Timing of paediatric orchidopexy in universal healthcare systems: international administrative data cohort study.

BACKGROUND: International guidelines in 2008 recommended orchidopexy for undescended testis at 6-12 months of age to reduce the risk of testicular cancer and infertility. Using administrative data from England, Finland, Ontario (Canada), Scotland and Sweden (with data from Victoria (Australia) and Iceland in supplementary analyses), the aim of this study was to investigate compliance with these guidelines and identify potential socioeconomic inequities in the timing of surgery before 1 and 3 years. METHODS: All boys born in 2003-2011 with a diagnosis code of undescended testis and procedure codes indicating orchidopexy before their fifth birthday were identified from administrative health records. Trends in the proportion of orchidopexies performed before 1 and 3 years of age were investigated, as were socioeconomic inequities in adherence to the guidelines. RESULTS: Across all jurisdictions, the proportion of orchidopexies occurring before the first birthday increased over the study period. By 2011, from 7·6 per cent (Sweden) to 27·9 per cent (Scotland) of boys had undergone orchidopexy by their first birthday and 71·5 per cent (Sweden) to 90·4 per cent (Scotland) by 3 years of age. There was limited evidence of socioeconomic inequities for orchidopexy before the introduction of guidelines (2008). Across all jurisdictions for boys born after 2008, there was consistent evidence of inequities in orchidopexy by the first birthday, favouring higher socioeconomic position. Absolute differences in these proportions between the highest and lowest socioeconomic groups ranged from 2·5 to 5·9 per cent across jurisdictions. CONCLUSION: Consistent lack of adherence to the guidelines across jurisdictions questions whether the guidelines are appropriate.

ANTECEDENTES: En el 2008, las guías internacionales recomendaban efectuar una orquidopexia para los testículos no descendidos entre los seis y los 12 meses de edad para reducir los riesgos de cáncer testicular e infertilidad. Utilizando datos administrativos de Inglaterra, Finlandia, Ontario (Canadá), Escocia y Suecia (con datos de Victoria, Australia e Islandia para análisis complementarios), el objetivo de este estudio fue investigar el cumplimiento de estas guías y la identificación de posibles desigualdades socioeconómicas con relación al momento de la cirugía antes de 1 y 3 años de edad. MÉTODOS: A partir de los registros administrativos de salud, se identificaron todos los niños nacidos entre 2003 y 2011 con código diagnóstico de testículos no descendidos y con código de procedimiento correspondiente a orquidopexia antes de cumplir 5 años. Se investigaron las tendencias en la proporción de orquidopexias realizadas antes de 1 y 3 años de edad, respectivamente, al igual que las desigualdades socioeconómicas en el cumplimiento de las directrices de las guías. RESULTADOS: En todas las jurisdicciones, la proporción de orquidopexias realizadas antes del primer año de vida aumentó durante el periodo de estudio. En 2011, del 7,6% (Suecia) al 27,9% (Escocia) de los niños habían sido sometidos a orquidopexia en su primer año de vida y del 71,5% (Suecia) al 90,4% (Escocia) a los 3 años de edad. Hubo evidencia limitada de las inequidades socioeconómicas para la orquidopexia antes de la introducción de las guías (2008). En todas las jurisdicciones para los niños nacidos después de 2008, hubo evidencia consistente de inequidades para la práctica de una orquidopexia en el primer año de vida en favor de una posición socioeconómica más alta (socioeconomic position, SEP). Las diferencias absolutas en estas proporciones entre los grupos SEP más altos y más bajos oscilaron entre el 2,5% y el 5,9% en todas las jurisdicciones. CONCLUSIÓN: La falta de adherencia a las guías observada consistentemente en todas las jurisdicciones cuestiona si las guías son apropiadas.

The development and validation of a meta-tool for quality appraisal of public health evidence: Meta Quality Appraisal Tool (MetaQAT).

OBJECTIVES: Most quality appraisal tools were developed for clinical medicine and tend to be study-specific with a strong emphasis on risk of bias. In order to be more relevant to public health, an appropriate quality appraisal tool needs to be less reliant on the evidence hierarchy and consider practice applicability. Given the broad range of study designs used in public health, the objective of this study was to develop and validate a meta-tool that combines public health-focused principles of appraisal coupled with a set of design-specific companion tools. STUDY DESIGN: Several design methods were used to develop and validate the tool including literature review, synthesis, and validation with a reference standard. METHODS: A search of critical appraisal tools relevant to public health was conducted; core concepts were collated. The resulting framework was piloted during three feedback sessions with public health practitioners. Following subsequent revisions, the final meta-tool, the Meta Quality Appraisal Tool (MetaQAT), was then validated through a content analysis of appraisals conducted by two groups of experienced public health researchers (MetaQAT vs generic appraisal form). RESULTS: The MetaQAT framework consists of four domains: relevancy, reliability, validity, and applicability. In addition, a companion tool was assembled from existing critical appraisal tools to provide study design-specific guidance on validity appraisal. Content analysis showed similar methodological and generalizability concerns were raised by both groups; however, the MetaQAT appraisers commented more extensively on applicability to public health practice. CONCLUSIONS: Critical appraisal tools designed for clinical medicine have limitations for use in the context of public health. The meta-tool structure of the MetaQAT allows for rigorous appraisal, while allowing users to simultaneously appraise the multitude of study designs relevant to public health research and assess non-standard domains, such as applicability.

Impact of diabetes on healthcare costs in a population-based cohort: a cost analysis.

AIMS: To estimate the healthcare costs attributable to diabetes in Ontario, Canada using a propensity-matched control design and health administrative data from the perspective of a single-payer healthcare system. METHODS: Incident diabetes cases among adults in Ontario were identified from the Ontario Diabetes Database between 2004 and 2012 and matched 1:3 to control subjects without diabetes identified in health administrative databases on the basis of sociodemographics and propensity score. Using a comprehensive source of administrative databases, direct per-person costs (Canadian dollars 2012) were calculated. A cost analysis was performed to calculate the attributable costs of diabetes; i.e. the difference of costs between patients with diabetes and control subjects without diabetes. RESULTS: The study sample included 699 042 incident diabetes cases. The costs attributable to diabetes were greatest in the year after diagnosis [C$3,785 (95% CI 3708, 3862) per person for women and C$3,826 (95% CI 3751, 3901) for men], increasing substantially for older age groups and patients who died during follow-up. After accounting for baseline comorbidities, attributable costs were primarily incurred through inpatient acute hospitalizations, physician visits and prescription medications and assistive devices. CONCLUSIONS: The excess healthcare costs attributable to diabetes are substantial and pose a significant clinical and public health challenge. This burden is an important consideration for decision-makers, particularly given increasing concern over the sustainability of the healthcare system, aging population structure and increasing prevalence of diabetic risk factors, such as obesity.

Measurement of muon antineutrino quasielastic scattering on a hydrocarbon target at Eν ~ 3.5 GeV.

We have isolated ν(µ) charged-current quasielastic (QE) interactions occurring in the segmented scintillator tracking region of the MINERvA detector running in the NuMI neutrino beam at Fermilab. We measure the flux-averaged differential cross section, dσ/dQ², and compare to several theoretical models of QE scattering. Good agreement is obtained with a model where the nucleon axial mass, M(A), is set to 0.99 GeV/c² but the nucleon vector form factors are modified to account for the observed enhancement, relative to the free nucleon case, of the cross section for the exchange of transversely polarized photons in electron-nucleus scattering. Our data at higher Q² favor this interpretation over an alternative in which the axial mass is increased.

Measurement of muon neutrino quasielastic scattering on a hydrocarbon target at Eν ~ 3.5 GeV.

We report a study of ν(µ) charged-current quasielastic events in the segmented scintillator inner tracker of the MINERvA experiment running in the NuMI neutrino beam at Fermilab. The events were selected by requiring a µ- and low calorimetric recoil energy separated from the interaction vertex. We measure the flux-averaged differential cross section, dσ/dQ², and study the low energy particle content of the final state. Deviations are found between the measured dσ/dQ² and the expectations of a model of independent nucleons in a relativistic Fermi gas. We also observe an excess of energy near the vertex consistent with multiple protons in the final state.

Functional imaging of cognitive impairment in Parkinson's disease.

Parkinson's disease (PD) is known by most persons to be a neurodegenerative disorder that affects one's motor skills. However, the disease is also characterized by the less recognized cognitive symptoms, including deficits in executive functioning, as well as mood and behavioral problems, which are just as disabling and distressing as the motor symptoms. Imaging methods such as positron emission tomography (PET) have recently enhanced our understanding of cognitive disturbances in PD, and are reviewed in the current article. Furthermore, insights gained from the use of specific radiotracers in the dopaminergic and cholinergic neurotransmitter systems are discussed, as well as findings from in vivo detection of amyloid-beta. We will also discuss the potential use of a metabolic covariance network as a biomarker in clinical trials for the objective assessment of cognitive dysfunction in PD.

Structure and function of the perinucleolar compartment in cancer cells.

The perinucleolar compartment (PNC) is a subnuclear body that forms in cancer cells. In vivo analyses using human tumor tissues demonstrate a close correlation between PNC prevalence and disease progress in colorectal carcinoma, and a high PNC prevalence is associated with poor patient outcome. These findings are consistent with previous observations in breast cancer and cancer cell lines in vitro. The PNC is composed of thick strands that form a filamental meshwork often extending into the nucleolus. Although it appears to be electron dense as observed by transmission electron microscopy (TEM), the actual density of the structure imaged by electron spectroscopy is much lower, similar to that of the interchromatin space, and is lined with ribonucleoproteins (RNPs). In situ detections show that the PNC is highly enriched with a subset of small RNAs of polymerase III (Pol III) origins and RNA-binding proteins primarily implicated in pre-mRNA processing. A novel gel-shifting approach demonstrates that the addition of PNC-associated RNAs into HeLa cell lysates increases the mobility of polypyrimidine tract-binding (PTB) protein in a native gel electrophoresis, suggesting an interaction between these RNAs and PTB proteins. On the basis of these and other findings, we propose a working model in which novel RNPs have a key role in regulating gene expression at the PNC in cancer cells.

Effect of hypoxia on cellular adhesion to vitronectin and fibronectin.

Cellular invasion of extracellular matrix (ECM) occurs during normal and pathological settings. For cells to invade, they must adhere to the underlying substratum, break down barrier molecules, and detach from the substratum prior to migrating through the ECM. We previously demonstrated that incubation under reduced oxygen levels increases the in vitro invasiveness of trophoblast and breast carcinoma cells, an effect linked to elevated expression of the cell surface receptor for urokinase-type plasminogen activator (uPAR). This study examined the role of oxygen, integrins and the urokinase-type plasminogen activator (uPA) system on the adhesion of trophoblast and breast carcinoma cells to the ECM molecules vitronectin and fibronectin. Compared to exposure to 20 and 5% oxygen, exposure to 1% oxygen decreased adhesion of these cells to vitronectin and fibronectin, an effect that was reversible by re-exposure to 20% oxygen. Incubation in 1% oxygen also resulted in reduced expression of surface alpha(5) integrin. Furthermore, adhesion to vitronectin and fibronectin was reduced by compounds that interfere with integrin function, such as EDTA, anti-integrin antibodies, or by antibodies that interfere with the binding of pro-uPA to uPAR, soluble uPAR, soluble vitronectin, phosphatidylinositol-specific phospholipase C, as well as plasminogen activator inhibitor-1. These findings suggest an important role for oxygen in the regulation of cellular invasion, possibly in part through its effects on integrin and uPAR-mediated mechanisms of adhesion.

Structure and characterization of the glycan moiety of L-amino-acid oxidase from the Malayan pit viper Calloselasma rhodostoma.

Ophidian L-amino-acid oxidase (L-amino-acid oxygen:oxidoreductase, deaminating, EC 1.4.3.2) is found in the venom of many poisonous snakes (crotalids, elapids and viperids). This FAD-dependent glycoprotein has been studied from several snake species (e.g. Crotalus adamanteus, Crotalus atrox and Calloselasma rhodostoma) in detail with regard to the biochemical and enzymatic properties. The nature of glycosylation, however, as well as the chemical structure(s) of the attached oligosaccharide(s) are unknown. In view of the putative involvement of the glycan moiety in the biological effects of ophidian L-amino-acid oxidase, notably the apoptotic activity of the enzyme, structural knowledge is needed to evaluate its exact function. In this study we report on the glycosylation of L-amino-acid oxidase from the venom of the Malayan pit viper (Calloselasma rhodostoma). Its glycosylation is remarkably homogeneous with the major oligosaccharide accounting for approximately 90% of the total sugar content. Based on detailed analysis of the isolated oligosaccharide by 2D NMR spectroscopies and MALDI-TOF mass spectrometry the glycan is identified as a bis-sialylated, biantennary, core-fucosylated dodecasaccharide. The biological significance of this finding is discussed in light of the biological activities of the enzyme.

Subcellular localization and characterization of chorismate synthase in the apicomplexan Plasmodium falciparum.

The resurgence of drug-resistant apicomplexa, in particular Plasmodium falciparum, the most fatal human malarial parasite, has focused attention on the recent discovery of the shikimate pathway in these organisms, as it may provide the urgently required, novel drug targets resulting from the absence of this pathway in mammals. The direction of a parasiticidal drug design programme obviously requires knowledge of the subcellular localization and indeed full characterization of the possible enzyme targets. Here, we report the cloning and characterization of chorismate synthase from P. falciparum and present the first biochemical and immunological studies of an enzyme of the shikimate pathway from an apicomplexan parasite. We show that this chorismate synthase does not possess an intrinsic flavin reductase activity and is therefore monofunctional like the plant and bacterial chorismate synthases. Highest immunological cross-reactivity was found with a plant chorismate synthase. However, in contrast to the plant enzyme, which is located to the plastid, P. falciparum chorismate synthase is found in the parasite cytosol, akin to the fungal enzymes that possess an intrinsic flavin reductase activity (i.e. are bifunctional). Thus, P. falciparum chorismate synthase has a combination of properties that distinguishes it from other described chorismate synthases.

Chorismate synthase from the hyperthermophile Thermotoga maritima combines thermostability and increased rigidity with catalytic and spectral properties similar to mesophilic counterparts.

Chorismate synthase, the last enzyme in the shikimate pathway, catalyzes the transformation of 5-enolpyruvylshikimate 3-phosphate to chorismate, a biochemically unique reaction in that it requires reduced FMN as a cofactor. Here we report on the cloning, expression, and characterization of the protein for the first time from an extremophilic organism Thermotoga maritima which is also one of the oldest and most slowly evolving eubacteria. The protein is monofunctional in that it does not have an intrinsic ability to reduce the FMN cofactor and thereby reflecting the nature of the ancestral enzyme. Circular dichroism studies indicate that the melting temperature of the T. maritima protein is above 92 degrees C compared with 54 degrees C for the homologous Escherichia coli protein while analytical ultracentrifugation showed that both proteins have the same quaternary structure. Interestingly, UV-visible spectral studies revealed that the dissociation constants for both oxidized FMN and 5-enolpyruvylshikimate 3-phosphate decrease 46- and 10-fold, respectively, upon heat treatment of the T. maritima protein. The heat treatment also results in the trapping of the flavin cofactor in an apolar environment, a feature which is enhanced by the presence of the substrate 5-enolpyruvylshikimate 3-phosphate. Nevertheless, stopped-flow spectrophotometric evidence suggests that the mechanism of the T. maritima protein is similar to that of the E. coli protein. In essence, the study shows that T. maritima chorismate synthase exhibits considerably higher rigidity and thermostability while it has conserved features relevant to its catalytic function.

Multidisciplinary airway stent team: a comprehensive approach and protocol for tracheobronchial stent treatment.

Tracheobronchial stents are being used with increasing frequency to treat major airway obstruction from both malignant and benign processes. Traditionally, stents have been placed via rigid bronchoscopy, flexible bronchoscopy, or fluoroscopy by members of various individual disciplines. We describe a novel multidisciplinary airway stent team (MAST) protocol for tracheobronchial stent placement and endoscopic management of major airway obstruction. A patient with symptoms of airway obstruction is generally first evaluated with a computed tomography scan and a videotaped flexible bronchoscopy. These studies are reviewed by the team otolaryngologist, pulmonologist, and interventional radiologist. A treatment plan, including the type and location of stents and the need for adjuvant therapies, is formulated. Stent placement is performed in the operating room under general anesthesia. Rigid bronchoscopy, with flexible bronchoscopy and fluoroscopy as needed, allows precise stent placement and the best use of various therapeutic methods. The MAST protocol combines the skills, knowledge, and unique therapeutic options of specialists from otolaryngology, pulmonology, and interventional radiology. This approach allows optimal stent placement and the use of other endobronchial therapies, including laser ablation, balloon dilation, photodynamic therapy, cryotherapy, and brachytherapy. A protocol with representative case reports is presented, along with a review and comparison of several of our most commonly used stents. Otolaryngologists who practice bronchoesophagoscopy, by virtue of their operative skill and knowledge of airway management, are well equipped to become leaders of MASTs and are encouraged to initiate MASTs at their institutions.

Project back-on-track at 1 year: a delinquency treatment program for early-career juvenile offenders.

OBJECTIVE: This study assessed the effectiveness of Project Back-on-Track, an after-school diversion program that uses a multimodal approach for the treatment of early-career juvenile offenders. METHOD: Project Back-on-Track completers (30 of 41 enrollees; 73%), aged 9 to 17 years, 63% female, participated in a 4-week cycle of treatment consisting of group and family therapies, parent groups, educational sessions, community service projects, and empathy-building exercises. These youths attended the program 2 hours per day, 4 days a week, allowing for 32 hours of contact with the program per cycle; parents attended the program for 15 hours per cycle. Most youths were referred for violent offenses and met criteria for conduct disorder. RESULTS: Project Back-on-Track completers were significantly less likely than matched controls to have committed subsequent criminal offenses at 12 months. In addition, they had significantly fewer subsequent criminal charges at 9- and 12-month follow-up intervals than the control group. By decreasing the frequency of criminal recidivism, it is estimated that Project Back-on-Track resulted in savings to society of approximately $1,800 per youth enrolled after 1 year. CONCLUSION: At 1-year follow-up, findings suggest that treatment through Project Back-on-Track was effective in reducing criminal recidivism and costs in a population of early-career juvenile offenders.

Adriana and Luisa Castellucci award lecture 1999: role of oxygen in the regulation of trophoblast gene expression and invasion.

Changes in oxygen levels characterize normal and pathological human placentation. For example, relatively low Po(2)values are present around the blastocyst during implantation and in the placenta of the first trimester of pregnancy, a time of maximal trophoblast invasion. Our studies have revealed that low oxygen levels stimulate the in vitro invasiveness of cultured first trimester trophoblasts. This increased invasive ability is linked to elevated expression of some components of the plasminogen activator system and requires the participation of a putative haem protein. As gestation proceeds beyond the first trimester, and the extent of trophoblast invasion decreases, placental oxygen levels rise with a corresponding increase in blood flow. However, during certain pathological conditions, such as pre-eclampsia/intrauterine growth restriction, impaired remodelling of the uterine spiral arterioles leads to vessels with reduced diameters and localized regions of placental ischaemia/hypoxia. Placental hypoxia in the second half of gestation, as a consequence of reduced uteroplacental blood flow, may result in aberrant expression of genes that contribute to the pathophysiology of pre-eclampsia. Some of these genes encode certain cytokines and vasoactive molecules. We have also identified other genes whose expression is regulated by oxygen. Expression of one of them is induced in trophoblast and other cell types cultured under low oxygen levels and the product of the gene is a 43-kDa protein which we have termed PROXY-1. Compared to placental tissues and membranes isolated from uncomplicated pregnancies, PROXY-1 expression is elevated in tissues from pre-eclamptic pregnancies such as chorionic villi of peri-infarct regions, basal plate and membrane decidua, as well as chorion. Overall, these observations suggest that oxygen levels play an important role in placentation and in the pathophysiology of certain complications of pregnancy.

Upper airway complications of smoking.

Tobacco smoke has a myriad of acute and chronic effects on the upper airway. These problems can range from aggravating inflammatory reactions to life threatening malignancies. Cessation of smoking is the key to successful resolution of many upper airway complaints. An increased awareness of these disease processes can improve early diagnosis and appropriate treatment. A better awareness of these processes may facilitate physicians in counseling patients about smoking.

Antiproliferative actions of inhalational anesthetics: comparisons to the valproate teratogen.

The antiproliferative potential of the volatile anesthetics isoflurane, enflurane and sevoflurane was determined and compared to the valproate teratogen. The in vitro system employed, a G1 phase proliferative arrest endpoint in C6 glioma, has served previously to discriminate agents with known teratogenic potential in vivo. Based on estimated IC(50) values that were within twice the estimated minimum aveolar concentration value, the rank antiproliferative potency of the inhalational anesthetics employed was isoflurane=enflurane>>sevoflurane. Flow cytometric analysis of growth-arrested cell populations failed to reveal specific accumulation in any cell cycle phase and the lack of a G1 phase-specific effect was confirmed by the absence of a transient, time-dependent sialylation event in synchronized cells. The antiproliferative mechanism of volatile anesthetics, and valproate, was mediated at hydrophobic binding sites, as increasing the hydration sphere of the drug-micelle complex, using the hygroscopic qualities of the dimethylsulfoxide vehicle, completely reversed this effect. Our findings suggest inhalational anesthetics lack the specific in vitro characteristics of the valproate teratogen.

Employment and health among older bereaved men in the normative aging study: one year and three years following a bereavement event.

Research has indicated that the negative effects of bereavement on health among elderly men occur within the first six to twelve months following a bereavement event while other studies indicate that the death of a loved one can have long-term effects on social functioning and mental health (Arbuckle & DeVries, 1995; Vinick, 1983a). However, employment has been found to buffer the strain produced by stressful life events. The purpose of this study was to examine the differential effects of employment on physical and mental health between elderly men bereaved for one year and elderly men bereaved for two to three years. We selected two groups of men from the Normative Aging Study: those bereaved within the past year (N = 248) and those bereaved from two to three years (N = 262). Ordinary least squares multiple regression analyses examined the direct effect of employment, controlling for age, education, income, marital status, and stress, on physical and mental health among the two groups of men. Although there were no significant differences between the two groups of men, the results from the separate analyses indicated that employment had a direct positive effect on physical health among those bereaved for one year and those bereaved from two to three years, but no significant effects were observed on mental health. The results suggest that employment can benefit men soon after a bereavement event and also over a longer period of time, especially on physical health. Implications for clinical practice and future research are discussed.

Mechanical ventilation in hematopoietic stem cell transplantation: can We effectively predict outcomes?

BACKGROUND: Survival rates from mechanical ventilation (MV) in allogeneic bone marrow transplantation are poor, but little is known about the need for and outcomes from MV in patients who undergo autologous hematopoietic stem cell transplantation (AHSCT). STUDY OBJECTIVE: To determine the frequency of and risk factors for the use of MV in recipients of AHSCT and to identify predictors of survival in mechanically ventilated AHSCT patients. DESIGN: Retrospective, cohort analysis SETTING: Tertiary-care, university-affiliated medical center. PATIENTS: One hundred fifty-nine consecutive patients who underwent AHSCT. INTERVENTIONS: Patient surveillance and data collection. MEASUREMENTS AND RESULTS: The primary outcome measure was the need for MV, and the secondary end point was survival after MV. Of 159 patients, 17 required MV (10. 7%). Three variables were associated with the need for MV: increasing age, use of total body irradiation in the conditioning regimen, and treatment with amphotericin B. As a screening test to predict the need for MV, no risk factor had a sensitivity or specificity > 82%. Three of the 17 mechanically ventilated patients (17.6%) survived to discharge. Only the mean APACHE (acute physiology and chronic health evaluation) II score separated survivors from nonsurvivors (21.7 vs 31.4; p = 0.029). Both the duration of MV and the length of stay in the ICU were similar in survivors and nonsurvivors. CONCLUSIONS: We conclude that MV is infrequently needed following AHSCT. Although survival after MV in these patients is limited, clinical variables do not reliably allow clinicians to prospectively identify patients destined to die.

13C NMR study of how the oxyanion pKa values of subtilisin and chymotrypsin tetrahedral adducts are affected by different amino acid residues binding in enzyme subsites S1-S4.

A range of substrate-derived chloromethane inhibitors have been synthesized which have one to four amino acid residues. These have been used to inhibit both subtilisin and chymotrypsin. Using 13C NMR, we have shown that all except one of these inhibitors forms a tetrahedral adduct with chymotrypsin, subtilisin, and trypsin. From the pH-dependent changes in the chemical shift of the hemiketal carbon of the tetrahedral adduct, we are able to determine the oxyanion pKa in the different inhibitor derivatives. Our results suggest that in both the subtilisin and chymotrypsin chloromethane derivatives the oxyanion pKa is largely determined by the type of amino acid residue occupying the S1, subsite while binding in the S2-S4 subsites only has minor effects on oxyanion pKa values. Using free energy relationships, we determine that the different R groups of the amino acid residues binding in the S1 subsite only have minor effects on the oxyanion pKa values. We propose that the lower polarity of the chymotrypsin active site relative to that of the subtilisin active site explains why the oxyanion pKa is higher and more sensitive to the type of chloromethane inhibitor used in the chymotrypsin derivatives than in the subtilisin derivatives.