Predictors of near-term fracture in osteoporotic women aged ≥65 years, based on data from the study of osteoporotic fractures.

Using data from the Study of Osteoporotic Fractures (SOF), several clinical characteristics predictive of near-term (1-year) risk of hip and non-vertebral fracture among elderly osteoporotic women were identified, and a subset of those for hip fracture was incorporated into a risk assessment tool. Additional research is needed to validate study findings. INTRODUCTION: While several risk factors are known to contribute to long-term fracture risk in women with osteoporosis, factors predicting fracture risk over a shorter time horizon, such as over a 1-year period, are less well-established. METHODS: We utilized a repeated-observations design and data from the Study of Osteoporotic Fractures to identify factors contributing to near-term risk of hip fracture and any non-vertebral fracture, respectively, among osteoporotic women aged ≥65 years. Potential predictors of hip fracture and any non-vertebral fracture over the 1-year period subsequent to each qualifying SOF exam were examined using multivariable frailty models. Because the discriminative ability of the hip fracture model was acceptable, a corresponding risk-prediction tool was also developed. RESULTS: Study population included 2499 women with osteoporosis, who contributed 6811 observations. Incidence of fracture in the 1-year period subsequent to each exam was 2.2% for hip fracture and 6.6% for any non-vertebral fracture. Independent predictors of hip fracture included low total hip T-score, prior fracture, and risk factors for falls (multivariable model c-statistic = 0.71 (95% CI 0.67-0.76)). Independent predictors of any non-vertebral fracture included age, total hip T-score, prior falls, prior fracture, walking speed, Parkinson's disease or stroke, and smoking (multivariable model c-statistic = 0.62 (0.59-0.65)). CONCLUSIONS: Several clinical characteristics predictive of hip and non-vertebral fracture within a 1-year follow-up period among elderly women with osteoporosis were identified, and a subset of those for hip fracture was incorporated into a risk assessment tool. Assessment of these risk factors may help guide osteoporosis treatment choices by identifying patients in whom there is urgency to treat. Additional research is needed to validate the findings of this study and the accuracy of the risk assessment tool.

[Generalized anxiety disorder in primary care. Patterns of healthcare utilization in Germany]. / Generalisierte Angststörung in der primärärztlichen Versorgung. Eine Analyse administrativ-epidemiologischer Daten zu Inanspruchnahme und Versorgungsmerkmalen.

BACKGROUND: Generalized Anxiety Disorder (GAD) has been described in community studies as a frequent and costly high utilizer group in the primary care sector. Administrative data supporting this observation are lacking so far. METHODS: This paper reports utilization and prescription data of a nationally representative sample of over 900 primary care physicians, over 75 million prescriptions and 12-month utilization and prescription patterns of n = 3,340 GAD patients.These are compared to a matched control group without GAD, and without any anxiety or depressive disorder (n = 3,340). RESULTS: GAD patients in comparison to the matched controls revealed: (1) 2-fold increased primary care, (2) almost 3-fold specialist referrals, (3) almost 2-fold increased overall prescription rates, and (4) 3.5-fold increased sick certificates. However, only 58.3% of GAD patients were treated with any psychotropic medication. DISCUSSION: The data of this administrative-epidemiological cohort study support strongly the view that GAD ranks among the most costly high utilizer patient group in primary care in Germany. However, they are rarely treated according to evidence-based guidelines. The paper discusses these findings by suggesting that comorbid conditions might be a barrier for primary care physicians to initiate existing, more appropriate state of the art treatments.

Treatment of new-onset ulcerative colitis and ulcerative proctitis: a retrospective study.

BACKGROUND: Although guidelines recommend use of oral 5-aminosalicylates (5-ASAs) as first-line therapy in patients with mild to moderate ulcerative colitis (UC) and ulcerative proctitis (UP) and steroids with or without 5-ASAs in those more severely ill, little is known about how UC and UP are actually treated. AIM: To document treatment of new-onset UC and UP in routine clinical practice. METHODS: Using a large US health insurance database, we identified all persons with new-onset UC or UP between 1 January 2005 and 31 December 2007, based on: (i) initial receipt of an oral 5-ASA, mesalazine (mesalamine) suppository, 5-ASA enema, steroid, antimetabolite, budesonide or TNF inhibitor; (ii) sigmoidoscopy/colonoscopy in prior 30 days resulting in a new diagnosis of UC or UP and (iii) no prior encounters for Crohn's disease. We examined patterns of pharmacotherapy over 1 year. RESULTS: We identified 1516 UC patients and 636 UP patients who met study entry criteria. In UC, initial therapies most frequently used were oral 5-ASAs (53% of patients), oral 5-ASAs and systemic steroids (12%), systemic steroids (8%) and mesalazine suppositories (6%); in UP, mesalazine suppositories (42%) and oral 5-ASAs (19%) were most often used, followed by combination therapy (14%), mesalazine enema (11%) and rectal steroids (10%). Few patients received maintenance therapy, and there was limited use of antimetabolites and biological agents. CONCLUSIONS: Oral 5-ASAs and systemic steroids are the mainstay of treatment in patients with new-onset ulcerative colitis; in those with new-onset ulcerative proctitis, it is mesalazine suppositories. Care of these patients appears consistent with treatment guidelines.

Cost-effectiveness of abatacept in patients with moderately to severely active rheumatoid arthritis and inadequate response to methotrexate.

OBJECTIVE: To assess cost-effectiveness of abatacept in patients with moderately to severely active RA and inadequate response to MTX. METHODS: We developed a simulation model to depict progression of disability [in terms of the HAQ Disability Index (HAQ-DI)] in women aged 55-64 yrs with moderately to severely active RA and inadequate response to MTX. At model entry, patients were assumed to receive either only MTX or MTX plus abatacept. Patients were then tracked from model entry until death. Future health-state utilities and medical-care costs (except study therapy) were estimated based on predicted values of the HAQ-DI. The model was estimated using data from a Phase III clinical trial of abatacept plus various secondary sources. Cost-effectiveness was expressed in terms of incremental cost (2006 US$) per quality-adjusted life-year (QALY) gained over alternatively 10 yrs and a lifetime. Costs and health effects were both discounted at 3% annually. RESULTS: Over 10 yrs, abatacept would yield 1.2 additional QALYs (undiscounted) per patient (4.6 vs 3.4 for MTX) at an incremental (discounted) cost of $51,426 ($103,601 vs $52,175, respectively); over a lifetime, corresponding figures were 2.0 QALYS (6.8 vs 4.8) and $67,757 ($147,853 vs $80,096). Cost-effectiveness was [mean (95% CI)] $47,910 ($44,641, $52,136) per QALY gained over 10 yrs and $43,041 ($39,070, $46,725) per QALY gained over a lifetime. Findings were robust in sensitivity analyses. CONCLUSION: Abatacept is cost-effective by current standards of medical practice in patients with moderately to severely active RA and inadequate response to MTX.

Risk of chronic kidney disease in hypertensive patients with other metabolic conditions.

Using a retrospective cohort design and electronic medical records, we examined chronic kidney disease (CKD) risk over a 6-year period among hypertensive patients in relation to the presence of diabetes, hyperlipidaemia and/or high body mass index. After adjusting for age, sex, smoking status and baseline glomerular filtration rate (GFR), hypertensive patients without other metabolic risk factors had a relative risk of CKD (versus normotensive patients) of 2.0 (95% CI 1.8-2.2); hypertensive patients with other metabolic conditions had adjusted relative risks ranging from 2.4 to 2.6 for those without comorbid diabetes, and from 3.3 to 5.5 for those with comorbid diabetes. Our study thus confirms prior research demonstrating elevated CKD risk in hypertensive patients, and suggests that this risk varies substantially in relation to other metabolic conditions, especially diabetes.

Cost of neutropenic complications of chemotherapy.

BACKGROUND: Cost of neutropenic complications of myelosuppressive chemotherapy has been reported to be substantial. Prior research, however, has focused on initial hospitalization only and has failed to account for follow-on care. PATIENTS AND METHODS: Using a US health-care claims database, all adult cancer patients who received a course of chemotherapy were identified. For each such patient, each unique cycle of chemotherapy within the course and each occurrence of neutropenic complications within these cycles were characterized. Patients developing neutropenic complications in a given cycle (neutropenia patients), starting with the first, were matched (1:1) to those who did not develop neutropenic complications in that cycle (comparison patients), and health-care costs (i.e. expenditures) were tallied for each matched pair. RESULTS: Neutropenia patients (n = 373) and comparison patients were similar in terms of baseline characteristics. Costs of neutropenia-related care were $12,397 (95% confidence interval $10,274-$14,754) higher for neutropenia versus comparison patients [$14,407 ($12,357-$16,743) versus $2010 ($1490-$2553)]. Among neutropenia patients, mean cost of initial hospitalization for neutropenic complications was $7813 ($6537-$9379); cost of all subsequent neutropenia-related care averaged $6594 ($5217-$8272). CONCLUSIONS: Neutropenic complications of myelosuppressive chemotherapy are costly. Prior research focusing on initial hospitalization only may have underestimated the cost of these complications by as much as 40%.

Characteristics and healthcare costs of patients with fibromyalgia syndrome.

PURPOSE: To examine the characteristics and healthcare costs of fibromyalgia syndrome (FMS) patients in clinical practice. MATERIALS AND METHODS: Using a US health-insurance database, we identified all patients, aged > or = 18 years, with any healthcare encounters for FMS (ICD-9-CM diagnosis code 729.1) in each year of the 3-year period, 1 July 2002 to 30 June 2005. A comparison group was then constituted, consisting of randomly selected patients without any healthcare encounters for FMS during this 3-year period. Comparison group patients were matched to FMS patients based on age and sex. Characteristics and healthcare costs of FMS patients and comparison group patients were then examined over the 1-year period, 1 July 2004 to 30 June 2005 (the most recent year for which data were available at the time of the study). RESULTS: The study sample consisted of 33,176 FMS patients and an identical number in the comparison group. Mean age was 46 years, and 75% were women. FMS patients were more likely to have various comorbidities, including painful neuropathies (23% vs. 3% for comparison group), anxiety (5% vs. 1%), and depression (12% vs. 3%) (all p < 0.001); they also were more likely to have used pain-related pharmacotherapy (65% vs. 34% for comparison group; p < 0.001). Mean (SD) total healthcare costs over 12 months were about three times higher among FMS patients [$9573 ($20,135) vs. $3291 ($13,643); p < 0.001]; median costs were fivefold higher ($4247 vs. $822; p < 0.001). CONCLUSIONS: Patients with FMS have comparatively high levels of comorbidities and high levels of healthcare utilization and cost.

Use of antiepileptics and tricyclic antidepressants in cancer patients with neuropathic pain.

Using a large US health insurance claims database, we identified all persons aged > or =18 years with > or =2 medical encounters with diagnoses of cancer and > or =2 medical encounters with diagnoses of painful neuropathies in calendar year (CY) 2000; persons with seizure disorders or depression were excluded. We then examined the use of antiepileptics (AEDs), tricyclic antidepressants (TCAs) and other pain-related pharmacotherapy among these selected persons, as proxied by pharmacy dispenses. A total of 956 persons were identified who met all entry criteria; 17% received AEDs in CY2000 and 14% received TCAs. Gabapentin was the most widely used AED (92% of all AED patients); amitriptyline was the most widely used TCA (79% of all TCA patients). Patients who received AEDs and/or TCAs were similar in age, gender and the presence of metastases to those who had not received these medications; they were more likely to have received other pain-related therapies, however, including short-acting opioids (73% vs. 53%; P < 0.01) and long-acting opioids (23% vs. 8%; P < 0.01). Use of AEDs and TCAs appears to be relatively low among cancer patients with painful neuropathies. Further research is needed to better understand reasons for this finding, as well as its potential implications for pain management in this patient population.

Venous thromboembolism following major orthopedic surgery: review of epidemiology and economics.

The epidemiology and economics of venous thromboembolism (VTE) associated with hip and knee arthroplasty and surgical repair of hip fracture are reviewed. In the 1960s and 1970s, prior to the widespread use of prophylaxis, the risk of VTE following major orthopedic surgery was substantial. The risk of fatal pulmonary embolism (PE) following hip fracture repair may have been as high as 7.5%. With improvements in surgical and anesthetic techniques and the use of anticoagulant prophylaxis, these risks have decreased significantly for most patients. Current risks after hip and knee arthroplasty appear to be about 2.5% for deep vein thrombosis, 1% for nonfatal PE, and a few tenths of 1% for fatal PE over a three-month period following surgery. Because of the traumatic nature of the injury, delays in getting to surgery, and their more advanced age and poorer overall health, hip fracture patients appear to have a greater risk of postoperative VTE, but data are lacking for a reliable estimate of current risk. The cost of VTE after major orthopedic surgery includes initial therapy (the chief component), follow-up care, and the expected costs of major hemorrhage (due to anticoagulation), recurrent VTE, and postthrombotic syndrome. The total cost per patient of such care is approximately $11,600. The risk of VTE after surgery to replace hip and knee joints and repair hip fracture is far lower today than in the 1960s and 1970s, but the cost of treating VTE remains high: an estimated $11,600 per patient, including hospitalization costs.

The physics of molecular motors.

Molecular motors convert chemical energy into mechanical force and movement. Operating at energies just above those of the thermal bath, these motors experience large fluctuations, and their physical description must be necessarily stochastic. Here, motor operation is described as a biased diffusion on a potential energy surface defined by the interactions of the motor with its track and its fuel. These ideas are illustrated with a model of the rotary movement of the F(o) motor.

Oral mucositis and the clinical and economic outcomes of hematopoietic stem-cell transplantation.

PURPOSE: To explore the relationship between oral mucositis and selected clinical and economic outcomes in blood and marrow transplant patients. PATIENTS AND METHODS: Subjects consisted of 92 transplant patients from eight centers who participated in a multinational pilot study of a new oral mucositis scoring system (Oral Mucositis Assessment Scale [OMAS]). In the pilot study, patients were evaluated for erythema and ulceration/pseudomembrane formation beginning on the first day of conditioning and continuing for 28 days. We examined the relationship between patients' peak OMAS scores and days with fever (body temperature > 38.0 degrees C), the occurrence of significant infection, days of total parenteral nutrition (TPN), and days of injectable narcotic therapy (all over 28 days), days in hospital (over 60 days), total hospital charges for the index admission, and vital status at 100 days. RESULTS: Patients' peak OMAS scores spanned the full range of possible values (0 to 5) and were significantly (P <.05) correlated with all of the outcomes of interest except days with fever (P =.21). In analyses controlling for type of graft (autologous v allogeneic) and study center, a 1-point increase in peak OMAS score was associated with (1) 1.0 additional day with fever (P <.01), (2) a 2.1-fold increase in risk of significant infection (P <.01), (3) 2.7 additional days of TPN (P <.0001), (4) 2.6 additional days of injectable narcotic therapy (P <.0001), (5) 2.6 additional days in hospital (P <.01), (6) $25,405 in additional hospital charges (P <.0001), and (7) a 3.9-fold increase in 100-day mortality risk (P <.01). Mean hospital charges were $42,749 higher among patients with evidence of ulceration compared with those without (P =.06). CONCLUSION: Oral mucositis is associated with significantly worse clinical and economic outcomes in blood and marrow transplantation.

Body mass index and future healthcare costs: a retrospective cohort study.

OBJECTIVE: To assess the relationship between body mass index (BMI) and future healthcare costs. RESEARCH METHODS AND PROCEDURES: We undertook a retrospective cohort study of the relationship between obesity and future healthcare costs at Kaiser Permanente Northwest Division, a large health maintenance organization in Portland, Oregon. Study subjects (n = 1286) consisted of persons who responded to a 1990 health survey that was mailed to a random sample of adult Kaiser Permanente Northwest Division members who were 35 to 64 years of age; had a BMI > or = 20 kg/m(2) (based on self-reported height and weight); did not smoke cigarettes; and did not have a history of coronary heart disease, stroke, human immunodeficiency virus, or cancer. Subjects were stratified according to their BMI in 1990 (20 to 24.9, 25 to 29.9, and > or = 30 kg/m(2); n = 545, 474, and 367, respectively). We then tallied their costs (in 1998 US dollars) for all inpatient care, outpatient services, and prescription drugs over a 9-year period (1990 through 1998). RESULTS: For persons with BMIs of 20 to 24.9 kg/m(2), mean (+/-SE) annual costs of prescription drugs, outpatient services, inpatient care, and all medical care averaged $261 (+/-18), $848 (+/-59), $532 (+/-85), and $1631 (+/-120), respectively, over the study period. Cost ratios (95% confidence intervals) for persons with BMIs of 25 to 29.9 kg/m(2) and > or = 30 kg/m(2), respectively, were 1.37 (1.12 to 1.66) and 2.05 (1.62 to 2.55) for prescription drugs, 0.96 (0.83 to 1.13) and 1.14 (0.97 to 1.37) for outpatient services, 1.20 (0.81 to 1.86) and 1.38 (0.91 to 2.14) for inpatient care, and 1.10 (0.91 to 1.35) and 1.36 (1.11 to 1.68) for all medical care. DISCUSSION: Future healthcare costs are higher for persons who are overweight, especially those with BMIs > or = 30 kg/m(2).

A randomized trial of controlled-release oxycodone during inpatient rehabilitation following unilateral total knee arthroplasty.

BACKGROUND: Reliance on "as-needed" analgesia following total knee arthroplasty may lead to inadequate control of pain and delayed recovery of function. Preemptive use of controlled-release opioids may improve pain control, accelerate recovery, and reduce the need for inpatient rehabilitative services. This study was designed to determine whether controlled-release opioids enhance post-arthroplasty pain control and facilitate functional recovery during rehabilitation. METHODS: Fifty-nine patients admitted for inpatient rehabilitation following unilateral total knee arthroplasty were randomized to receive OxyContin (controlled-release oxycodone) (twenty-nine patients) or a placebo (thirty patients) every twelve hours. Both groups could receive on-request, immediate-release oxycodone (5 mg every four hours). The dose of study medication was increased on the basis of the frequency of requests for immediate-release oxycodone. Measures of interest included pain ratings as determined with a visual-analog scale, changes in the range of motion of the knee and quadriceps strength, and improvements in selected Functional Independence Measure scores during the first eight physical therapy sessions. The duration of the hospital stay for rehabilitation also was compared between the two groups. RESULTS: Baseline demographic, clinical, and functional characteristics were similar between the OxyContin and placebo groups. Compared with the placebo group, the patients who received OxyContin reported significantly less pain as well as significantly greater range of motion of the knee (passive motion, p = 0.036; active motion, p< 0.001) and quadriceps strength (p = 0.001) by the eighth physical therapy session. The patients who received OxyContin also were discharged from the rehabilitation hospital at an average of 2.3 days earlier than the patients in the placebo group (p = 0.013). CONCLUSIONS: Preemptive use of controlled-release oxycodone during rehabilitation following total knee arthroplasty leads to improved pain control, more rapid functional recovery, and a reduced need for inpatient rehabilitative services.

Regulation of organelle acidity.

Intracellular organelles have characteristic pH ranges that are set and maintained by a balance between ion pumps, leaks, and internal ionic equilibria. Previously, a thermodynamic study by Rybak et al. (Rybak, S., F. Lanni, and R. Murphy. 1997. Biophys. J. 73:674-687) identified the key elements involved in pH regulation; however, recent experiments show that cellular compartments are not in thermodynamic equilibrium. We present here a nonequilibrium model of lumenal acidification based on the interplay of ion pumps and channels, the physical properties of the lumenal matrix, and the organelle geometry. The model successfully predicts experimentally measured steady-state and transient pH values and membrane potentials. We conclude that morphological differences among organelles are insufficient to explain the wide range of pHs present in the cell. Using sensitivity analysis, we quantified the influence of pH regulatory elements on the dynamics of acidification. We found that V-ATPase proton pump and proton leak densities are the two parameters that most strongly influence resting pH. Additionally, we modeled the pH response of the Golgi complex to varying external solutions, and our findings suggest that the membrane is permeable to more than one dominant counter ion. From this data, we determined a Golgi complex proton permeability of 8.1 x 10(-6) cm/s. Furthermore, we analyzed the early-to-late transition in the endosomal pathway where Na,K-ATPases have been shown to limit acidification by an entire pH unit. Our model supports the role of the Na,K-ATPase in regulating endosomal pH by affecting the membrane potential. However, experimental data can only be reproduced by (1) positing the existence of a hypothetical voltage-gated chloride channel or (2) that newly formed vesicles have especially high potassium concentrations and small chloride conductance.

The clinical and economic burden of obesity in a managed care setting.

OBJECTIVE: To estimate the clinical and economic burden of obesity in a managed care setting. STUDY DESIGN: Prevalence-based cost-of-illness evaluation using modeling techniques and data from secondary sources. PATIENTS AND METHODS: The health and economic burden of obesity was estimated for a hypothetical health plan with 1 million members between the ages of 35 and 84 years, based on projections of the numbers of cases of 8 diseases for which obesity is an established risk factor (coronary heart disease, hypertension, hypercholesterolemia, gallbladder disease, stroke, type 2 diabetes, osteoarthritis of the knee, and endometrial cancer), obesity-attributable "etiologic fractions," and estimates of associated medical care costs. Our analysis was based on data from a variety of secondary sources, including a large managed care plan in the Pacific Northwest region of the United States. RESULTS: In a population of 1 million persons aged 35 to 84 years, it was estimated that obesity would account for approximately 132,900 cases of hypertension (45% of all cases), 58,500 cases of type 2 diabetes (85%), 51,500 cases of hypercholesterolemia (18%), and 16,500 cases of coronary heart disease (35%). Healthcare costs attributable to obesity were estimated to total $345.9 million annually (or 41% of the total for the 8 diseases of interest). CONCLUSION: The clinical and economic burden of obesity in a managed care setting is substantial.

Use of rhDNase therapy and costs of respiratory-related care in patients with cystic fibrosis.

OBJECTIVE: To assess the relationship between level of use of recombinant deoxyribonuclease I (rhDNase) therapy and costs of respiratory-related care in patients with cystic fibrosis. DESIGN: Retrospective, cohort study using healthcare claims data from a large New England health insurer. PATIENTS: All cystic fibrosis patients five years of age and older who began therapy with rhDNase in 1994 (the year it was first marketed in the US). Healthcare claims were compiled for six months prior to first receipt of rhDNase (pretreatment) and for 30 months subsequently (follow-up). Patients were stratified according to their level of rhDNase use during follow-up, based on whether it was above or below the median number of therapy days for the sample. MAIN OUTCOME MEASURES: Costs of rhDNase, all antibiotics, and all respiratory-related outpatient (physician, home health, hospital outpatient) and inpatient care were included. All costs were expressed on an annualized basis. RESULTS: Twenty-four patients with cystic fibrosis who began treatment with rhDNase in 1994 met all entry criteria; the median number of therapy days over a 30-month period was 355. Among patients with low (i.e., below the median) rhDNase use (n = 12), mean +/- SD annualized costs of respiratory-related care increased by almost $17,000 between pretreatment and follow-up, from $29,251 +/- $37,919 to $46,109 +/- $40,944. Among high-use patients (n = 12), costs decreased by approximately $2500, from $37,178 +/- $48,476 to $34,592 +/- $22,591. The change in both groups was accounted for primarily by a change in the number of respiratory-related hospitalizations. CONCLUSIONS: Prolonged use of rhDNase may reduce costs of respiratory-related care in patients with cystic fibrosis; further study is required, however, to confirm these findings.

How Fo-ATPase generates rotary torque.

The F-ATPases synthesize ATP using a transmembrane ionmotive force (IMF) established by the electron transport chain. This transduction involves first converting the IMF to a rotary torque in the transmembrane Fo portion. This torque is communicated from Fo to the F1 portion where the energy is used to release the newly synthesized ATP from the catalytic sites according to Boyer's binding change mechanism. Here we explain the principle by which an IMF generates this rotary torque in the Fo ion engine.

Reverse engineering a protein: the mechanochemistry of ATP synthase.

ATP synthase comprises two rotary motors in one. The F(1) motor can generate a mechanical torque using the hydrolysis energy of ATP. The F(o) motor generates a rotary torque in the opposite direction, but it employs a transmembrane proton motive force. Each motor can be reversed: The F(o) motor can drive the F(1) motor in reverse to synthesize ATP, and the F(1) motor can drive the F(o) motor in reverse to pump protons. Thus ATP synthase exhibits two of the major energy transduction pathways employed by the cell to convert chemical energy into mechanical force. Here we show how a physical analysis of the F(1) and F(o) motors can provide a unified view of the mechanochemical principles underlying these energy transducers.

The mechanochemistry of V-ATPase proton pumps.

The vacuolar H(+)-ATPases (V-ATPases) are a universal class of proton pumps that are structurally similar to the F-ATPases. Both protein families are characterized by a membrane-bound segment (V(o), F(o)) responsible for the translocation of protons, and a soluble portion, (V(1), F(1)), which supplies the energy for translocation by hydrolyzing ATP. Here we present a mechanochemical model for the functioning of the V(o) ion pump that is consistent with the known structural features and biochemistry. The model reproduces a variety of experimental measurements of performance and provides a unified view of the many mechanisms of intracellular pH regulation.

Why is the mechanical efficiency of F(1)-ATPase so high?

The experimentally measured mechanical efficiency of the F(1)-ATPase under viscous loading is nearly 100%, far higher than any other hydrolysis-driven molecular motor (Yasuda et al., 1998). Here we give a molecular explanation for this remarkable property.