The present results indicate that SEPP1 concentration is the best plasma biomarker studied for assessing optimal expression of all selenoproteins, because its optimization required a larger intake of selenium than did GPX activity. On the basis of the selenium intake needed for SEPP1 optimization with adjustments for body weight and individual variation, ap 75 micro g Se/d as selenomethionine is postulated to allow full expression of selenoproteins in US residents. This trial was registered at clinicaltrials.gov as NCT00428649.
Full expression of selenoprotein P requires a greater selenium intake than does full expression of plasma glutathione peroxidase. This suggests that selenoprotein P is a better indicator of selenium nutritional status than is glutathione peroxidase and that the recommended dietary allowance of selenium, which was set with the use of glutathione peroxidase as the index of selenium status, should be revised. Selenium as selenomethionine had nearly twice the bioavailability of selenium as selenite.
Selenoprotein P, a selenium-rich plasma protein, is an index of selenium status in rats. Antibodies against human selenoprotein P were raised to study the protein and to develop a radioimmunoassay for it. A single collection of plasma from a healthy person in the United States contained 1.84 mumol selenium/L and was defined as containing 1 Unit (U) selenoprotein P/L. Removal of selenoprotein P from the reference plasma by an antibody column indicated that 0.81 mumol selenium/L, or 44% of the plasma selenium, was present as selenoprotein P. Work by others had determined that glutathione peroxidase accounted for 12% of plasma selenium. Stored plasma samples from selenium-deficient (Dechang County) and selenium-supplemented (Mianning County) populations in China were assayed for selenoprotein P. Boys aged 8-12 y had selenoprotein P concentrations of 0.10 +/- 0.04 U/L (n = 22) in Dechang and 0.39 +/- 0.17 U/L (n = 17) in Mianning. Supplementation with 100 micrograms selenium as selenate per day for 14 d raised those levels to 0.51 +/- 0.13 U/L in Dechang and to 0.76 +/- 0.27 U/L in Mianning. Similar results were obtained in men, and plasma selenium concentrations correlated with selenoprotein P concentrations. A study comparing indices of selenium status was conducted in the two counties. Selenoprotein P concentration in Dechang subjects (n = 79) was 36% of that in Mianning subjects (n = 117). For plasma glutathione peroxidase activity the value was 54%; for plasma selenium, 47%; and for whole blood selenium, 64%. We conclude that selenoprotein P is the major selenoprotein in human plasma and that its concentration is an index of selenium nutritional status that appears to be as sensitive as other indices in common use.
A new maximum power point tracking technique for permanent magnet synchronous generator based wind energy conversion systems is proposed. The technique searches for the system optimum relationship for maximum power point tracking and then controls the system based on this relationship. The validity of the technique is theoretically analyzed, and the design procedure is presented. The primary merit of the proposed technique is that it does not require an anemometer or preknowledge of a system, but has an accurate and fast response to wind speed fluctuations. Moreover, it has the ability of online updating of time-dependant turbine or generator parameter shift. The validity and performance of the proposed technique are confirmed by MATLAB/Simulink simulations and experimentations. Index Terms-Maximum power point tracking (MPPT), permanent magnet synchronous generator (PMSG), power coefficient, wind energy.
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