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At least 451 records · Page 25Linked to original sources
PubMed1980

Stable isotope fractionation by Clostridium pasteurianum. 3. Effect of SeO32- on the physiology and associated sulfur isotope fractionation during SO32- and SO42- reductions.

Increased SeO32- concentration reduced H2S evolution from SO32- during whole cell and cell-free extract reductions by Clostridium pasteurianum. H2S production from SO42- was completely inhibited by SeO32- in stationary phase cells. Generation times increased with greater SeO32- concentration, the increase with 1 mM SeO32- being a factor of 2.5 for 1 mM SO32-, and over 3 for 1 mM SO42- reductions. In vitro and in vivo experiments with proposed intermediates of the SO32- reduction pathway show that SeO32- inhibited both the S3O62- to S2O32- and S2O32- to S2- reaction sequences with the latter being more pronounced in growth experiments. Both extracts and whole cells reduced SeO32- to Se0 but Se0 granules were not found in the cell's cytoplasm. The formation of S2O32- by an extracellular chemical mechanism appears not to have occurred in these experiments. Increased SeO32- concentration had the effect of compressing the isotopic release pattern for H2S along the H2S production axis and did not significantly alter the maximum and minimum values of delta 34S. Thus, inhibition by SeO32- limited the conversions of sulfur species without altering the isotopic selectivity of rate-controlling steps in the pathway.

Cell-Free System↗
PubMed2000

Diastolic fractional flow reserve to assess the functional severity of moderate coronary artery stenoses: comparison with fractional flow reserve and coronary flow velocity reserve.

BACKGROUND: Coronary blood flow occurs mainly during the diastolic phase of each cardiac cycle and is mainly dependent on diastolic driving pressure, especially in the left anterior descending coronary artery (LAD). We hypothesized that calculation of the ratio of the diastolic driving pressure of a stenotic LAD to its normal value, namely diastolic FFR (d-FFR), might provide precise insight into the mechanism of FFR for assessment of the functional severity of the stenosis. We compared d-FFR with FFR, coronary flow reserve (CFR), and exercise myocardial thallium scintigraphy in an lesion of intermediate severity. METHODS AND RESULTS: The study population consisted of 46 consecutive patients with a moderate stenosis in the LAD in whom simultaneous measurements of aortic pressure, left ventricular pressure, and coronary pressure distal to the stenosis were obtained. Coronary flow velocity was successfully measured with a Doppler guidewire in 37 of the 46 patients. Values for FFR, d-FFR, and CFR in the noninvasive test-positive group were significantly lower than those in the negative group. With cutoff values of 0.75, 0.76, and 2.0 for FFR, d-FFR, and CFR, sensitivities were 83.3%, 95.8%, and 88.2% and specificities were 100%, 100%, and 95.0%, respectively. CONCLUSIONS: The close similarity of the sensitivity and specificity of FFR and d-FFR, around almost identical cutoff values (0.75 versus 0.76), confirms the physiological validity of FFR as a clinical standard. In clinical practice, FFR remains the index of choice for assessment of the functional severity of moderate coronary artery stenoses.

Blood Flow Velocity↗