The timing of proton migration in membrane-reconstituted cytochrome c oxidase

In mitochondria and aerobic bacteria energy conservation involves electron transfer through a number of membrane-bound protein complexes to O2. The reduction of O2, accompanied by the uptake of substrate protons to form H2O, is catalyzed by cytochrome c oxidase (CcO). This reaction is coupled to proton translocation (pumping) across the membrane such that each electron transfer to the catalytic site is linked to the uptake of two protons from one side and the release of one proton to the other side of the membrane. To address the mechanism of vectorial proton translocation, in this study we have investigated the solvent deuterium isotope effect of proton-transfer rates in CcO oriented in small unilamellar vesicles. Although in H2O the uptake and release reactions occur with the same rates, in D2O the substrate and pumped protons are taken up first (tau(D) congruent with 200 micros, "peroxy" to "ferryl" transition) followed by a significantly slower proton release to the other side of the membrane (tau(D) congruent with 1 ms). Thus, the results define the order and timing of the proton transfers during a pumping cycle. Furthermore, the results indicate that during CcO turnover internal electron transfer to the catalytic site is controlled by the release of the pumped proton, which suggests a mechanism by which CcO orchestrates a tight coupling between electron transfer and proton translocation.     

Glucose homeostasis and safety in patients with acromegaly converted from long-acting octreotide to pegvisomant

CONTEXT: In clinical practice, patients with acromegaly may be switched from therapy with long-acting somatostatin analogs to pegvisomant. The effect of changing therapies on glucose homeostasis and safety has not been reported. OBJECTIVES: The objectives of this study were to monitor changes in IGF-I levels, glycemic control, and safety, particularly liver function and tumor size. DESIGN: This was a multicenter, open-label, 32-wk trial study. SETTING: The study was performed at outpatient clinics. PATIENTS: Fifty-three patients with acromegaly previously treated with octreotide long-acting release (LAR) participated in this study. Intervention: Pegvisomant (10 mg/d) was initiated 4 wk after the last dose of octreotide LAR and was adjusted based on serum IGF-I concentrations at wk 12, 20, and 28. MAIN OUTCOME MEASURES: The main outcome measures were changes in IGF-I, glycosylated hemoglobin A1c (HbA1c), fasting plasma glucose, and safety during the first 12 wk after conversion. RESULTS: At the end of pegvisomant treatment, IGF-I was normalized in 78% of patients. At wk 32, median fasting glucose concentration and HbA1c were reduced (-1.4 mmol/liter and -0.4%, respectively; both P < or = 0.0001) in the study population. Improvements in glycemic control occurred in patients with normal IGF-I concentrations at wk 4 [n = 15; fasting glucose, -1.7 mmol/liter (P < or = 0.0001); HbA1c -0.2% (P = 0.03)]. Decreases in fasting glucose and HbA1c levels were observed in patients with and without diabetes. HbA1c was reduced by more than 1.0% in patients with diabetes. Median pituitary tumor volume did not change, although tumor volume increased in two patients with macroadenomas. CONCLUSIONS: Conversion from octreotide LAR to pegvisomant was safe and well tolerated. Improved glycemic control indicates that pegvisomant should be considered in patients with acromegaly and diabetes.     

Anticoagulation in patients with atrial fibrillation,thrombocytopenia and hematological malignancy

Journal of Thrombosis and Thrombolysis - Managing anticoagulation in hematological malignancy patients with atrial fibrillation and thrombocytopenia is a clinical challenge with limited data. We...     

Time course of hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase activity and messenger ribonucleic acid, biliary lipid secretion, and hepatic cholesterol content in methimazole-treated hypothyroid and hypophysectomized rats after triiodothyronine administration: possible linkage of cholesterol synthesis to biliary secretion

In an effort to define the mechanism by which thyroid hormone increases the synthesis of hepatic cholesterol, we have investigated both in hypophysectomized and methimazole-treated hypothyroid rats the time course of T3 effects on plasma cholesterol concentration, total hepatic cholesterol, the rate of biliary secretion of cholesterol, bile acids, and phospholipids, and the activity and mRNA levels of 3-hydroxy-3-methylglutaryl coenzyme-A (HMG-CoA) reductase, the rate-limiting enzyme in the hepatic synthesis of cholesterol. A single dose of 200 micrograms T3 was estimated to maintain at least 90% nuclear occupancy for the ensuing 54 h of the experiment. In both preparations the relative rise in biliary secretion of cholesterol exceeded that of other biliary constituents and preceded by 12 h an increase in HMG-CoA reductase enzyme activity and its mRNA. The level of total hepatic cholesterol remained constant throughout the experiment. We interpret these findings to suggest that T3-stimulated cholesterol synthesis is mediated by an antecedent T3-induced rise in biliary cholesterol secretion. We postulate that biliary cholesterol secretion is augmented by an intrahepatic shift of cholesterol and depletion of the hepatic sampling center responsible for the feedback regulation of cholesterol synthesis. The level of HMG CoA reductase mRNA appeared to govern enzyme activity in both preparations, but the ratio of mRNA to hepatic enzyme activity was substantially greater in the methimazole-treated compared with the hyphophysectomized animals.