein molecules from the solution phase to the gas phase, and solvent-free protein ions are produced in the mass spectrometer. Horse myoglobin was dissolved at neutral pH, Fe3+ in the heme was reduced to Fe2+ to produce the biologically active oxymyoglobin in solution, and then the protein was isolated in vacuo. A molecular ion (17,601 Da) corresponding to the molecular mass of oxymyoglobin (17,600.0 Da) was observed in the mass spectrum. This demonstrates that the protein retains a heme and an oxygen molecule in the gas phase. Since the biological function of myoglobin is to carry an oxygen molecule, this is the first observation that a protein is functional in the absence of solvent. Gas-phase "unfolding" of myoglobin was also studied. Collisions of accelerated protein ions with nitrogen curtain gas at a quadrupole guidance lens or argon gas introduced at a second quadrupole increase the "molecular temperature" of myoglobin, resulting in release of the heme from myoglobin. Apomyoglobin produced at the quadrupole guidance lens showed a larger collisional cross section than that of myoglobin, revealing conformational disordering of the protein. The gas-phase unfolding of horse and whale myoglobins and the alpha-chain of human hemoglobin induced at the second quadrupole were studied as a function of the argon gas thickness. Horse and whale myoglobins showed the same gas-phase stability, whereas the alpha-chain of human hemoglobin was less stable.(ABSTRACT TRUNCATED AT 250 WORDS)

Electronic structure of epitaxial graphene layers on SiC: effect of the substrate

A strong substrate-graphite bond is found in the first all-carbon layer by density functional theory calculations and x-ray diffraction for few graphene layers grown epitaxially on SiC. This first layer is devoid of graphene electronic properties and acts as a buffer layer. The graphene nature of the film is recovered by the second carbon layer grown on both the (0001) and (0001[over]) 4H-SiC surfaces. We also present evidence of a charge transfer that depends on the interface geometry. Hence the graphene is doped and a gap opens at the Dirac point after three Bernal stacked carbon layers are formed.

The systemic management of cutaneous dermatomyositis: Results of a stepwise strategy

Treatment of dermatomyositis (DM) is often achieved with a stepwise algorithm. However, the literature lacks quality evidence to support the use of this therapeutic strategy. The result of a stepwise therapeutic strategy in the management of skin-only DM is presented to better understand the clinical outcomes and allow for future studies. A cohort of 102 patients with DM, 41 of whom had skin-only disease, were seen between July 2009 and April 2013 at a referral-based connective tissue disease clinic. The Cutaneous Dermatomyositis Disease Area and Severity Index was used to prospectively assess disease severity and the outcomes in 41 adult patients with skin-only DM were analyzed. Of the 41 patients with skin-only DM, 23 patients (56.1%) received antimalarial medications alone and 18 patients (43.9%) received second- or third-line agents. Ten patients (24.4%) remained at the first level of the treatment algorithm and received only hydroxychloroquine. Prednisone was included in the treatment regimen for 11 patients with skin-only disease (26.8%). The results show that management of cutaneous DM often requires second-line agents because antimalarial medications alone are insufficient to treat most patients with skin-only disease.

The accumulation and subcellular distribution of arsenic and antimony in four fern plants

In the present study, Pteris cretica 'Albo-Lineata' (PC), Pteris fauriei (PF), Humata tyermanii Moore (HT), and Pteris ensiformis Burm (PE), were selected to explore additional plant materials for the phytoremediation of As and Sb co-contamination. To some extent, the addition of As and Sb enhanced the growth of HT, PE, and PF. Conversely, the addition of As and Sb negatively affected the growth of PC and was accompanied with the accumulation of high levels of As and Sb in the roots. The highest concentration of Sb was recorded as 6405 mg kg(-1) in the roots of PC, and that for As was 337 mg kg(-1) in the rhizome of PF. To some degree, As and Sb stimulated the uptake of each other in these ferns. Arsenic was mainly stored in the cytoplasmic supernatant (CS) fraction, followed by the cell wall (CW) fraction. In contrast, Sb was mainly found in the CW fraction and, to a lesser extent, in the CS fraction, suggesting that the cell wall and cytosol play different roles in As and Sb accumulation by fern plants. This study demonstrated that these fern plants show a good application potential in the phytoremediation of As and Sb co-contaminated environments.

CT characteristics of patients infected with 2019 novel coronavirus: association with clinical type

AIM

To summarise the features of chest computed tomography (CT) of a series of patients infected with 2019 novel coronavirus (2019-nCov) to speed up recognition and have a better understanding of COVID-19 disease.

MATERIALS AND METHODS

The clinical information and chest CT images of 93 patients infected with 2019-nCov from multiple centres were reviewed.

RESULTS

Of the 93 cases, abnormalities in 91 cases were located at the subpleural level, presenting with ground-glass opacity (GGO; n=69, 74.2%) and consolidation (n=56, 60.2%) in multiple lobes. Other CT features included vascular dilatation (n=83, 89.2%), interlobular septal thickening (n=29, 31.2%), bronchodilatation (n=44, 47.3%), the crazy-paving sign (n=34, 36.6%), the sieve-hole sign (n=12, 12.9%), pleural thickening (n=21, 22.6%), and pleural effusion (n=8, 8.6%). Multiple lobe involvement, including the presence of consolidation, the crazy-paving sign, interlobular septal thickening, pleural thickening and pleural effusion, was more common in critical patients with heavy/critical infection (p<0.05), whereas the presence of GGO, involvement of one or two lobes, and the halo sign were more common in patients with mild/common-type infections (p<0.05). Moreover, older age, higher body temperature, complaints of chest tightness and breathlessness, and lymphopenia was associated with heavy/critical infections.

CONCLUSION

The CT and clinical appearances of COVID-19 are variable and reflect the severity of COVID-19 to some extent.

Targeted damage effects of high intensity focused ultrasound (HIFU) on liver tissues of Guizhou Province miniswine

HIFU can pass through tissues and accurately damage target tissues inside organisms. This article reports on the oriented damage effects of HIFU upon miniswine internal and external liver tissues, and suggests a new conception of the 'biological focal field'. The results revealed that: (1) HIFU can be used to damage accurately liver tissues under the guide of a B-modal ultrasound device; (2) the scope of the injury is connected with sound intensity and irradiation time; and (3) the different layers of tissue through which the ultrasound has passed remain undamaged.

Study of noncovalent enzyme-inhibitor complexes and metal binding stoichiometry of matrilysin by electrospray ionization mass spectrometry

Electrospray ionization mass spectrometry (ESI-MS) was used to study the noncovalent metallo-enzyme-inhibitor complexes of matrilysin (a matrix metalloproteinase of mass 18,720 u) under gentle experimental conditions and to determine the metal ion association stoichiometries in both the free enzyme and the complexes. The metal association stoichiometries of the free matrilysin were found to be highly sensitive to solution pH changes. At pH 2.2 the enzyme existed as metal-free apo-matrilysin and was not capable of binding an inhibitor. At pH 4.5-7.0 the enzyme associated specifically with zinc and calcium cations and became active in inhibitor binding. Although the stoichiometries of the metal cofactors varied (zero to two zinc and/or calcium ions) in the free enzyme dependent on solution pH, the predominant form of the enzyme-inhibitor complexes in the pH range of 4.5-7.0, in contrast, always had the metal association stoichiometry of 2Zn + 2Ca, which was the same stoichiometry the most active free metallo-enzyme had at the optimal pH of 7. At the activity onset pH of 4.5 matrilysin existed mostly as apo-enzyme (but in a conformation different from the denatured one at pH 2.2) and bound to an inhibitor slowly (time constant ∼ 2.5 min) to form the noncovalent metallo-enzyme-inhibitor complex. Of the two inhibitors studied, the one with the higher solution binding constant also produced larger ion signals for the noncovalent complex in the solvent-free gas phase, which pointed to the feasibility of the use of ESI-MS for inhibitor screening studies.