Pain Intensity, coping and maternal satisfaction in Low-Risk labouring Women: A prospective descriptive correlational study.

OBJECTIVES: The primary aim of the study was to explore pain intensity (PI) and pain coping (PC) scores and the relationship between them. The secondary aim was to explore the correlation between PI and PC scores with labour progress, parity, labour acceleration, labour augmentation and maternal satisfaction. METHODS: A prospective descriptive correlational study was conducted in a maternity hospital in Northern Italy. The sample included 54 low-risk women in active labour at term of pregnancy. A data record sheet was used to collect the relevant variables and the Italian Birth Satisfaction Scale Revised (I-BSS-R) was administered to participants at least 24 h after birth. RESULTS: In the first labour stage, the average PI score was 6.99 (SD = 1.95) and the average PC score was 6.5 (SD = 2.22). During the second labour stage, the average PI score was 7.75 (SD = 1.74) and the average PC score was 4.97 (SD = 2.76). The average PI score trend increased with labour progress. The average PC score improved between 4 and 7 cm of cervical dilatation. A significant positive correlation between PI scores and oxytocin augmentation (p < 0.001) and labour progression (p < 0.001) was noted. A significant positive correlation between PC scores and oxytocin augmentation (p = 0.02) was also observed. No significant differences were found for maternal satisfaction in regard to PI and PC scores. CONCLUSION: coping in labour do not solely depend on PI but also on labour progress and oxytocin augmentation. Additional support to empower women to cope with pain may be required in case of labour augmentation.

Genetic Drift Versus Climate Region Spreading Dynamics of COVID-19.

Background: The current propagation models of COVID-19 are poorly consistent with existing epidemiological data and with evidence that the SARS-CoV-2 genome is mutating, for potential aggressive evolution of the disease. Objectives: We looked for fundamental variables that were missing from current analyses. Among them were regional climate heterogeneity, viral evolution processes versus founder effects, and large-scale virus containment measures. Methods: We challenged regional versus genetic evolution models of COVID-19 at a whole-population level, over 168,089 laboratory-confirmed SARS-CoV-2 infection cases in Italy, Spain, and Scandinavia at early time-points of the pandemic. Diffusion data in Germany, France, and the United Kingdom provided a validation dataset of 210,239 additional cases. Results: Mean doubling time of COVID-19 cases was 6.63 days in Northern versus 5.38 days in Southern Italy. Spain extended this trend of faster diffusion in Southern Europe, with a doubling time of 4.2 days. Slower doubling times were observed in Sweden (9.4 days), Finland (10.8 days), and Norway (12.95 days). COVID-19 doubling time in Germany (7.0 days), France (7.5 days), and the United Kingdom (7.2 days) supported the North/South gradient model. Clusters of SARS-CoV-2 mutations upon sequential diffusion were not found to clearly correlate with regional distribution dynamics. Conclusion: Acquisition of mutations upon SARS-CoV-2 spreading failed to explain regional diffusion heterogeneity at early pandemic times. Our findings indicate that COVID-19 transmission rates are rather associated with a sharp North/South climate gradient, with faster spreading in Southern regions. Thus, warmer climate conditions may not limit SARS-CoV-2 infectivity. Very cold regions may be better spared by recurrent courses of SARS-CoV-2 infection.

The Prevalence of patients with panic attacks (PAs) and panic disorder (PD) visiting Emergency Departments of the Verona Hospital.

BACKGROUND: Panic Attacks (PAs) and Panic Disorder (PD) represent a heavy burden not only because of the difficulty in distinguishing them from other pathologies and in treating them appropriately but also because of their impact on public health worldwide. In Europe, PD constitutes one of the five most common mental disorders adversely affecting quality of life. STUDY DESIGN: The aim of this study is to evaluate the period prevalence of visits to the Emergency Departments of the University Hospital of Verona (North East of Italy) over the period between 2012-2016 because of symptoms of PAs or PD in order to quantify the burden of the disorder. METHODS: This study was carried out by retrospectively collecting data from the medical records of all the patients assessed at the Emergency Departments (EDs) of the Verona Hospital because of symptoms of PAs or PD over a 5-year period (1 January 2012 - 31 December 2016). The search words used in reviewing the medical records registered in the hospital discharge reports from the Gynecological, Pediatric and General Medicine Emergency Departments were: "Anxiety" and/or "Panic". A multiple logistic regression model was also created to evaluate the predictors of ED visits for PAs or PD over the period that was investigated. RESULTS: The study identified 3,771 cases of PAs or PD; 62.3% were females and 37.7% were males. The female-to-male ratio was 1.7:1. The mean age was 44 years (46 for the females and 41 for the males). The majority of the patients fell into two age categories: 30 to 39 (20.6%) and 40 to 49 (23.8%). The proportion of visits to the EDs for PAs or PD was approximately 20% per year, with an average of approximately 754 patients visiting the EDs every year. The period prevalence of accesses for PAs or PD over the five year period studied in the mean resident population (1.4%) and the mean visits to the EDs (2.5%) were calculated. Study results showed that the majority of the patients (80.9%) were referred to their general practitioner (GP) at the end of the assessment protocol at the EDs. According to the regression logistic model, the following variables were significant (p<0.05) risk factors for PAs or PD: being female vs. male (OR 1.899; 95% CI 1.785-2.020), being Italian vs. Foreigner (OR 1.292; 95% CI 1.174-1.421), having a white or green priority code at arrival (low urgency) vs. the other ones (OR 1.195; 95% CI 1.100-1.297), and being aged ≤42 years old (OR 1.091; 95% CI 1.024-1.161). CONCLUSION: The role of the GP is crucial in the management of PD and PAs. Given the difficulty of implementing primary and secondary prevention programs for these conditions, public health officials should make every effort to promote tertiary prevention in order to reduce the burden of the ailment and societal cost.

Timing of hospital admission in labour: latent versus active phase, mode of birth and intrapartum interventions. A correlational study.

BACKGROUND: Hospitalization of women in latent labour often leads to a cascade of unnecessary intrapartum interventions, to avoid potential disadvantages the recommendation should be to stay at home to improve women's experience and perinatal outcomes. AIM: The primary aim of this study was to investigate the association between hospital admission diagnosis (latent vs active phase) and mode of birth. The secondary aim was to explore the relationship between hospital admission diagnosis, intrapartum intervention rates and maternal/neonatal outcomes. METHODS: A correlational study was conducted in a large Italian maternity hospital. Data from January 2013 to December 2014 were collected from the hospital electronic records. 1.446 records of low risk women were selected. These were dichotomized into two groups based on admission diagnosis: 'latent phase' or 'active phase' of labour. FINDINGS: 52.7% of women were admitted in active labour and 47.3% in the latent phase. Women in the latent phase group were more likely to experience a caesarean section or an instrumental birth, artificial rupture of membranes, oxytocin augmentation and epidural analgesia. Admission in the latent phase was associated with higher intrapartum interventions, which were statistically correlated to the mode of birth. CONCLUSIONS: Women admitted in the latent phase were more likely to experience intrapartum interventions, which increase the probability of caesarean section. Maternity services should be organized around women and families needs, providing early labour support, to enable women to feel reassured facilitating their admission in labour to avoid the cascade of intrapartum interventions which increases the risk of caesarean section.

Situación epidemiológica de las intoxicaciones en argentina en 2014 / Epidemiological situation of poisonings in Argentina in 2014

INTRODUCCIÓN El conocimiento del impacto de las exposiciones a agentes tóxicos es indispensable para guiar las intervenciones de salud pública en materia de prevención y control de estos riesgos. OBJETIVOS Describir las intoxicaciones en Argentina en 2014 y las floraciones algales de cianobacterias en Entre Ríos, y definir estrategias de vigilancia. MÉTODOS Se realizó un estudio descriptivo con fuentes secundarias de datos de todo el país: registros de Centros de Información, Asesoramiento y Asistencia Toxicológica (CIAAT), notificaciones al Sistema Nacional de Vigilancia de la Salud (SNVS) y al Sistema de Vigilancia de Lesiones, siniestros laborales de la Superintendencia de Riesgos del Trabajo y defunciones registradas por la Dirección de Estadísticas e Información en Salud. En los CIAAT con mayor volumen de consultas se realizó un muestreo en dos etapas por conglomerados. Las floraciones algales se describieron con datos de la Comisión Administradora del Río Uruguay. RESULTADOS La mayor cantidad de consultas registradas por CIAAT correspondió a intoxicaciones medicamentosas (39,5%) en el rango de 0-4 años (45,7%), mientras que a través del SNVS fue mayoritaria la categoría "intoxicación por otros tóxicos" (31,92%), y en los siniestros laborales prevaleció "quemaduras y corrosiones en múltiples regiones del cuerpo". En cuanto a la mortalidad, la tasa fue de 1,16/100 mil habitantes, con un 44% de los casos por gases y vapores. Respecto a la carga de floraciones algales, se evidenció la zona del Embalse de Salto Grande de Federación a Concordia como la de mayor abundancia. DISCUSIÓN Existen distintas modalidades de registro de intoxicaciones. Incluso entre los CIAAT hay disparidad en las definiciones y criterios, lo que dificulta el análisis consolidado y la comparación. Se evidencia un importante subregistro. Los datos analizados muestran que el comportamiento de las intoxicaciones es similar al observado en otros países. Se recomienda un nuevo instrumento de recolección de datos para CIAAT y la implementación de Unidades Centinela.

Valoración de la exposición a plaguicidas en cultivos extensivos de la Argentina y su potencial impacto sobre la salud / Pesticides exposure assessment in extensive crops in Argentina and their potential impact on health

A nivel nacional no hay descripciones espaciales o analíticas para el diagnóstico deexposición a plaguicidas.ObjetivosDescribir la distribución espacial de la exposición a plaguicidas en Argentina y suasociación con indicadores de carga de cáncer. Construir índices incorporando prácticaslaborales y de vida, y validarlos con biomarcadores y salud de sujetos laboralmenteexpuestos y sus familias.MétodosPara describir la distribución espacial de la exposición y su asociación con indicadoresde carga de cáncer se construyeron dos índices globales: de exposición a plaguicidas(IEP) y de impacto ambiental total (IIAT). Se estudiaron sus distribuciones espaciales,y mediante un estudio ecológico nacional se analizó la asociación con las tasas demortalidad de cáncer total, mama y próstata. Otros dos índices de exposición construidoscon información individual de agroaplicadores de Córdoba fueron validados a partir deluso de resultados de biomarcadores (actividad de butirilcolinestrasa y genotoxicidad)y de salud de sujetos laboralmente expuestos; y se compararon con sus respectivoscontroles. Por último, se analizaron las condiciones de salud de niños de esas familias.ResultadosEl área pampeana agrupa IEP mayores al promedio nacional. Los mayores IIAT fueronpara 2,4-D y clorpirifos en igual zona. Los altos IIAT de cipermetrina y clorpirifos seasocian con más mortalidad de cáncer de mama; los de glifosato y clorimuron, conla de cáncer total en varones. Los síntomas generales, cardiorrespiratorios, dérmicosy daño genotóxico fueron mayores en aplicadores, pero no se asocian a niveles deexposición. Los niños presentan síntomas irritativos en un 30%; más de la mitad estánexpuestos a aplicaciones, vive a menos de 500 metros de depósitos y van a escuelas a500 metros de campos fumigados. Un 20% asiste en tareas de campo, sin elementosde protección personal ni cobertura de obra social

Double-blind evaluation and benchmarking of survival models in a multi-centre study.

Accurate modelling of time-to-event data is of particular importance for both exploratory and predictive analysis in cancer, and can have a direct impact on clinical care. This study presents a detailed double-blind evaluation of the accuracy in out-of-sample prediction of mortality from two generic non-linear models, using artificial neural networks benchmarked against a partial logistic spline, log-normal and COX regression models. A data set containing 2880 samples was shared over the Internet using a purpose-built secure environment called GEOCONDA (www.geoconda.com). The evaluation was carried out in three parts. The first was a comparison between the predicted survival estimates for each of the four survival groups defined by the TNM staging system, against the empirical estimates derived by the Kaplan-Meier method. The second approach focused on the accurate prediction of survival over time, quantified with the time dependent C index (C(td)). Finally, calibration plots were obtained over the range of follow-up and tested using a generalization of the Hosmer-Lemeshow test. All models showed satisfactory performance, with values of C(td) of about 0.7. None of the models showed a systematic tendency towards over/under estimation of the observed survival at tau=3 and 5 years. At tau=10 years, all models underestimated the observed survival, except for COX regression which returned an overestimate. The study presents a robust and unbiased benchmarking methodology using a bespoke web facility. It was concluded that powerful, recent flexible modelling algorithms show a comparative predictive performance to that of more established methods from the medical and biological literature, for the reference data set.

Characterization and pharmacological actions of tecostanine, an alkaloid of Tecoma stans.

Tecostanine (1) was isolated from Tecoma stans leaves. Its sterochemistry was elucidated as well as its antihyperglycemic activity and its affinity to opioid and nicotinic receptors. The oxalate salt of 1 did not significantly affect blood glucose levels in normoglycaemic and hyperglycaemic rats. It did not appear to interact with opioid receptors (mu type) and showed only moderate affinity to the nicotinic receptor.

Synthesis, absolute configuration and antimuscarinic activity of the enantiomers of [1-(2,2-diphenyl-[1,3]dioxolan-4-yl)-ethyl]-dimethyl-amine.

Methylation of the carbon atom C of compound 1, a potent and not selective muscarinic antagonist, was carried out. The resulting diastereomers were separated and the corresponding racemate further resolved to give four enantiomers, which were tested both as hydrogen oxalate and methiodide salts. The pharmacological results obtained at M1, M2 and M3 muscarinic receptor subtypes, show that methylation at C1, depending on the stereochemistry, increases antagonist potency, having thus the same effect of nitrogen quaternization. These results may well lead to the development of new potent antimuscarinic drugs lacking a cationic head.

Structural bases for the inhibition of aldose reductase by phenolic compounds.

Aldose reductase (ALR2) is an enzyme involved in the development of long-term diabetic complications. In the search for aldose reductase inhibitors less acidic than carboxylic acids, phenolic compounds related to benzopyran-4-one and chalcone are particularly interesting because they possess good inhibitory properties. In order to investigate the similarities between these two classes of compounds and to provide a structural basis for their inhibition of ALR2, the existing structure-activity relationships were reconsidered. To this end, the acidity constants of a set of chalcones were measured and compared with those of benzopyran-4-one derivatives. Then, having established the relevant protonation state of these phenolics at physiological pH, a conformational analysis was performed on the most active benzopyran-4-one and chalcone derivatives and the results were compared with the crystal structures of some analogues. Finally, molecular docking of the most active chalcone into the ALR2 binding site was performed, and the structure of the enzyme-inhibitor complex was compared with that of the complex formed between ALR2 and a previously-obtained benzopyran-4-one derivative.

1-Benzopyran-4-one antioxidants as aldose reductase inhibitors.

Starting from the inhibitory activity of the flavonoid Quercetin, a series of 4H-1-benzopyran-4-one derivatives was synthesized and tested for inhibition of aldose reductase, an enzyme involved in the appearance of diabetic complications. Some of the compounds obtained display inhibitory activity similar to that of Sorbinil but are more selective than Quercetin and Sorbinil with respect to the closely related enzyme, aldehyde reductase, and also possess antioxidant activity. Remarkably, these compounds possess higher pKa values than carboxylic acids, a characteristic which could make the pharmacokinetics of these compounds very interesting. Molecular modeling investigations on the structures of inhibitors bound at the active site of aldose reductase were performed in order to suggest how these new inhibitors might bind to the enzyme and also to interpret structure-activity relationships.

Synthesis and alpha-adrenoceptor blocking activity of the enantiomers of benzyl-(2-chloroethyl)-[2-(2-methoxyphenoxy)-1-methylethyl]amine hydrochloride.

The enantiomers of benzyl-(2-chloroethyl)-[2-(2-methoxyphenoxy) -1-methylethyl]amine hydrochloride (1, CM18) were synthesized and studied pharmacologically for their irreversible antagonism at rat vas deferens alpha-adrenoceptors. In addition, assignment of the absolute configuration of the two enantiomers of 1 was made by X-ray crystallographic analysis performed on the intermediate amine (+)-2 hydrochloride. The enantiomer (R)-(+)-1 [(R)-(+)-CM18] (a) had a 10-fold preferential blocking activity for alpha 1-versus alpha 2-adrenoceptors, (b) discriminated, like racemic 1, between two possible alpha 1-adrenoceptor subsites/subtypes, with a selectivity ratio of 6.5 and (c) was 10-23 times as potent as the (S)-(-)-enantiomer at alpha 2- and alpha 1-adrenoceptors. Thus, it may be a valuable tool for the characterization of rat vas deferens alpha 1-adrenoceptor subtypes.

Synthesis, antimicrobial and genotoxic properties of some benzoimidazole derivatives.

A number of 1H-benzoimidazol-2-ylamine and of 1-methyl-1H-benzoimidazol-2-ylamine derivatives were synthesized and the crystal and molecular structure of N-[4-(2-amino-benzoimidazole-1-sulfonyl)-phenyl] acetamide was determined by X-ray diffraction analysis. The compounds obtained were investigated for antimicrobial and genotoxic activities.

Polyhydroxyoligothiophenes. 2. Hydrogen-Bonding-Oriented Solid State Conformation of 3,3'-Bis(2-hydroxyethyl)-2,2'-bithiophene and Regioselective Synthesis of the Corresponding Head-to-Head/Tail-to-Tail Quater- and Sexithiophene.

This paper reports the X-ray structure of 3,3'-bis(2-hydroxyethyl)-2,2'-bithiophene (1), which is the building block for the synthesis of head-to-head/tail-to-tail 2-hydroxyethyl-substituted oligothiophenes. Contrary to all the bithiophenes reported so far, 1 exhibits a noncoplanar anti conformation and an inter-ring twist angle (67.5 degrees ) which is the largest ever measured for adjacent rings of alpha-conjugated oligothiophenes. This unusual conformation appears to be dictated by intermolecular hydrogen-bonding interactions involving the OH groups, which bind the molecule in close packed layers. The paper also describes the regioselective synthesis of the dimer and the trimer of 1, namely of 3,3',4",3"'-tetrakis(2-hydroxyethyl)-2,2':5',2":5",2"'-quaterthiophene (3c) and of 3,3',4",3"',4"",3""'-hexakis(2-hydroxyethyl)-2,2':5',2":5",2"':5"',2"":5"",2""'-sexithiophene (4b). 3c And 4b were obtained through palladium(0)-catalyzed coupling of the mono- and distannanes of the tetrahydropyranyl derivative of 1 with the appropriate monobromo compound (Stille's reaction). Finally, the paper reports force-field calculations which suggest that the low lambda(max) values measured for 1, 3c, and 4b are also the result of intramolecular hydrogen-bonding interactions which favor highly twisted conformations in solution.

Crystal structure solution and refinement of the semisynthetic cobalt-substituted bovine erythrocyte superoxide dismutase at 2.0 A resolution.

The semisynthetic Co-substituted bovine erythrocyte superoxide dismutase (SOD) has been crystallized in a new crystalline form and the structure determined at 2.0 A (1 A = 0.1 nm) resolution. The crystals belong to space group P2(1)2(1)2(1) with cell constants: a = 51.0, b = 147.6, c = 47.5 A, and contain one dimeric molecule of 32,000 M(r) per asymmetric unit. The structure has been solved by molecular replacement techniques using the Cu,Zn bovine enzyme as a search model, and refined by molecular dynamics with the crystallographic pseudo-energy term, followed by conventional crystallographic refinement. The R-factor for the 18,964 unique reflections in the resolution range from 10.0 to 2.0 A is 0.176 for a model comprising 2188 protein atoms and 200 solvent molecules; the root-mean-square deviation from the ideal bond lengths is 0.010 A, and the average atomic temperature factor is 26.5 A2. The dimeric molecule of the enzyme is composed of two identical subunits related by a non-crystallographic 2-fold axis. The subunit has as its structural scaffolding the conventional SOD-flattened antiparallel eight-stranded beta-barrel, with three external loops. The co-ordination geometry of the metal center in the active site is fairly well preserved when compared with the native Cu,Zn bovine enzyme. Co2+ is in tetrahedral co-ordination, while the Cu2+ ligands show an uneven distortion from the square planar geometry. The least-squares superposition of the metals ligands and the catalytically important Arg141 of the native and Co-substituted enzyme yields a root-mean-square value of 0.401 A, the largest deviation occurring at the Co2+ ligand Asp81. An additional copper ligand, compatible with a water molecule, is observed at 2.38 A from Cu2+ in the active-site channel, at the supposed binding site of the O2- anion substrate. Several ordered water molecules have been observed on the protein surface and in the active-site channel; their structural locations coincide remarkably with those of related water molecules found in the crystal structure of the phylogenetically distant superoxide dismutase from yeast.

Crystal structure of yeast Cu,Zn superoxide dismutase. Crystallographic refinement at 2.5 A resolution.

The structure of Cu,Zn yeast superoxide dismutase has been determined to 2.5 A resolution. The enzyme crystallizes in the P2(1)2(1)2 space group with two dimeric enzyme molecules per asymmetric unit. The structure has been solved by molecular replacement techniques using the dimer of the bovine enzyme as the search model, and refined by molecular dynamics with crystallographic pseudo-energy terms, followed by conventional crystallographic restrained refinement. The R-factor for 32,088 unique reflections in the 10.0 to 2.5 A resolution range (98.2% of all possible reflections) is 0.158 for a model comprising two protein dimers and 516 bound solvent molecules, with a root-mean-square deviation of 0.016 A from the ideal bond lengths, and an average B-factor value of 29.9 A2. A dimeric molecule of the enzyme is composed of two identical subunits related by a non-crystallographic 2-fold axis. Each subunit (153 amino acid residues) has as its structural scaffolding a flattened antiparallel eight-stranded beta-barrel, plus three external loops. The overall three-dimensional structure is quite similar to the phylogenetically distant bovine superoxide dismutase (55% amino acid homology), the largest deviations can be observed in the regions of amino acid insertions. The major insertion site hosting residues Ser25A and Gly25B, occurs in the 2,3 beta-turn between strands 2b and 3c, resulting in the structural perturbations of the two neighbouring strands. The second insertion site, at the end of the 3c beta-strand in the wide Greek-key loop, hosts the Asn35A residue, having an evident effect on the structure of the loop and possibly on the neighbouring 5,4 beta-turn. The salt bridge Arg77-Asp99 and the disulphide bridge Cys55-Cys144 stabilize the loop regions containing the metal ligands. The stereochemistry of the two metal centres is conserved, with respect to the bovine enzyme. The Cu2+ ligands show an uneven distortion from a square plane, while Zn2+ co-ordination geometry is distorted tetrahedral. The imidazole ring of the His61 residue forms a bridge between Cu and Zn ions. A solvent peak compatible with a fifth ligand is observed 2.0 A away from the copper in the active site channel, which is filled by ordered water molecules that possibly contribute to the stability and function of the enzyme. The charged residues responsible for the electrostatic guidance of the substrate to the active site (Glu130, Glu131, Lys134 and Arg141) are fairly conserved in their positions, some of them showing different interactions in the four chains due to the intermolecular contacts between the dimers.(ABSTRACT TRUNCATED AT 400 WORDS)

Structure solution and molecular dynamics refinement of the yeast Cu,Zn enzyme superoxide dismutase.

Cu,Zn yeast superoxide dismutase was crystallized from polyethylene glycol solutions. The crystals belong to the P2(1)2(1)2 space group, with cell dimensions a = 105.3, b = 143.0, c = 62.1 A; two dimers of Mr = 32,000 each are contained in the asymmetric unit. Diffraction data at 2.5 A resolution were collected with the image-plate system at the EMBL synchrotron radiation facility in Hamburg. The structure was determined by molecular replacement using as a search model the 'blue-green' dimer of the bovine Cu,Zn superoxide dismutase. The crystallographic refinement of the molecular replacement solution was performed by means of molecular dynamics techniques and resulted in an R factor of 0.268 for the data between 6.0 and 2.5 A. The model was subsequently subjected to conventional restrained crystallographic refinement of the coordinates and temperature factors. The current R value for the data between 6.0 and 2.5 A is 0.220. Owing to the large radius of convergence of the molecular dynamics-crystallographic refinement, the convergence of the refinement process was reached after 18.1 ps of simulation time. The geometry of the active site of the enzyme appears essentially preserved compared with the bovine superoxide dismutase. The beta-barrel structure in the yeast enzyme is closed at the upper part by an efficient hydrogen-bonding scheme.

X-ray crystal structure of the bovine alpha-chymotrypsin/eglin c complex at 2.6 A resolution.

The crystal structure of the molecular complex formed by bovine alpha-chymotrypsin and the recombinant serine proteinase inhibitor eglin c from Hirudo medicinalis has been solved using monoclinic crystals of the complex, reported previously. Four circle diffractometer data at 3.0 A resolution were employed to determine the structure by molecular replacement techniques. Bovine alpha-chymotrypsin alone was used as the search model; it allowed us to correctly orient and translate the enzyme in the unit cell and to obtain sufficient electron density for positioning the eglin c molecule. After independent rigid body refinement of the two complex components, the molecular model yielded a crystallographic R factor of 0.39. Five iterative cycles of restrained crystallographic refinement and model building were conducted, gradually increasing resolution. The current R factor at 2.6 A resolution (diffractometer data) is 0.18. The model includes 56 solvent molecules. Eglin c binds to bovine alpha-chymotrypsin in a manner consistent with other known serine proteinase/inhibitor complex structures. The reactive site loop shows the expected conformation for productive binding and is in tight contact with bovine alpha-chymotrypsin between subsites P3 and P'2; Leu 451 acts as the P1 residue, located in the primary specificity S1 site of the enzyme. Hydrogen bonds equivalent to those observed in complexes of trypsin(ogen) with the pancreatic basic- and secretory-inhibitors are found around the scissile peptide bond.