Development of a portable and cost-effective femtosecond fibre laser synchronizable with synchrotron X-ray pulses.

This study introduces a compact, portable femtosecond fibre laser system designed for synchronization with SPring-8 synchrotron X-ray pulses in a uniform filling mode. Unlike traditional titanium-sapphire mode-locked lasers, which are fixed installations, our system utilizes fibre laser technology to provide a practical alternative for time-resolved spectroscopy, striking a balance between usability, portability and cost-efficiency. Comprehensive evaluations, including pulse characterization, timing jitter and frequency stability tests revealed a centre wavelength of 1600 nm, a pulse energy of 4.5 nJ, a pulse duration of 35 fs with a timing jitter of less than 9 ps, confirming the suitability of the system for time-resolved spectroscopic studies. This development enhances the feasibility of experiments that combine synchrotron X-rays and laser pulses, offering significant scientific contributions by enabling more flexible and diverse research applications.

[IS INHALED CORTICOSTEROID STEP-DOWN RECOMMENDED FOR ADULT ASTHMA PATIENTS HAVE BEEN WELL CONTROLLED OVER THE LONG TERM WITH MODERATE OR HIGH-DOSE INHALED CORTICOSTEROIDS?]

We conducted a systematic review to examine whether step-down of inhaled corticosteroid (ICS) is recommended for adult patients with asthma have been well controlled with moderate or high-dose inhaled corticosteroids for more than 12 weeks. Seven randomized controlled trials were included. ICS step-down did not increase asthma exacerbations requiring systemic steroid therapy and hospitalization. There was no effect on respiratory function, asthma control, or QOL. No significant differences were observed in serious adverse events or steroid-related adverse events, but the observation period was insufficient to assess long-term effects. Based on these results, we weakly recommend ICS step-down in adult patients with asthma have been well controlled with moderate or high-dose inhaled corticosteroids, but long-term asthma control and the incidence of steroid-related adverse events should be further investigated in the future.

Experimental Demonstration to Control the Pulse Length of Coherent Undulator Radiation by Chirped Microbunching.

In seeded free electron lasers (FELs), the temporal profile of FEL pulses usually reflects that of the seed pulse, and, thus, shorter FEL pulses are available with shorter seed pulses. In an extreme condition, however, this correlation is violated; the FEL pulse is stretched by the so-called slippage effect in undulators, when the seed pulse is ultimately short, e.g., few-cycles long. In a previous Letter, we have proposed a scheme to suppress the slippage effect and reduce the pulse length of FELs ultimately down to a single-cycle duration, which is based on "chirped microbunching," or an electron density modulation with a varying modulation period. Toward realization of FELs based on the proposed scheme, experiments have been carried out to demonstrate its fundamental mechanism in the NewSUBARU synchrotron radiation facility, using an ultrashort seed pulse with the pulse length shorter than five cycles. Experimental results of spectral and cross-correlation measurements have been found to be in reasonable agreement with the theoretical predictions, which strongly suggests the successful demonstration of the proposed scheme.

Comprehensive analyses of microRNA and mRNA expression in colorectal serrated lesions and colorectal cancer with a microsatellite instability phenotype.

MicroRNA (miRNA) expression is dysregulated in human tumors, thereby contributing to tumorigenesis through altered expression of mRNA. Thus, identification of the relationships between miRNAs and mRNAs is important for evaluating the molecular mechanisms of tumors. In addition, elucidation of the molecular features of serrated lesions is essential in colorectal tumorigenesis. Here, we examined the relationships of miRNA and mRNA expressed in serrated lesions, including 26 sessile serrated lesions (SSLs), 12 traditional serrated adenomas (TSAs), and 11 colorectal cancers (CRCs) with a microsatellite instability (MSI) phenotype using crypt isolation. We divided the samples into the first and second cohorts for validation. Array-based expression analyses were used to evaluate miRNAs and mRNAs with opposite expression patterns in isolated tumor glands. In addition, we validated the relationships of miRNA/mRNA pairs in the second cohort using real-time polymerase chain reaction. We found that the expression of miRNA-5787 was correlated with reciprocal expression of two mRNAs, that is, SRRM2 and POLR2J3, in SSL samples. In TSA samples, two pairs of miRNAs/mRNAs showing opposite expression patterns, that is, miRNA-182-5p/ETF1 and miRNA-200b-3p/MYB, were identified. Ultimately, three pairs of miRNAs/mRNAs with opposite expression patterns, including miRNA-222-3p/SLC26A3, miRNA-6753-3p/FABP1, and miRNA-222-3p/OLFM4, were retained in CRC with an MSI phenotype. Finally, we performed transfection with an miR-222-3p mimic to confirm the expression of SLC26A3 and OLFM4; the results showed that ectopic expression of miR-222-3p moderately suppressed OLFM4 and downregulated SLC26A3 to some extent. Overall, our results provided basic insights into the evaluation of colorectal tumorigenesis of serrated lesions and CRC with an MSI phenotype.

Clinicopathological and molecular analyses of hyperplastic lesions including microvesicular variant and goblet cell rich variant hyperplastic polyps and hyperplastic nodules-Hyperplastic nodule is an independent histological entity.

Hyperplastic nodules (HNs) have been considered to be hyperplastic lesions among Japanese pathologists, although they have not been recognized worldwide. Here, we examined clinicopathological and molecular differences between goblet cell-rich variant hyperplastic polyp (GCHPs), microvesicular variant HPs (MVHPs), and HNs. Patients with hyperplastic lesions including 61 GCHPs, 62 MVHPs, and 19 HNs were enrolled in the present study. The clinicopathological and molecular features examined included the mucin phenotype expression, p53 overexpression, annexin A10, genetic mutations (BRAF and KRAS), and DNA methylation status (low, intermediate, and high methylation epigenotype). In addition, hierarchical cluster analysis was also performed to identify patterns among the histological features. The lesions were stratified into three subgroups and each lesion was assigned into a subgroup. While GCHP was associated with KRAS mutation, MVHP was closely associated with BRAF mutation; no mutation was found in HN. We list specific histological findings that corresponded to each lesion. Finally, there were no significant differences in the methylation status among lesions. The current result shows that both MVHPs and GCHPs have a neoplastic nature whereas HN is non-neoplastic. We suggest that HNs should be distinguished from HPs, in particular GCHPs, in terms of pathological and genetic features.

A genome-wide study of the relationship between chromosomal abnormalities and gene expression in colorectal tumors.

The role of somatic copy number alterations (SCNAs) that occur in colorectal tumors is poorly understood. SCNAs are correlated with corresponding gene expression changes that may contribute to neoplastic progression. Thus, we examined SCNAs and the expression of messenger RNAs (mRNAs) located at corresponding loci in colorectal neoplasia, a progression model of human neoplasm. We used 42 colorectal neoplastic samples, including adenomas, intramucosal cancers (IMC) and invasive colorectal cancers (CRC) that were microsatellite stable (MSS) using a genome-wide SNP array and gene expression array (first cohort). In addition, validation analyses were examined (37 colorectal neoplasias). None of the mRNAs with a corresponding SCNA was found in the adenomas. However, three mRNAs, including ARFGEF2 at 20q13.13, N4BP2L2 at 13q13.1 and OLFM4 at 13q14.3 with a copy number (CN) gain at the corresponding locus were upregulated in IMCs of the first cohort. Moreover, upregulated expression of ARFGEF2 and OLFM4 was upregulated in the validation analysis. Finally, 28 mRNAs with gains of corresponding loci were pooled in invasive CRC of the first cohort. The mRNAs, including ACSS2 (20q11.22), DDX27 (20q13.13), MAPRE1 (20q11.21), OSBPL2 (20q11.22) and PHF20 (20q11.22-q11.23) with CN gains of the corresponding loci were identified in 28 mRNAs. Four of these mRNAs (DDX27, MAPRE1, OSBPL2 and PHF20) were upregulated in the invasive CRC in the validation analysis. We conclude that specific 13q and 22q CN gains with gene expression changes in the corresponding loci may play an important role in IMC cells' progression into invasive CRC.

Development of an undulator with a variable magnetic field profile.

An undulator generating a magnetic field whose longitudinal profile is arbitrarily varied has been developed, which is one of the key components in a number of proposed new concepts in free-electron lasers. The undulator is composed of magnet modules, each of which corresponds to a single undulator period, and is driven by a linear actuator to change the magnetic gap independently. To relax the requirement on the actuator, the mechanical load on each module due to magnetic force acting from opponent and adjacent modules is reduced by means of two kinds of spring systems. The performance of the constructed undulator has been successfully demonstrated by magnetic measurement and characterization of synchrotron radiation.

Microenvironmental markers are correlated with lymph node metastasis in invasive submucosal colorectal cancer.

AIMS: Recent studies have shown that the microenvironment can include cancer cells and cancer-associated fibroblasts (CAFs), and that both play important roles in the progression and metastasis of CRC. Here, we aimed to analyse the expression patterns of cancer cell- and CAF-related proteins in submucosal invasive colorectal cancer (SiCRC) and whether such markers are correlated with lymph node metastasis (LNM). METHODS AND RESULTS: Quantitative analysis was conducted for Ki-67, p53, ß-catenin and matrix metalloproteinase-7 (MMP7) to assess cancer cell markers. In addition, we examined CAF markers, including smooth muscle alpha-actin (α-SMA), CD10, podoplanin, fibroblast-specific protein 1 (FSP-1), platelet-derived growth factor receptor (PDGFR)-α, PDGFR-ß, adipocyte enhancer-binding protein 1 (AEBP1), fibroblast-associated protein 1 (FAP-1), zinc finger E-box binding homeobox 1 (ZEB1) and TWIST-related protein 1 (TWIST1). In both cases, we conducted digital pathology with Aperio software. We also examined the expression patterns of biomarkers using hierarchical cluster analysis. Two subgroups were established based on the expression patterns of cancer cell- and CAF- related markers, and the associations of these subgroups with clinicopathological variables. In multivariate analysis, subgroup 2, which was characterised by high expression of Ki-67, p53, FAP-1, platelet-derived growth factor receptor (PDGFR)-α, PDGFR-ß and TWIST1, was correlated with LNM (P < 0.01). Next, we examined the associations of individual biomarkers with LNM. Multivariate analysis showed that high expression levels of Ki-67 and FAP-1 were significantly associated with LNM (P < 0.05). CONCLUSIONS: Our findings showed that expression patterns of cancer cell- and CAF-related proteins may allow for stratification of patients into risk categories for LNM in SiCRC. In addition, Ki-67- and FAP-1-expressing microenvironmental cells might be helpful for identification of correlations with LNM in SiCRC.

A genome-wide analysis of the molecular alterations occurring in the adenomatous and carcinomatous components of the same tumor based on the adenoma-carcinoma sequence.

Identification of molecular alterations occurring in the adenomatous and carcinomatous components within the same tumor would greatly enhance understanding of the neoplastic progression of colorectal cancer. We examined somatic copy number alterations (SCNAs) and mRNA expression at the corresponding loci involved in the adenoma-carcinoma sequence in the isolated adenomatous and cancer glands of the same tumor in 15 cases of microsatellite-stable "carcinoma in adenoma," using genome-wide SNP and global gene expression arrays. Multiple copy-neutral loss of heterozygosity events were detected at 4q13.2, 15q15.1, and 14q24.3 in the adenomatous component and at 4q13.2, 15q15.1, and 14q24.3 in the carcinomatous component. There were significant differences in the copy number (CN) gain frequencies at 20q11.21-q13.33, 8q13.3, 8p23.1, and 8q21.2-q22.2 between the adenomatous and carcinomatous components. Finally, we found a high frequency of five genotypes involving CN gain with upregulated expression of the corresponding gene (RPS21, MIR3654, RSP20, SNORD54, or ASPH) in the carcinomatous component, whereas none of these genotypes were detected in the adenomatous component. This finding is interesting in that CN gain with upregulated gene expression may enhance gene function and play a crucial role in the progression of an adenoma into a carcinomatous lesion.

Dysregulation of microRNA expression during the progression of colorectal tumors.

MicroRNAs (miRNAs) are potential biomarkers of neoplastic lesions, but additional information on dysregulated miRNA expression during progression of the adenoma-adenocarcinoma sequence may be helpful to identify the role of miRNAs in this sequence. We examined the expression levels of 13 miRNAs (hsa-miRNA-19a-3p, hsa-miRNA-21-5p, hsa-miRNA-27a-3p, hsa-miRNA-27b-3p, hsa-miRNA-31-5p, hsa-miRNA-34b-3p, hsa-miRNA-125b-5p, hsa-miRNA-143-3p, miRNA-191-5p, hsa-miRNA-193b-3p, hsa-miRNA-195-5p, hsa-miRNA-206 and hsa-let-7a-5p) that are closely associated with colorectal carcinogenesis in 40 conventional adenomas (tubular and tubulovillous adenomas), 20 intramucosal carcinomas (IMCs) and 60 invasive colorectal cancers (iCRCs) using reverse-transcription polymerase chain reaction. These 120 tumors were divided into two cohorts, that is, cohort 1 (60 cases) and cohort 2 (for validation; 60 cases). We analyzed the expression levels of these miRNAs in the first step (adenoma→IMC) and second step IMC→iCRC) of the adenoma-carcinoma sequence in both cohorts. Although no significant differences in the expression of any of the 13 miRNAs were found between adenomas and IMCs consistently in both cohorts, the expression levels of hsa-miRNA-125b-5p, hsa-miRNA-143-3p, and hsa-miRNA-206 were significantly upregulated in iCRC in both cohorts compared with those in IMC. The current results suggest that certain miRNAs, including hsa-miRNA-125b-5p, hsa-miRNA-143-3p and hsa-miRNA-206, are candidate markers that play critical roles in the progression of IMC to iCRC.

Sessile serrated adenoma/polyp showed rapid malignant transformation in the final 13 months.

Based on the concept of the adenoma-carcinoma sequence, most colorectal cancers are considered to arise from conventional adenomas. However, recent studies suggested that a subset of colorectal cancers develop through the serrated neoplastic pathway. It has also been documented that serrated polyps can rapidly transform into invasive cancers even when they are small in size. We now describe a case of a sessile serrated adenoma/polyp which had been followed up for 4 years but eventually showed rapid transformation into an advanced cancer accompanied by a remarkable morphological change within only 13 months. Retrospective genetic and epigenetic analyses showed microsatellite instability, CpG island methylator phenotype-positive, and BRAF mutation in the lesion, suggesting the tumor had developed through the serrated neoplastic pathway. This case may provide valuable information about the natural history of sessile serrated adenoma/polyps which eventually progress to advanced cancers.

A statistical approach to correct X-ray response non-uniformity in microstrip detectors for high-accuracy and high-resolution total-scattering measurements.

An unbiased approach to correct X-ray response non-uniformity in microstrip detectors has been developed based on the statistical estimation that the scattering intensity at a fixed angle from an object is expected to be constant within the Poisson noise. Raw scattering data of SiO2 glass measured by a microstrip detector module was found to show an accuracy of 12σPN at an intensity of 106 photons, where σPN is the standard deviation according to the Poisson noise. The conventional flat-field calibration has failed in correcting the data, whereas the alternative approach used in this article successfully improved the accuracy from 12σPN to 2σPN. This approach was applied to total-scattering data measured by a gapless 15-modular detector system. The quality of the data is evaluated in terms of the Bragg reflections of Si powder, the diffuse scattering of SiO2 glass, and the atomic pair distribution function of TiO2 nanoparticles and Ni powder.

Discovery of a pyrazolo[1,5-a]pyrimidine derivative (MT-3014) as a highly selective PDE10A inhibitor via core structure transformation from the stilbene moiety.

We have developed a new class of PDE10A inhibitor, a pyrazolo[1,5-a]pyrimidine derivative MT-3014 (1). A previous compound introduced was deprioritized due to concerns for E/Z-isomerization and glutathione-adduct formation at the core stilbene structure. We discovered pyrazolo [1,5-a] pyrimidine as a new lead scaffold by structure-based drug design utilizing a co-crystal structure with PDE10A. The lead compound was optimized for in vitro activity, solubility, and selectivity against human ether-á-go-go related gene cardiac channel binding. We observed that MT-3014 shows excellent efficacy in rat conditioned avoidance response test and suitable pharmacokinetic properties in rats, especially high brain penetration.

Subtypes of the Type II Pit Pattern Reflect Distinct Molecular Subclasses in the Serrated Neoplastic Pathway.

BACKGROUND: Colorectal serrated lesions (SLs) are important premalignant lesions whose clinical and biological features are not fully understood. AIMS: We aimed to establish accurate colonoscopic diagnosis and treatment of SLs through evaluation of associations among the morphological, pathological, and molecular characteristics of SLs. METHODS: A total of 388 premalignant and 18 malignant colorectal lesions were studied. Using magnifying colonoscopy, microsurface structures were assessed based on Kudo's pit pattern classification system, and the Type II pit pattern was subcategorized into classical Type II, Type II-Open (Type II-O) and Type II-Long (Type II-L). BRAF/KRAS mutations and DNA methylation of CpG island methylator phenotype (CIMP) markers (MINT1, - 2, - 12, - 31, p16, and MLH1) were analyzed through pyrosequencing. RESULTS: Type II-O was tightly associated with sessile serrated adenoma/polyps (SSA/Ps) with BRAF mutation and CIMP-high. Most lesions with simple Type II or Type II-L were hyperplastic polyps, while mixtures of Type II or Type II-L plus more advanced pit patterns (III/IV) were characteristic of traditional serrated adenomas (TSAs). Type II-positive TSAs frequently exhibited BRAF mutation and CIMP-low, while Type II-L-positive TSAs were tightly associated with KRAS mutation and CIMP-low. Analysis of lesions containing both premalignant and cancerous components suggested Type II-L-positive TSAs may develop into KRAS-mutated/CIMP-low/microsatellite stable cancers, while Type II-O-positive SSA/Ps develop into BRAF-mutated/CIMP-high/microsatellite unstable cancers. CONCLUSIONS: These results suggest that Type II subtypes reflect distinct molecular subclasses in the serrated neoplasia pathway and that they could be useful hallmarks for identifying SLs at high risk of developing into CRC.

Discovery of 2-[(E)-2-(7-Fluoro-3-methylquinoxalin-2-yl)vinyl]-6-pyrrolidin-1-yl-N-(tetrahydro-2H-pyran-4-yl)pyrimidin-4-amine Hydrochloride as a Highly Selective PDE10A Inhibitor.

Phosphodiesterase (PDE) 10A is a dual hydrolase of cAMP and cGMP and highly expressed in striatal medium spiny neurons. Inhibition of PDE10A modulates the activity of medium spiny neurons (MSN) via the regulation of cAMP and cGMP. Signal control of MSN is considered associated with psychotic symptoms. Therefore PDE10A inhibitor is expected as a therapeutic method for psychosis disease such as schizophrenia. Avanafil (1) is a PDE5 inhibitor (treatment for erectile dysfunction) discovered by our company. We paid attention to the homology of PDE10A and PDE5 and took advantage of PDE5 inhibitor library to discover PDE10A inhibitors, and found a series of compounds that exhibit higher potency for PDE10A than PDE5. We transformed the afforded derivatives, which had weak inhibitory activity against PDE10A, and discovered stilbene as a PDE10A inhibitor. Brain penetration of this compound was improved by further conversion of N-containing heterocycles and their substituents. The afforded dimethylaminopyrimidine was effective for rat conditioned avoidance response (CAR) test; however, it did not exhibit good brain penetration. We performed in-depth optimization focusing on substituents of the quinoxaline ring, and produced 3-methyl-7-fluoro quinoxaline. This compound was the most effective in rat CAR test due to its strong PDE10A inhibitory activity and good pharmacokinetics.

A single-arm phase II study of nab-paclitaxel for patients with chemorefractory non-small cell lung cancer.

BACKGROUND: We aimed to evaluate the efficacy and safety of nab-paclitaxel in patients with refractory advanced non-small cell lung cancer who failed previous chemotherapy. METHODS: Patients were required to have an Eastern Cooperative Oncology Group performance status of 0-2 and adequate organ function. Patients received nab-paclitaxel, 100 mg/m2 i.v. on days 1, 8, and 15 every 4 weeks. The primary endpoint was the overall response rate. Secondary endpoints were the progression-free survival time, overall survival, and the toxicity profile. RESULTS: From July 2013 to July 2015, a total of 31 patients were enrolled. Fourteen patients received nab-paclitaxel as a second-line and 17 received it as an over third-line therapy. Each patient received a median of 5 treatment cycles (range, 1-11). The overall response rate was 19.3% (95% confidence interval, 9.1-36.2%) (complete response (n = 0), partial response (n = 6), stable disease (n = 17), and progressive disease (n = 8)). The median progression-free survival time was 4.5 months (95% confidence interval 3.5-6.3 months), median overall survival time was 15.7 months, and 1-year survival rate was 54.8%. Most common grade 3 or 4 non-hematological toxicities were elevated aspartate transaminase level (3.2%) and sensory neuropathy (9.6%). Neutropenia was the most common grade 3 or 4 adverse events (38.6%), and febrile neutropenia developed in 12.9% patients. No treatment-related deaths were observed in this study. CONCLUSION: Primary endpoint was met. Single agent nab-paclitaxel showed significant clinical efficacy and manageable toxicities for patients with chemorefractory advanced non-small cell lung cancer even if late line setting. TRIAL REGISTRATION: UMIN000011696 . The date of registration was July 11th, 2013.

Endoscopic and molecular characterization of colorectal sessile serrated adenoma/polyps with cytologic dysplasia.

BACKGROUND AND AIMS: Sessile serrated adenoma/polyps (SSA/Ps), which are precursor lesions of colorectal cancer (CRC) with BRAF mutation and the CpG island methylator phenotype (CIMP), develop cytologic dysplasia (CD) during the progression of colorectal tumorigenesis. In the present study we aimed to clarify the endoscopic and molecular signatures of SSA/Ps, with and without CD. METHODS: A series of 208 serrated lesions, including 41 hyperplastic polyps, 90 SSA/Ps, 33 SSA/Ps with CD, and 44 traditional serrated adenomas, were observed and resected using magnifying endoscopy. BRAF and KRAS mutations and methylation of CIMP markers (MINT1, MINT2, MINT12, MINT31, and p16) were analyzed through pyrosequencing. Molecular alterations were then compared with endoscopic and pathologic characteristics. RESULTS: Among SSA/Ps without CD, the Type II-Open pit pattern (Type II-O), BRAF mutation, and CIMP were tightly associated with a proximal colon location. SSA/Ps in the distal colon infrequently exhibited Type II-O and CIMP. By contrast, most SSA/Ps with CD showed Type II-O plus adenomatous pit patterns (Type III or IV), BRAF mutation, and CIMP, irrespective of their locations. CONCLUSIONS: Our results suggest that the Type II-O plus III/IV pit pattern is a common feature of SSA/Ps with CD in both the proximal and distal colon and that this pit pattern is a hallmark of serrated lesions at high risk of developing into CRCs.

A strenuous experimental journey searching for spectroscopic evidence of a bridging nickel-iron-hydride in [NiFe] hydrogenase.

Direct spectroscopic evidence for a hydride bridge in the Ni-R form of [NiFe] hydrogenase has been obtained using iron-specific nuclear resonance vibrational spectroscopy (NRVS). The Ni-H-Fe wag mode at 675 cm(-1) is the first spectroscopic evidence for a bridging hydride in Ni-R as well as the first iron-hydride-related NRVS feature observed for a biological system. Although density function theory (DFT) calculation assisted the determination of the Ni-R structure, it did not predict the Ni-H-Fe wag mode at ∼ 675 cm(-1) before NRVS. Instead, the observed Ni-H-Fe mode provided a critical reference for the DFT calculations. While the overall science about Ni-R is presented and discussed elsewhere, this article focuses on the long and strenuous experimental journey to search for and experimentally identify the Ni-H-Fe wag mode in a Ni-R sample. As a methodology, the results presented here will go beyond Ni-R and hydrogenase research and will also be of interest to other scientists who use synchrotron radiation for measuring dilute samples or weak spectroscopic features.

Time-resolved coherent diffraction of ultrafast structural dynamics in a single nanowire.

The continuing effort to utilize the unique properties present in a number of strongly correlated transition metal oxides for novel device applications has led to intense study of their transitional phase state behavior. Here we report on time-resolved coherent X-ray diffraction measurements on a single vanadium dioxide nanocrystal undergoing a solid-solid phase transition, using the SACLA X-ray Free Electron Laser (XFEL) facility. We observe an ultrafast transition from monoclinic to tetragonal crystal structure in a single vanadium dioxide nanocrystal. Our findings demonstrate that the structural change occurs in a number of distinct stages attributed to differing expansion modes of vanadium atom pairs.

Structural characterization of CO-inhibited Mo-nitrogenase by combined application of nuclear resonance vibrational spectroscopy, extended X-ray absorption fine structure, and density functional theory: new insights into the effects of CO binding and the role of the interstitial atom.

The properties of CO-inhibited Azotobacter vinelandii (Av) Mo-nitrogenase (N2ase) have been examined by the combined application of nuclear resonance vibrational spectroscopy (NRVS), extended X-ray absorption fine structure (EXAFS), and density functional theory (DFT). Dramatic changes in the NRVS are seen under high-CO conditions, especially in a 188 cm(-1) mode associated with symmetric breathing of the central cage of the FeMo-cofactor. Similar changes are reproduced with the α-H195Q N2ase variant. In the frequency region above 450 cm(-1), additional features are seen that are assigned to Fe-CO bending and stretching modes (confirmed by (13)CO isotope shifts). The EXAFS for wild-type N2ase shows evidence for a significant cluster distortion under high-CO conditions, most dramatically in the splitting of the interaction between Mo and the shell of Fe atoms originally at 5.08 Å in the resting enzyme. A DFT model with both a terminal -CO and a partially reduced -CHO ligand bound to adjacent Fe sites is consistent with both earlier FT-IR experiments, and the present EXAFS and NRVS observations for the wild-type enzyme. Another DFT model with two terminal CO ligands on the adjacent Fe atoms yields Fe-CO bands consistent with the α-H195Q variant NRVS. The calculations also shed light on the vibrational "shake" modes of the interstitial atom inside the central cage, and their interaction with the Fe-CO modes. Implications for the CO and N2 reactivity of N2ase are discussed.