Intercalation of anticancer drug Palbociclib with calf-thymus DNA: new insights from molecular spectroscopic, molecular dynamic simulations and cleavage studies.

The interaction between the anti-cancer drug Palbociclib (PAL) and calf-thymus DNA (CT-DNA) was investigated using various biophysical techniques in a physiological buffer (pH 7.4). It was found that PAL intercalated into the base pairs of CT-DNA as evidenced from the results of UV-Vis, fluorescence, circular dichroism (CD), competitive binding assay with ethidium bromide (EB) and Hoechst 33258, KI quenching study, the effect of denaturing agent and viscosity measurements. The magnitude of binding constants (106 M-1) at different temperatures suggested strong binding between PAL and CT-DNA during complexation. The observed ΔHo > 0 and ΔSo > 0 indicated that the binding process is primarily driven by hydrophobic interactions. Molecular docking studies indicated partial intercalation of pyridopyrimidine ring between the base pairs of DNA. Free energy surface (FES) analysis derived from metadynamics simulation studies revealed the PAL-induced cleavage of DNA, which was confirmed by gel electrophoresis experiments.Communicated by Ramaswamy H. Sarma.

Reconnecting the Hand and Arm to the Brain: Efficacy of Neural Interfaces for Sensorimotor Restoration after Tetraplegia.

Background: Paralysis after spinal cord injury involves damage to pathways that connect neurons in the brain to peripheral nerves in the limbs. Re-establishing this communication using neural interfaces has the potential to bridge the gap and restore upper extremity function to people with high tetraplegia. Objective: We report a novel approach for restoring upper extremity function using selective peripheral nerve stimulation controlled by intracortical microelectrode recordings from sensorimotor networks, along with restoration of tactile sensation of the hand using intracortical microstimulation. Methods: A right-handed man with motor-complete C3-C4 tetraplegia was enrolled into the clinical trial. Six 64-channel intracortical microelectrode arrays were implanted into left hemisphere regions involved in upper extremity function, including primary motor and sensory cortices, inferior frontal gyrus, and anterior intraparietal area. Nine 16-channel extraneural peripheral nerve electrodes were implanted to allow targeted stimulation of right median, ulnar (2), radial, axillary, musculocutaneous, suprascapular, lateral pectoral, and long thoracic nerves, to produce selective muscle contractions on demand. Proof-of-concept studies were performed to demonstrate feasibility of a bidirectional brain-machine interface to restore function of the participant's own arm and hand. Results: Multi-unit neural activity that correlated with intended motor action was successfully recorded from intracortical arrays. Microstimulation of electrodes in somatosensory cortex produced repeatable sensory percepts of individual fingers for restoration of touch sensation. Selective electrical activation of peripheral nerves produced antigravity muscle contractions. The system was well tolerated with no operative complications. Conclusion: The combination of implanted cortical electrodes and nerve cuff electrodes has the potential to allow restoration of motor and sensory functions of the arm and hand after neurological injury.

Gait Training with Robotic Exoskeleton Assisted Rehabilitation System in Patients with Incomplete Traumatic and Non-Traumatic Spinal Cord Injury: A Pilot Study and Review of Literature.

Objective: This pilot study aimed to assess the safety and feasibility of robotic gait training and its' effects on gait parameters in individuals with incomplete motor spinal cord injury-SCI (AIS C and AIS D). Methods: The study was conducted in a tertiary research center with indigenously developed Robotic Exoskeleton Assisted Rehabilitation Systems (REARS). Primary outcome measures used were the ten-meter walk test (10MWT), two-minute walk test (2MWT), six-minute walk test (6MWT), the timed up and go test (TUG), the walking index for spinal cord injury II (WISCI II), and the spinal cord independence measure version III (SCIM III) at baseline, 12 sessions, and after 24 sessions (endpoint) of training. At baseline, individuals who could not perform 10MWT, TUG, and 6MWT were grouped in G1 for analysis. Participants in G2 were able to perform all the tests at baseline. Results: The median (interquartile range [IQR]) age and duration of illness was 41 (24) years and 167 (147) days, respectively. Five out of seven participants had non-traumatic etiology and five were males. After completing training, participants in G1 were able to complete the 10MWT, 6MWT, and TUG, and the mean (SD) scores were 0.2 m/s (0.2), 66.3 m (61.2) and 113.3 s (117.4), respectively. Participants in G2 could perform the TUG test 13.5 s faster at the end of the study (11.9 s vs 25.4 s). The minimum clinically important difference (MCID) for TUG was 10.8 s. In G2, the pre-post training change in mean score of 10MWT and 6MWT was 0.11 m/s and 42 m, respectively; these values approached the MCID for these measures. None of the participants had any injury during training. Conclusions: Robotic gait training with REARS is safe and feasible. Such training may lead to an improvement in balance and walking capacity.

Interobserver agreement between eight observers using IOTA simple rules and O-RADS lexicon descriptors for adnexal masses.

PURPOSE: To evaluate interobserver agreement in assigning imaging features and classifying adnexal masses using the IOTA simple rules versus O-RADS lexicon and identify causes of discrepancy. METHODS: Pelvic ultrasound (US) examinations in 114 women with 118 adnexal masses were evaluated by eight radiologists blinded to the final diagnosis (4 attendings and 4 fellows) using IOTA simple rules and O-RADS lexicon. Each feature category was analyzed for interobserver agreement using intraclass correlation coefficient (ICC) for ordinal variables and free marginal kappa for nominal variables. The two-tailed significance level (a) was set at 0.05. RESULTS: For IOTA simple rules, interobserver agreement was almost perfect for three malignant lesion categories (M2-4) and substantial for the remaining two (M1, M5) with k-values of 0.80-0.82 and 0.68-0.69, respectively. Interobserver agreement was almost perfect for two benign feature categories (B2, B3), substantial for two (B4, B5) and moderate for one (B1) with k-values of 0.81-0.90, 0.69-0.70 and 0.60, respectively. For O-RADS, interobserver agreement was almost perfect for two out of ten feature categories (ascites and peritoneal nodules) with k-values of 0.89 and 0.97. Interobserver agreement ranged from fair to substantial for the remaining eight feature categories with k-values of 0.39-0.61. Fellows and attendings had ICC values of 0.725 and 0.517, respectively. CONCLUSION: O-RADS had variable interobserver agreement with overall good agreement. IOTA simple rules had more uniform interobserver agreement with overall excellent agreement. Greater reader experience did not improve interobserver agreement with O-RADS.

Assessing donor-recipient size metrics for heart transplant outcomes: UNOS database analysis.

STUDY: There is no widely accepted donor to recipient size-match metric to predict outcomes in cardiac transplant. The predictive ability of size-match metrics has not been studied when recipients are stratified by heart failure etiology. We sought to assess the performance of commonly used size metrics to predict survival after heart transplant, accounting for restrictive versus non-restrictive pathology. METHODS: The UNOS registry was queried from 2000 to 2017 for all primary isolated heart transplants. Donor-recipient ratios were calculated for commonly used size metrics and their association with survival was assessed using continuous, nonlinear analysis. RESULTS: 29 817 patients were identified. Height (P < .001), predicted heart mass (PHM) (P = .003), ideal body weight (IBW) (P < .001) and body mass index (BMI) (P = .003) ratios were significantly associated with survival, while weight and body surface area (BSA) ratios were not. When stratified, only BMI ratio retained significance for both restrictive (P = .051) and non-restrictive (P = .003) subsets. Recipients with restrictive etiology had increased risk of mortality with both a lower and higher BMI ratio. CONCLUSIONS: While many metrics show association with survival in the non-restrictive subset, BMI is the only metric that retains significance in the restrictive subset. Recipients with restrictive and non-restrictive etiologies of heart failure tolerate size mismatch differently.

Continuous-flow LVAD exchange to a different pump model: Systematic review and meta-analysis of the outcomes.

Despite improved outcomes of modern continuous-flow left ventricular assist devices (CF-LVADs), device exchange is still needed for various indications. While the majority of CF-LVADs are exchanged to the same model, exchange to a different pump model is occasionally warranted. In this meta-analysis, we sought to consolidate the existing evidence to better elucidate the indications and outcomes in these cases. A comprehensive systematic search of adult patient cohorts who underwent CF-LVAD exchange to a different CF-LVAD model was performed. Study-level data from 10 studies comprising 98 patients were extracted and pooled for analysis. Mean patient age was 58 (95% CI: 48-65) and 81% were male. Indication for initial CF-LVAD was ischemic cardiomyopathy in 45% (34-57). Initial device was HeartMate II LVAD (HMII) in 93 (94.9%) and HeartWare HVAD (HW) in 5 (5.1%) patients. After mean CF-LVAD support time of 18.8 (15.2-22.4) months, exchange indications included thrombosis in 71% (43-89), infection in 21% (8-47) and device malfunction in 12% (7-21). HMII to HW exchange occurred in 53 (54.1%) patients, HMII to HeartMate III (HM3) in 32 (32.7%), and HM II to either HW or HM3 in 13 (13.2%) patients. Postoperatively, right ventricular assist device was required in 16% (8-32). Overall, 20% (8-40) of patients experienced a stroke, while HW patients had a significantly higher stroke incidence than HM3 patients (HW: 21% (8-47) vs. HM3: 5% (1-24), P < .01). Overall 30-day mortality was 10% (6-17), while HW had a significantly worse 30-day mortality than HM3 (HW: 13% (7-24) vs. HM3: 5% (1-24), P = .03). Following device exchange from a different CF-LVAD model, HM3 is associated with lower stroke and higher survival when compared to HW.

Effect of conductive hydro-drying on physiochemical and functional properties of two pulse protein extracts: Green gram (Vigna radiata) and black gram (Vigna mungo).

In this study, the effect of two drying methods (conductive hydro-drying - CHD and freeze-drying - FD) on the physical and functional properties of green gram (GG) and black gram (BG) protein powders was investigated. CHD dried protein powder showed excellent powder characteristics with moisture contents ranging from 3 to 6%, water activity of ~0.4 and Carr index ≤10. The CHD samples were dried in 210 min; with higher drying rates, CHD samples showed no significant changes in powder characteristics, color value, and water and oil absorption indices. The solubility of both proteins were found to be lower at pH 4 to 7 and higher at pH 1, 2, 8, 9 and 10; at certain pH, the solubility of CHD protein was higher than that of the FD counterparts. No significant differences were observed in the oil absorption capacity, surface hydrophobicity, protein gel formation, pasting and thermal properties. XRD and FTIR analyses were used to explain changes in protein structure and the presence of both α-helix and ß-sheet was observed, with higher ß-sheet levels in both pulses dried using CHD. Results confirmed that CHD, a variant of the refractance window drying (RWD) offered protein quality in par with FD.

Outcomes of Mechanical Circulatory Support for Giant Cell Myocarditis: A Systematic Review.

Treatment of giant cell myocarditis (GCM) can require bridging to orthotopic heart transplantation (OHT) or recovery with mechanical circulatory support (MCS). Since the roles of MCS and immunotherapy are not well-defined in GCM, we sought to analyze outcomes of patients with GCM who required MCS. A systematic search was performed in June 2019 to identify all studies of biopsy-proven GCM requiring MCS after 2009. We identified 27 studies with 43 patients. Patient-level data were extracted for analysis. Median patient age was 45 (interquartile range (IQR): 32-57) years. 42.1% (16/38) were female. 34.9% (15/43) presented in acute heart failure. 20.9% (9/43) presented in cardiogenic shock. Biventricular (BiVAD) MCS was required in 76.7% (33/43) of cases. Of the 62.8% (27/43) of patients who received immunotherapy, 81.5% (22/27) used steroids combined with at least one other immunosuppressant. Cyclosporine was the most common non-steroidal agent, used in 40.7% (11/27) of regimens. Immunosuppression was initiated before MCS in 59.3% (16/27) of cases, after MCS in 29.6% (8/27), and not specified in 11.1% (3/27). Immunosuppression started prior to MCS was associated with significantly better survival than MCS alone (p = 0.006); 60.5% (26/43) of patients received bridge-to-transplant MCS; 39.5% (17/43) received bridge-to-recovery MCS; 58.5% (24/41) underwent OHT a median of 104 (58-255) days from diagnosis. GCM recurrence after OHT was reported in 8.3% (2/24) of transplanted cases. BiVAD predominates in mechanically supported patients with GCM. Survival and bridge to recovery appear better in patients on immunosuppression, especially if initiated before MCS.

Utilization of gum polysaccharide of Araucaria heterophylla and Azadirachta indica for encapsulation of cyfluthrin loaded super paramagnetic iron oxide nanoparticles for mosquito larvicidal activity.

Surface engineering of super paramagnetic iron oxide nanoparticles (SPIONs) favor the tagging of any molecule or compound onto it, encapsulating them with a biopolymer make them biocompatible and favor slow release of loaded molecules. Recovery of SPIONs is easier as they obey to external magnetic field. In this study, SPIONS were used for mosquito larvicidal activity after surface engineered with oleic acid to favor the tagging of Cyfluthrin (mosquito larvicidal agent), it was then encapsulated with gum polysaccharide derived from Azadirachta indica and Araucaria heterophylla. Every stage of coreshell formation was microscopically and spectroscopically characterized. The coreshell SPIONs produced using Azadirachta indica and Araucaria heterophylla gum derived polysaccharide encapsulation were found to be the size around 80 nm. Thus, prepared coreshell SPIONs was subjected for mosquito larvicidal activity against Culex sp. The coreshell SPIONs was efficiently killing the mosquito larva and its impact was studied by percentage mortality studies.

A prospective observational study of the follow-up of medical management of early pregnancy failure.

BACKGROUND: Medical termination for missed miscarriage with the use of 800 µg of vaginal misoprostol as a single agent is recommended as a cheap option before 14 weeks of gestation in developing countries. A few studies have looked at its efficacy. METHODS: A prospective, observational study was done on women having medical termination with up to three doses of 800 µg vaginal misoprostol at 12 hourly intervals. The number of women who needed check curettage was collected. Ultrasound findings if done were collated. Follow-up was done telephonically at the end of first week, fourth week and sixth week. RESULTS: The cohort comprised 145 women. The primary outcome was the need for curettage after expulsion of products following medical management and this was 49/145 (37.8%) of women. The induction expulsion interval was 36 hours. The mean endometrial thickness of the 113/145 women who had an ultrasound was 11 mm. The mean endometrial thickness in women who had check curettage was 18 mm. Persistent spotting was the only significant symptom at follow-up. Resumption of cycle at the end of the sixth week was seen in 105/132 (80.15%) of women who were followed up. CONCLUSION: Findings of our study showed the check curettage rate of 37.8%. However, the regime which we used, that is, 800 µg vaginal misoprostol at 12 hourly intervals had a long induction to expulsion interval of 36 hours. In all, 80% of women resumed normal cycles at the end of the sixth week. No significant complications were noted on follow-up.

Purification, characterization and utilization of polysaccharide of Araucaria heterophylla gum for the synthesis of curcumin loaded nanocarrier.

In this study, gum of Araucaria heterophylla was collected. The collected gum was subjected for extraction of polysaccharide using solvent extraction system. Thus, extracted polysaccharide was further purified using solvent method and was characterized using UV-Vis spectroscopy, Phenol sulfuric acid assay, FTIR, TGA, TLC and GC-MS. The gum derived polysaccharide was found to have the following sugars Rhamnose, Allose, Glucosinolate, Threose, Idosan, Galactose and Arabinose. The extracted polysaccharide was tested for various in-vitro bioactive studies such as antibacterial activity, antioxidant activity and anticancer activity. The polysaccharide was found to have antioxidant and anticancer activity. Further, the polysaccharide was subjected for carboxymethylation to favor the nanocarrier synthesis, where it was chelated using Sodium Tri Meta Phosphate (STMP) to form nanocarriers. The nanocarriers so formed were loaded with curcumin and were characterized using FTIR, SEM, EDX and AFM. Both the loaded and unloaded nanocarriers were studied for its in-vitro cytotoxic effect against the MCF7 human breast cancer cell lines. The nanocarriers were found to deliver the drug efficiently against the cancer cell line used in this study.

Diarylheptanoids as nutraceutical: A review.

Phenolic compounds are naturally occurring compounds present ubiquitously in plants. They have potential health benefits and substantiate evidence for their nutraceutical applications. Diarylheptanoids are part of the broad class of plant phenolics with structurally divergent compounds. They have been used in traditional medicines and homemade remedies to treat various ailments, as organoleptic additives in foods, and also for aesthetic purposes. With their potential therapeutic and organoleptic characteristics, diarylhepatanoids can be rightly termed as nutraceuticals. This review summarizes the wide range of pharmacological activities of diarylhepatanoids and nutraceutical formulations, with relevance to human health.

Aggressive Angiomyxoma of Inguinoscrotal Region Mimicking Inguinal Hernia: a Case Report.

Aggressive angiomyxoma (AAM) is a rare mesenchymal tumour of pelvis and perineum, almost exclusively occurring in females. We are reporting a case of a 53-year-old gentleman who presented with a long standing inguinoscrotal swelling misdiagnosed as inguinal hernia, for which he underwent incomplete excision at local hospital and then was referred to our centre for completion surgery.

The ratio of pericardial to subcutaneous adipose tissues is associated with insulin resistance.

OBJECTIVE: To examine the association between pericardial adipose tissue (PAT) and the ratio of PAT to subcutaneous adipose tissue (SAT) with insulin resistance in adults with and without type 1 diabetes (T1D). METHODS: Data for this report came from a substudy of the Coronary Artery Calcification in Type 1 Diabetes cohort (n = 83; 38 with T1D, 45 without T1D). Insulin resistance was measured by hyperinsulinemic-euglycemic clamp. Abdominal computed tomography (CT) was used to measure visceral adipose tissue (VAT) and SAT. PAT was measured from CT scans of the heart. RESULTS: PAT and the ratio of PAT to SAT was higher in males compared to females. After adjustment for demographics, diabetes, blood pressure and lipid factors, BMI, VAT, and log PAT/SAT ratio, log PAT was positively associated with the glucose infusion rate (GIR) in females only (ß = 3.36 ± 1.96, P = 0.097, P for sex interaction = 0.055). Conversely, the log PAT/SAT ratio was significantly associated with decreased GIR in both males and females (ß = -2.08 ± 1.03, P = 0.047, P for sex interaction = 0.768). CONCLUSIONS: A significant association between the PAT/SAT ratio and insulin resistance was found, independent of BMI, VAT, and PAT. These results highlight the importance of considering fat distribution independent of volume.

Comparison of the efficacy and safety of sublingual misoprostol with that of vaginal misoprostol for labour induction at term.

OBJECTIVE: To compare the efficacy and safety of 50 mcg of sublingual misoprostol with 25 mcg of vaginal misoprostol for induction of labour at term. METHOD: Non blinded randomized prospective control study. 200 women with singleton term pregnancy, admitted for induction of labour, were randomized to receive either 25 mcg of vaginal misoprostol or 50 mcg of sublingual misoprostol. Outcome measures compared were the number of vaginal deliveries, induction-delivery interval, caesarean section for foetal distress, oxytocin for acceleration, number of doses required, side effects and neonatal outcome. RESULT: Mean dose was smaller and induction to delivery interval was significantly shorter in the sublingual group (13.1 ± 4.1 h) compared with the vaginal group (17.9 ± 5.4 h), p value 0.001. There were no statistically significant differences in the other secondary outcome measures. CONCLUSION: 50 mcg of sublingual misoprostol was more effective than and as safe as 25 mcg vaginal misoprostol for labour induction at term.

CDC Kerala 17: Early detection of developmental delay/disability among children below 3 y in Kerala--a cross sectional survey.

OBJECTIVE: To conduct a community survey to understand the prevalence and type of developmental delay/disability among a representative state wide community sample of children below 3 y. METHODS: A state wide community based cross sectional survey was done with the help of the Integrated Child Development Services (ICDS) network in Kerala after giving one day training program at Child Development Centre (CDC), for one randomly selected anganwadi worker in each of the panchayath/municipal ward, from all districts of Kerala, to equip them to screen all children below 3 y in their anganwadi areas, using simple community screening tools like Trivandrum Developmental Screening Chart (TDSC) 0-3 and Language Evaluation Scale Trivandrum (LEST) 0-3. Those children with one or more item delay in TDSC or LEST were called to the developmental evaluation camps held at ICDS block level and trained pediatrician/medical officer re-evaluated the children with developmental delay. RESULTS: A total of 32,664 children below 3 y were screened across the state and overall 2.5% prevalence of developmental delay was observed using TDSC and 2.8% using LEST 0-3 y and 3.4% using TDSC and/or LEST positive. Out of the total 1,110 children clinically evaluated by a trained pediatrician, 69.3% children had developmental delay, 14.3% speech delay, 5.7% global delay, 5.3% gross motor delay and 3.6% suspected of hearing impairment. CONCLUSIONS: The study results showing 3.4% prevalence of developmental delay using TDSC and/or LEST by trained anganwadi workers or ASHA workers could be replicated in other states in India, under Rashtria Bal Swasthya Kariyakram.

An evaluation of mobile health application tools.

BACKGROUND: The rapid growth in the number of mobile health applications could have profound significance in the prevention of disease or in the treatment of patients with chronic disease such as diabetes. OBJECTIVE: The objective of this study was to describe the characteristics of the most common mobile health care applications available in the Apple iTunes marketplace. METHODS: We undertook a descriptive analysis of a sample of applications in the "health and wellness" category of the Apple iTunes Store. We characterized each application in terms of its health factor and primary method of user engagement. The main outcome measures of the analysis were price, health factors, and methods of user engagement. RESULTS: Among the 400 applications that met the inclusion criteria, the mean price of the most frequently downloaded paid applications was US $2.24 (SD $1.30), and the mean price of the most currently available paid applications was US $2.27 (SD $1.60). Fitness/training applications were the most popular (43.5%, 174/400). The next two most common categories were health resource (15.0%, 60/400) and diet/caloric intake (14.3%, 57/400). Applications in the health resource category constituted 5.5% (22/400) of the applications reviewed. Self-monitoring was the most common primary user engagement method (74.8%, 299/400). A total of 20.8% (83/400) of the applications used two or more user engagement approaches, with self-monitoring and progress tracking being the most frequent. CONCLUSIONS: Most of the popular mobile health applications focus on fitness and self-monitoring. The approaches to user engagement utilized by these applications are limited and present an opportunity to improve the effectiveness of the technology.

Factors that predict 1-month mortality in patients with pregnancy-specific liver disease.

BACKGROUND & AIMS: Pregnancy-specific liver diseases such as acute fatty liver of pregnancy; hemolysis, elevated liver enzymes and low platelet syndrome; and preeclampsia-associated liver disease are associated with considerable morbidity and mortality. We investigated the ability of the model for end-stage liver disease (MELD) to predict 1-month mortality among patients with pregnancy-specific liver diseases. We also developed and tested a model to predict mortality based on features of pregnancy-specific liver diseases. METHODS: We performed a retrospective study, analyzing hospital admission, clinical, hematologic, and biochemical data collected from 130 patients with pregnancy-specific liver diseases admitted to the St. John's Medical College Hospital (Bangalore, India) from January 2000 through April 2011. Patients were followed up until 3 months after delivery or death. Logistic regression models were fitted using the MELD score and other variables identified as clinically or statistically significant. The predictive accuracy and calibration of the models were assessed by receiver operating characteristic curves and the Hosmer-Lemeshow goodness-of-fit test. RESULTS: Thirty-two patients (24.6%) died. Mortalities from pregnancy-specific liver diseases within 1 month of admission among patients with MELD scores of 20 to 29, 30 to 39, or 40 or greater were 24.2%, 45.45%, and 90.9%, respectively. Univariate analysis identified encephalopathy, ascites, serum total protein, bilirubin, platelet count, alkaline phosphatase, serum creatinine, and international normalized ratio (INR) as significant variables. Multivariate analysis identified total bilirubin (P < .001) and INR (P < .003) as significant predictors of mortality. MELD score and a model based on only 2 variables (bilirubin level and INR) accurately predicted mortality (C statistics, 0.83 and 0.86, respectively) and were well calibrated (Hosmer-Lemeshow χ(2) = 9.7 [P = .28] and 1.9 [P = .98], respectively). CONCLUSIONS: A new logistic model based on only 2 variables (INR and total bilirubin) was comparable with the MELD model in predicting mortality among women with pregnancy-specific liver diseases.

A caged, destabilized, free radical intermediate in the q-cycle.

The Rieske/cytochrome b complexes, also known as cytochrome bc complexes, catalyze a unique oxidant-induced reduction reaction at their quinol oxidase (Qo ) sites, in which substrate hydroquinone reduces two distinct electron transfer chains, one through a series of high-potential electron carriers, the second through low-potential cytochrome b. This reaction is a critical step in energy storage by the Q-cycle. The semiquinone intermediate in this reaction can reduce O2 to produce deleterious superoxide. It is yet unknown how the enzyme controls this reaction, though numerous models have been proposed. In previous work, we trapped a Q-cycle semiquinone anion intermediate, termed SQo , in bacterial cytochrome bc1 by rapid freeze-quenching. In this work, we apply pulsed-EPR techniques to determine the location and properties of SQo in the mitochondrial complex. In contrast to semiquinone intermediates in other enzymes, SQo is not thermodynamically stabilized, and can even be destabilized with respect to solution. It is trapped in Qo at a site that is distinct from previously described inhibitor-binding sites, yet sufficiently close to cytochrome bL to allow rapid electron transfer. The binding site and EPR analyses show that SQo is not stabilized by hydrogen bonds to proteins. The formation of SQo involves "stripping" of both substrate -OH protons during the initial oxidation step, as well as conformational changes of the semiquinone and Qo proteins. The resulting charged radical is kinetically trapped, rather than thermodynamically stabilized (as in most enzymatic semiquinone species), conserving redox energy to drive electron transfer to cytochrome bL while minimizing certain Q-cycle bypass reactions, including oxidation of prereduced cytochrome b and reduction of O2 .